What Is Salmonella?

Salmonella is a genus of rod-shaped Gram-negative enterobacteria that causes typhoid fever, paratyphoid and foodborne illness. Salmonella does not ferment lactose. It is motile in nature and produces hydrogen sulfide.

Disease-causing salmonellae have recently been re-classified into a single species, Salmonella enterica, which has numerous strains or serovars. Salmonella typhi is a well known serovar that causes typhoid fever. Other salmonellae are frequent causes of foodborne illness, and can especially be caught from poultry. In the mid to late 20th century, Salmonella enterica serovar Enteritidis was a common contaminant of eggs. This is much less common now with the advent of hygiene measures in egg production and the vaccination of laying hens to prevent samonella colonisation. Many different salmonella serovars also cause severe diseases in animals other than human beings.

Salmonellosis is an infection with Salmonella bacteria. Most persons infected with Salmonella develop diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts 4 to 7 days, and most persons recover without treatment. However, in some persons the diarrhea may be so severe that the patient needs to be hospitalized. In these patients, the Salmonella infection may spread from the intestines to the blood stream, and then to other body sites and can cause death unless the person is treated promptly with antibiotics. The elderly, infants, and those with impaired immune systems are more likely to have a severe illness.

Foodborne illness or food poisoning is caused by consuming food contaminated with pathogenic bacteria, toxins, viruses, prions or parasites. Such contamination usually arises from improper handling, preparation or storage of food. Foodborne illness can also be caused by adding pesticides or medicines to food, or consuming or by accidentally consuming naturally poisonous substances like poisonous mushrooms or reef fish. Contact between food and pests, especially flies, rodents and cockroaches, is a further cause of contamination of food.

Some common diseases are occasionally foodborne mainly through the water vector, even though they are usually transmitted by other routes. These include infections caused by Shigella, Hepatitis A, and the parasites Giardia lamblia and Cryptosporidium parvum.

Salmonella enterica is a species of Salmonella bacterium. S. enterica has a number of varieties or serovars. Serovar Typhi (sometimes elevated to species status as S. typhi) is the disease agent in typhoid. Other serovars such as Typhimurium (also known as S. typhimurium) can lead to a form of human gastroenteritis sometimes referred to as salmonellosis.

Most cases of salmonellosis are caused by food infected with S. enterica, which often infects cattle, though also other animals such as domestic cats. However, investigations of vacuum cleaner bags have shown that households can act as a reservoir of the bacterium; this is more likely if the household has contact with an infection source, for example through members working with cattle or in a veterinary clinic.

The genome sequences of serovars Typhi and Typhimurium LT2 have been established.

S. typhi S. typhi is a serovar of Salmonella. It causes the disease typhoid fever. The organism can be transmitted by the fecal-oral route -- it is excreted by humans in feces and may be transmitted by contaminated water, food, or by person to person contact (with inadequate attention to personal hygiene).

Salmonella species are Gram-negative, flagellated facultatively anaerobic bacilli characterized by O, H, and Vi antigens. There are over 1800 known serovars which current classification considers to be separate species.

Pathogenesis Pathogenic salmonellae ingested in food survive passage through the gastric acid barrier and invade the mucosa of the small and large intestine and produce toxins. Invasion of epithelial cells stimulates the release of proinflammatory cytokines which induce an inflammatory reaction. The acute inflammatory response causes diarrhea and may lead to ulceration and destruction of the mucosa. The bacteria can disseminate from the intestines to cause systemic disease.

Host Defenses Both nonspecific and specific host defenses are active. Non-specific defenses consist of gastric acidity, intestinal mucus, intestinal motility (peristalsis), lactoferrin, and lysozyme. Specific defenses consist of mucosal and systemic antibodies and genetic resistance to invasion. Various factors affect susceptibility.

Epidemiology Non-typhoidal salmonellosis is a worldwide disease of humans and animals. Animals are the main reservoir, and the disease is usually food borne, although it can be spread from person to person. The salmonellae that cause Typhoid fever and other enteric fevers spread mainly from person-to-person via the fecal-oral route and have no significant animal reservoirs. Asymptomatic human carriers ("typhoid Marys") may spread the disease.

Diagnosis Salmonellosis should be considered in any acute diarrheal or febrile illness without obvious cause. The diagnosis is confirmed by isolating the organisms from clinical specimens (stool or blood).

Control Effective vaccines exist for typhoid fever but not for non-typhoidal salmonellosis. Those diseases are controlled by hygienic slaughtering practices and thorough cooking and refrigeration of food.

INTRODUCTION Salmonellae are ubiquitous human and animal pathogens, and salmonellosis, a disease that affects an estimated 2 million Americans each year, is common throughout the world. Salmonellosis in humans usually takes the form of a self-limiting food poisoning (gastroenteritis), but occasionally manifests as a serious systemic infection (enteric fever) which requires prompt antibiotic treatment. In addition, salmonellosis causes substantial losses of livestock.

Clinical Manifestations Some infectious disease texts recognize three clinical forms of salmonellosis: (1) gastroenteritis, (2) septicemia, and (3) enteric fevers. This chapter focuses on the two extremes of the clinical spectrumgastroenteritis and enteric fever. The septicemic form of salmonella infection can be an intermediate stage of infection in which the patient is not experiencing intestinal symptoms and the bacteria cannot be isolated from fecal specimens. The severity of the infection and whether it remains localized in the intestine or disseminates to the bloodstream may depend on the resistance of the patient and the virulence of the Salmonella isolate.

The incubation period for Salmonella gastroenteritis (food poisoning) depends on the dose of bacteria. Symptoms usually begin 6 to 48 hours after ingestion of contaminated food or water and usually take the form of nausea, vomiting, diarrhea, and abdominal pain. Myalgia and headache are common; however, the cardinal manifestation is diarrhea. Fever (38oC to 39oC) and chills are also common. At least two-thirds of patients complain of abdominal cramps. The duration of fever and diarrhea varies, but is usually 2 to 7 days.

Enteric fevers are severe systemic forms of salmonellosis. The best studied enteric fever is typhoid fever, the form caused by S typhi, but any species of Salmonella may cause this type of disease. The symptoms begin after an incubation period of 10 to 14 days. Enteric fevers may be preceded by gastroenteritis, which usually resolves before the onset of systemic disease. The symptoms of enteric fevers are nonspecific and include fever, anorexia, headache, myalgias, and constipation. Enteric fevers are severe infections and may be fatal if antibiotics are not promptly administered.

Structure, Classification, and Antigenic Types Salmonellae are Gram-negative, flagellated, facultatively anaerobic bacilli possessing three major antigens: H or flagellar antigen; O or somatic antigen; and Vi antigen (possessed by only a few serovars). H antigen may occur in either or both of two forms, called phase 1 and phase 2. The organisms tend to change from one phase to the other. O antigens occur on the surface of the outer membrane and are determined by specific sugar sequences on the cell surface. Vi antigen is a superficial antigen overlying the O antigen; it is present in a few serovars, the most important being S typhi.

Antigenic analysis of salmonellae by using specific antisera offers clinical and epidemiological advantages. Determination of antigenic structure permits one to identify the organisms clinically and assign them to one of nine serogroups (A-I), each containing many serovars (Table 1). H antigen also provides a useful epidemiologic tool with which to determine the source of infection and its mode of spread.

As with other Gram-negative bacilli, the cell envelope of salmonellae contains a complex lipopolysaccharide (LPS) structure that is liberated on lysis of the cell and, to some extent, during culture. The lipopolysaccharide moiety may function as an endotoxin, and may be important in determining virulence of the organisms. This macromolecular endotoxin complex consists of three components, an outer O-polysaccharide coat, a middle portion (the R core), and an inner lipid A coat. Lipopolysaccharide structure is important for several reasons. First, the nature of the repeating sugar units in the outer O-polysaccharide chains is responsible for O antigen specificity; it may also help determine the virulence of the organism. Salmonellae lacking the complete sequence of O-sugar repeat units are called rough because of the rough appearance of the colonies; they are usually avirulent or less virulent than the smooth strains which possess a full complement of O-sugar repeat units. Second, antibodies directed against the R core (common enterobacterial antigen) may protect against infection by a wide variety of Gram-negative bacteria sharing a common core structure or may moderate their lethal effects. Third, the endotoxin component of the cell wall may play an important role in the pathogenesis of many clinical manifestations of Gram-negative infections. Endotoxins evoke fever, activate the serum complement, kinin, and clotting systems, depress myocardial function, and alter lymphocyte function. Circulating endotoxin may be responsible in part for many of the manifestations of septic shock that can occur in systemic infections.

Pathogenesis Salmonellosis includes several syndromes (gastroenteritis, enteric fevers, septicemia, focal infections, and an asymptomatic carrier state) (Fig. 1). Particular serovars show a strong propensity to produce a particular syndrome (S typhi, S paratyphi-A, and S schottmuelleri produce enteric fever; S choleraesuis produces septicemia or focal infections; S typhimurium and S enteritidis produce gastroenteritis); however, on occasion, any serotype can produce any of the syndromes. In general, more serious infections occur in infants, in adults over the age of 50, and in subjects with debilitating illnesses.

Much is now known about the mechanisms of Salmonella gastroenteritis and diarrhea. Figures 2 and 3 summarize the pathogenesis of Salmonella enterocolitis and diarrhea. Only strains that penetrate the intestinal mucosa are associated with the appearance of an acute inflammatory reaction and diarrhea (Fig. 4); the diarrhea is due to secretion of fluid and electrolytes by the small and large intestines. The mechanisms of secretion are unclear, but the secretion is not merely a manifestation of tissue destruction and ulceration. Salmonella penetrate the intestinal epithelial cells but, unlike Shigella and invasive E. coli, do not escape the phagosome. Thus, the extent of intercellular spread and ulceration of the epithelium is minimal. Salmonella escape from the basal side of epithelial cells into the lamina propria. Systemic spread of the organisms can occur, giving rise to enteric fever. Invasion of the intestinal mucosa is followed by activation of mucosal adenylate cyclase; the resultant increase in cyclic AMP induces secretion. The mechanism by which adenylate cyclase is stimulated is not understood; it may involve local production of prostaglandins or other components of the inflammatory reaction. In addition, Salmonella strains elaborate one or more enterotoxin-like substances which may stimulate intestinal secretion. However, the precise role of these toxins in the pathogenesis of Salmonella enterocolitis and diarrhea has not been established.

Normal gastric acidity (pH < 3.5) is lethal to salmonellae. In healthy individuals, the number of ingested salmonellae is reduced in the stomach, so that fewer or no organisms enter the intestine. Normal small intestinal motility also protects the bowel by sweeping ingested salmonellae through quickly. The normal intestinal microflora protects against salmonellae, probably through anaerobes, which liberate short-chain fatty acids that are thought to be toxic to salmonellae. Alteration of the anaerobic intestinal flora by antibiotics renders the host more susceptible to salmonellosis. Secretory or mucosal antibodies also protect the intestine against salmonellae. Animal strains genetically resistant to intestinal invasion by salmonellae have been described. When these host defenses are absent or blunted, the host becomes more susceptible to salmonellosis; factors that render the host more susceptible to salmonellosis are listed in Table 3. For example, in AIDS, Salmonella infection is common, frequently persistent and bacteremic, and often resistant to even prolonged antibiotic treatment. Relapses are common. The role of host defenses in salmonellosis is extremely important, and much remains to be learned.

Contaminated food is the major mode of transmission for non-typhoidal salmonellae because salmonellosis is a zoonosis and has an enormous animal reservoir. The most common animal reservoirs are chickens, turkeys, pigs, and cows; dozens of other domestic and wild animals also harbor these organisms. Because of the ability of salmonellae to survive in meats and animal products that are not thoroughly cooked, animal products are the main vehicle of transmission. The magnitude of the problem is demonstrated by the following recent yields of salmonellae: 41% of turkeys examined in California, 50% of chickens cultured in Massachusetts, and 21% of commercial frozen egg whites examined in Spokane, WA.

The epidemiology of typhoid fever and other enteric fevers primarily involves person-to-person spread because these organisms lack a significant animal reservoir. Contamination with human feces is the major mode of spread, and the usual vehicle is contaminated water. Occasionally, contaminated food (usually handled by an individual who harbors S typhi) may be the vehicle. Plasmid DNA fingerprinting and bacteria phage lysotyping of Salmonella isolates are powerful epidemiologic tools for studying outbreaks of salmonellosis and tracing the spread of the organisms in the environment.

In typhoid fever and non-typhoidal salmonellosis, two other factors have epidemiologic significance. First, an asymptomatic human carrier state exists for the agents of either form of the disease. Approximately 3% of persons infected with S typhi and 0.1% of those infected with non-typhoidal salmonellae become chronic carriers. The carrier state may last from many weeks to years. Thus, human as well as animal reservoirs exist. Interestingly, children rarely become chronic typhoid carriers. Second, use of antibiotics in animal feeds and indiscriminant use of antibiotics in humans increase antibiotic resistance in salmonellae by promoting transfer of R factors.

Salmonellosis is a major public health problem because of its large and varied animal reservoir, the existence of human and animal carrier states, and the lack of a concerted nationwide program to control salmonellae.

Diagnosis The diagnosis of salmonellosis requires bacteriologic isolation of the organisms from appropriate clinical specimens. Laboratory identification of the genus Salmonella is done by biochemical tests; the serologic type is confirmed by serologic testing. Feces, blood, or other specimens should be plated on several nonselective and selective agar media (blood, MacConkey, eosin-methylene blue, bismuth sulfite, Salmonella-Shigella, and brilliant green agars) as well as intoenrichment broth such as selenite or tetrathionate. Any growth in enrichment broth is subsequently subcultured onto the various agars. The biochemical reactions of suspicious colonies are then determined on triple sugar iron agar and lysine-iron agar, and a presumptive identification is made. Biochemical identification of salmonellae has been simplified by systems that permit the rapid testing of 10-20 different biochemical parameters simultaneously. The presumptive biochemical identification of Salmonella then can be confirmed by antigenic analysis of O and H antigens using polyvalent and specific antisera. Fortunately, approximately 95% of all clinical isolates can be identified with the available group A-E typing antisera. Salmonella isolates then should be sent to a central or reference laboratory for more comprehensive serologic testing and confirmation.

Control Salmonellae are difficult to eradicate from the environment. However, because the major reservoir for human infection is poultry and livestock, reducing the number of salmonellae harbored in these animals would significantly reduce human exposure. In Denmark, for example, all animal feeds are treated to kill salmonellae before distribution, resulting in a marked reduction in salmonellosis. Other helpful measures include changing animal slaughtering practices to reduce cross-contamination of animal carcasses; protecting processed foods from contamination; providing training in hygienic practices for all food-handling personnel in slaughterhouses, food processing plants, and restaurants; cooking and refrigerating foods adequately in food processing plants, restaurants, and homes; and expanding of governmental enteric disease surveillance programs.

Recently, The U.S. Department of Agriculture has approved the radiation of poultry to reduce contamination by pathogenic bacteria, e.g. salmonella and campylobacter. Unfortunately, radiation pasteurization has not yet been widely accepted in the U.S. Adoption and implementation of this technology would greatly reduce the magnitude of the salmonella problem.

Vaccines are available for typhoid fever and are partially effective, especially in children. No vaccines are available for non-typhoidal salmonellosis. Continued research in this area and increased understanding of the mechanisms of immunity to enteric infections are of great importance.

Salmonella spp. can infect both warm-blooded and cold-blooded animals. The most common disease caused by Salmonella spp. in animals is diarrhea. Some serotypes produce septicemia (blood poisoning) or abortions in animals. Some animals may be infected and shed the agent in their feces or milk but show no signs of disease. Other animals may get sick then recover but continue to shed the agent even though signs of disease have resolved. The agent may be very difficult to identify due to intermittent shedding. Stress associated with shipment or illness and environmental or nutritional stress may result in shedding the agent or full blown disease. Salmonella may be present in unpasteurized milk, feces, blood or body tissues.

Cleaning and sanitation of animal facilities and equipment decreases the number of bacteria in the animal's environment. Isolation of new animals provides an opportunity to evaluate the animal for presence of this agent and allows an adjustment period for the stress of a new feed, new housing and new neighbors.

Salmonellosis in Humans

Usually human cases are related to contaminated food, especially poultry, eggs, milk and their products. Persons who work with animals may become infected by the agent shed in animal feces. Human Salmonellosis may occur 6-72 hours after ingestion of the agent. Fever, muscle aches, headache and malaise are followed by abdominal pain, nausea, vomiting and diarrhea. The diarrhea may resolve in 2-4 days but some people may continue to shed the bacteria with no signs of disease. Some types of Salmonella can cause septicemia which can result in a disease of longer duration and greater severity.

Salmonellosis is an infection with the bacterium Salmonella. Most persons infected with Salmonella develop diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts 4 to 7 days, and most persons recover without treatment. However, in some persons the diarrhea may be so severe that the patient needs to be hospitalized. In these patients, the Salmonella infection may spread from the intestines to the blood stream, and then to other body sites and can cause death unless the person is treated promptly with antibiotics. The elderly, infants, and those with impaired immune systems are more likely to have a severe illness.

Salmonella describes several different kinds of bacteria. These bacteria typically infect the gut of a host animal. Physical illness may or may not result from the infection. When physical illness does occur from Salmonella infection it is referred to as Salmonellosis. With high levels of Salmonella exposure and low levels of cattle resistance, any one of the many kinds of Salmonella can cause Salmonellosis. There are, however, some strains of Salmonella that are more likely to cause illness. Salmonella typhimurium is one such strain. Salmonella typhimurium is the most common type of Salmonella found in Michigan dairy cattle, cows and calves. It is also the most likely type of Salmonella to result in physically ill cattle.

Salmonellosis has numerous possible symptoms. Symptoms include diarrhea, bloody stool, fever, dehydration, anorexia/emaciation, rapid breathing, unusual or foul odor stool, sloughing of skin from extremities, and sudden death. Treatment of Salmonellosis can be costly, impractical, and in some instances ineffective. An on-farm outbreak of Salmonellosis is costly because of veterinary expenses, reduced animal performance, involuntary culling, death loss, and lost reputation as a healthy herd.

Cattle with Salmonellosis are not the only Salmonella infected cattle of concern. Some animals may harbor Salmonella in their gut and show no symptoms. These "carriers" can be shedding Salmonella into the environment in their manure for extended periods of time without giving any indication of an infection. Carriers may not become ill because of low levels of exposure and high tolerance; however, they can still transmit the disease to other animals. Salmonella can remain prevalent and undetected in a dairy herd until a stress lowers animal tolerance. A stress of any kind can potentially compromise the immune system and permit Salmonellosis to occur.

Salmonella most commonly causes illness in calves; however, it can effect cattle of all ages. It is usually passed from animal to animal by fecal-oral contact. On-farm contamination of feed is the most common source of Salmonella infection. Given a cool, damp, and dark environment, Salmonella can survive outside of a host animal for days, weeks, and even months. Manure and other organic materials can support the bacteria while it is waiting to be ingested by an unsuspecting new host.

How prevalent is Salmonella?

Salmonella is more prevalent in dairy cattle than one might realize. A 1991-92 study conducted by the U.S.D.A. National Animal Health Monitoring System (NAHMS) found that 20.5 of every 1,000 or 2 percent of dairy calves in the Midwest tested positive for Salmonella. A NAHMS study conducted in 1996 revealed that during the warmer, moister months of the year 11 percent of all cows on dairy farms in the United States were shedding Salmonella. The number of positive cows was less than 2 percent during winter months. The 11 percent of dairy cows shedding during warmer, moister months represented 38.2 percent of U.S. dairy farms. Cattle shedding during the winter months represented 21.1 percent of dairy farms.

The 1996 NAHMS study showed a fairly strong correlation between Salmonella shedding and herd size. In reality, the correlation may be to the number of purchased cattle rather than herd size. Michigan is currently undergoing a tremendous number of herd expansions, meaning a tremendous number of cattle purchases. At the same time, very few Michigan dairy farms are following recommended biosecurity guidelines when purchasing cattle. Without adequate preventive steps, acquiring more cattle equals acquiring enormous risk of infectious disease. Thus, it is likely that the incidence of Salmonella outbreaks on Michigan dairy farms is on the increase. Salmonella incidence will continue to grow until all Michigan dairy farmers, not just those who are expanding, tighten on-farm biosecurity.

How do I prevent a Salmonella outbreak on my farm?

Biosecurity! Biosecurity! Biosecurity! This word has been beaten to death over the past year, but it has been abused with good reason. A few simple practices in biosecurity can save you from an on-farm health disaster. The old cliché still holds true, "An ounce of prevention is worth a pound of cure."

Total biosecurity involves many areas of management from vaccination programs to farm visitor management. Unfortunately, an effective vaccine against Salmonella in adult cows is not likely in the near future, so preventing animal exposure is the key. Preventing exposure implies that you must know how Salmonella might get onto your farm.

There are two basic ways Salmonella can get onto your farm, animal transmission and inanimate transmission:

Animal Transmission:

· Incoming cattle – Whether you are purchasing cattle or just temporarily housing cattle for someone else, you must be certain that they are Salmonella-free. A veterinarian can have the animals tested; however, repetitive tests of every animal over an extended period of time are required. Repetitive fecal sampling is the best way of ensuring Salmonella-free animals, but this can be a slow and bothersome process. Fortunately, there is another way, know the health history of the source herd(s). This alternative is not foolproof, but it does greatly reduce the risk of introducing many diseases, not just Salmonella.

Oftentimes, the biggest hurdle in knowing the health history of an incoming animal’s source herd is identifying the source herd. Knowing where an animal comes from is simple, if you are buying directly from the dairy producer who bred the animal.

Knowing where an animal has been becomes much more difficult, if not impossible, when purchasing animals through sale barns or cattle brokers. Buying from a sale barn or broker usually means that the animals have been exposed to a "community" handling facility, barn, and trailer. These facilities and equipment have been used and manured on by hundreds, if not thousands, of animals from who knows where. With the contaminated facilities and trailer, it is almost impossible to completely realize to what pathogens, including Salmonella, the animals have been exposed

Once you know the source herd(s), get permission from the owner(s) to talk with the respective farm’s veterinarian. Assuming that the veterinarian has a valid working relationship with the source herd, he or she should be able answer your questions about the current and past health status of that herd.

· Other resident animals – Salmonella not only resides in the fecal material of cattle but of many animals. Birds, rodents, and cats are of primary concern on dairy farms. Contamination of feed with fecal material from any one of these other animals could potentially introduce Salmonella into your herd.

Inanimate Transmission:

Since Salmonella can survive outside of a host animal in organic material for quite some time, one can easily envision how Salmonella might move from farm to farm without animal movement. Any inanimate object with a little organic material on it can transport the Salmonella bacterium.

Think about it! What might be able to pick-up Salmonella at one farm and transport it to another farm? Who might inadvertently bring Salmonella onto your farm?

Since you cannot keep all of these people off of your farm, what can you do about it? You may not be able to keep the people away, but you can prevent them from bringing unwanted guests, like Salmonella, with them.

In February 1995, the New Mexico Department of Health (NMDOH) was notified of cases of salmonellosis in two persons who had eaten beef jerky. An investigation by the New Mexico Environment Department determined that these cases were associated with beef jerky processed at a local plant. An investigation by NMDOH identified 91 additional cases. This report summarizes the investigation of this outbreak.

On January 26, 1995, two men presented to the emergency department of a local hospital after onset of diarrhea and abdominal cramps. On January 24, the men had purchased and consumed carne seca, a locally produced beef jerky. Cultures of leftover beef jerky and stool obtained from one patient grew Salmonella. On February 7, NMDOH identified both isolates as Salmonella serotype Montevideo.

NMDOH initiated efforts to determine whether other cases of salmonellosis associated with beef jerky had occurred. On February 8, NMDOH issued a news release advising the public not to eat the implicated brand of beef jerky and to contact the local health department if illness had occurred after eating the product. Cases also were identified through a review of NMDOH records for isolates matching those identified in jerky samples. A confirmed case of beef jerky-related salmonellosis was defined as isolation of Salmonella from a stool sample obtained from a person who had consumed the implicated jerky. A probable case was defined as onset of diarrhea, abdominal cramps, vomiting, and/or nausea in a person who had consumed the implicated jerky.

Illness in 93 persons met the probable or confirmed case definitions. 111 persons reported purchasing the jerky at the local processing plant and eating the jerky during January 21-February 7; onset of symptoms occurred during January 22-February 11 (Figure 1). Incubation periods for most (89%) persons were less than or equal to 3 days. The median age of ill persons was 22 years (range: 2-65 years); 56 (60%) were male. Symptoms of the 93 persons included diarrhea (93%), bloody diarrhea (13%), abdominal cramps (87%), headache (74%), fever (61%), vomiting (43%), and chills (40%). The median duration of illness was 7 days (range: 1-40 days). Five persons (5.4%) were hospitalized.

Of the 93 cases, 40 were culture-confirmed. From the stool samples of these 40 ill persons,three Salmonella serotypes were isolated: Salmonella Typhimurium (31 persons), Salmonella Montevideo (12), and Salmonella Kentucky (11). Stool samples from 12 persons yielded two serotypes, and the sample from one patient contained all three serotypes. Samples of leftover beef jerky were obtained from five ill persons and from the manufacturer; 11 of the 12 samples tested contained one or more of the three Salmonella serotypes isolated from the patients. Each of the Salmonella Typhimurium isolates obtained from 31 persons with culture-confirmed cases and from the beef jerky were the same uncommon phenotypic variant.

The processing plant that manufactured the contaminated beef jerky was inspected by state authorities on January 31. However, because the plant was not in production, processing-stage temperatures could not be obtained. The owner of the plant described the processing to include placement of slices of partially frozen beef on racks in a drying room at 140 F (60 C) for 3 hours, then holding the meat at 115 F (46 C) for approximately 19 hours; however, temperatures of the meat were never measured. After processing, the jerky was placed in uncovered plastic tubs for sale to the public. The plant owner, who performed all the work in the plant, denied a history of recent gastrointestinal illness but declined to provide a stool specimen. The plant voluntarily closed permanently on February 10. Salmonella was not isolated from environmental swabs taken from 20 surfaces within the plant on February 20.

British cattle farmers have enough to worry about with bovine spongiform encephalopathy (BSE) and the recent outbreak of E. coli O157:H7 in Scotland. Now, a dramatic increase in Salmonella typhimurium isolates that are resistant to 5 or more antibiotics is adding to their problems. Since 1993, 65% of all Salmonella species cultured from cattle in the UK have been identified as a strain of S. typhimurium DT104, resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline (1). Some strains are also resistant to trimethoprim, spectinomycin and/or ciprofloxacin (2). Antibiotic-resistant DT104 were first observed in 1984 but remained an infrequent isolate until 1990. An increasing percentage of S. typhimurium isolates from humans in England and Wales have also been identified as DT104. This strain accounted for 70% (2700) of all reports of S. typhimurium during the first 8 months of 1996 and for 55%, 52%, and 32% of isolates in 1995, 1994, 1993, respectively. Although S. enteriditis PT4 continues to be the most commonly isolated species of Salmonella, S. typhimurium DT104 is now in second place (3). Foodborne Salmonella infections are usually not severe. However, 34 of 83 DT104 cases studied in a 1993 epidemiological study required hospitalization and 10 died. The very young and the very old were most susceptible to serious complications (4).

Foodborne transmission of DT104 has been documented for several outbreaks; suspected vehicles included roast beef, ham, pork sausage, salami sticks, "cooked meats," chicken legs, and unpasteurized milk (5–9). Analyses of 786 samples of fresh and frozen sausages in England in 1994 demonstrated that 17% were contaminated with Salmonella spp., including S. typhimurium DT104 (10). This indicates that these bacteria are commonly present in some types of meats and pose a significant risk if such foods are not cooked and handled properly.

In contrast to S. enteritidis, which is associated primarily with poultry and eggs, DT104 is most commonly detected in cattle. Some sheep, pigs, goats, chickens, and turkeys are also infected. A majority of recent bovine salmonellosis cases investigated in England were caused by DT104, and 15 of 16 new outbreaks of bovine salmonellosis in Scotland, in March 1996, were caused by DT104 (1,11). These bacteria cause diarrhea in cattle and may persist in the animals for up to 6 months after recovery. A number of farm families appear to have acquired DT104 infections while caring for sick farm animals (12,13). Household pets may also be a source of infection. Of 110 Salmonella spp. isolated from sick house cats in England in 1991–1994, 40 were S. typhimurium DT 104 resistant to 5 antibiotics (14).

Where has this multiply resistant strain of S. typhimurium come from? Plasmids containing drug resistance genes are well known in bacteria and can be transferred among different species of enteric bacteria. However, most of the genes coding for resistance to these antibiotics in DT104 are located on chromosomal, rather than plasmid, DNA. Some interesting recent research reported a relatively high frequency of hypermutable strains among pathogenic E. coli and Salmonella spp. (15). When compared to standard strains of these bacteria, isolates associated with some foodborne outbreaks produced mutant cells resistant to rifampin at a 1000-fold greater frequency. These increased rates of mutation were associated with the presence of mutant genes coding for enzymes involved in the recognition of foreign DNA and DNA repair. Defects in one of these repair systems, the methyl-directed mismatch repair, were found in many pathogenic mutator strains. Hypermutability will, of course, produce many nonviable cells but also greatly increases the likelihood that advantageous mutations will occur. Such mutations in DNA repair systems also facilitate the acquisition of plasmid DNA containing antibiotic resistance genes from other species of bacteria.

Under the selective pressure of antibiotics, the growth of resistant organisms is favored. Some evidence indicts the increased use of veterinary drugs as a factor in the dramatic increase in drug resistance. Resistance to ciprofloxacin in DT104 isolates has increased from 1% in 1994 to 6% in 1995, coincident with the licensing of this drug for veterinary use in the UK in 1994 (2). Resistance to trimethoprim (present in 27% of DT104 isolates) may have been acquired in response to the use of this drug to combat bovine infections with DT104 resistant to other drugs. Surveys of S. typhimurium isolates from cattle and humans in Australia (16), France (17), Hong Kong (18), and Spain (19) all reveal an increased incidence of resistance to multiple antibiotics in this organism.

What is salmonellosis? Salmonellosis is a bacterial infection that generally affects the intestinal tract and occasionally the bloodstream. It is one of the more common causes of gastroenteritis with several thousand cases occurring in New York State each year. Most cases occur in the summer months and are seen as single cases, clusters or outbreaks.

Who gets salmonellosis? Any person can get salmonellosis, but it is recognized more often in infants and children.

How are salmonella bacteria spread? Salmonella are spread by eating or drinking contaminated food or water or by contact with infected people or animals.

What are the symptoms of salmonellosis?

Diarrhea, fever, vomiting

How soon after exposure do symptoms appear? The symptoms generally appear one to three days after exposure.

Where are salmonella found? Salmonella are widely distributed in our food chain and environment. The organisms often contaminate raw meats, eggs, unpasteurized milk and cheese products. Other sources of exposure may include contact with infected pet turtles, pet chicks, dogs and cats.

For how long can an infected person carry the salmonella germ? The carrier stage varies from several days to many months. Infants and people who have been treated with oral antibiotics tend to carry the germ longer than others.

Do infected people need to be isolated or excluded from work or school? Since salmonella are in the feces, only people with active diarrhea who are unable to control their bowel habits (infants, young children, certain handicapped individuals, for example) should be isolated. Most infected people may return to work or school when their stools become formed provided that they carefully wash their hands after toilet visits. Food handlers, health care workers and children in day care must obtain the approval of the local or state health department before returning to their routine activities.

What is the treatment for salmonellosis? Most people with salmonellosis will recover on their own or require fluids to prevent dehydration. Antibiotics and antidiarrhea drugs are generally not recommended for typical cases with intestinal infections.

Salmonella is the genus name of a number of bacteria commonly associated with food poisoning from contaminated or undercooked foods, and salmonellosis is the disease the bacteria can cause. In food-related cases, most people suffer from gastroenteritis, often experiencing vomiting, fever, diarrhea, and cramps. For high-risk individuals, such as those with weakened immune systems, those taking antibiotics, pregnant women, the elderly, and children under 5, salmonellosis may be even more devastating, leading to blood infections, meningitis, abortion, and death.

In a case reported by the New York Health Department in 1995, a pregnant woman with fever and diarrhea went into preterm labor and delivered a baby who died 12 hours later. Follow-up blood samples of mother and child, in conjunction with samples from the family's pet iguana, tested positive for the salmonella strain associated with reptiles.

"Like most other reptiles, iguanas carry salmonella in their intestinal tracts," says Patrick L. McDonough, Ph.D., assistant director of bacteriology at Cornell University's College of Veterinary Medicine in New York. "The bacteria are 'shed' periodically in the animals' feces, and that's how the bacteria gets on the animals' skin, their cages, and other materials they touch."

An influx of cases at Cornell University since 1993 has prompted officials to warn owners that good hygiene is essential to prevent the spread of salmonella.

"Wash your hands with warm, soapy water immediately after handling iguanas or their cage litter, and before touching food or anyone else," McDonough says. He adds that while researchers once believed salmonellosis was transmitted primarily through direct contact with reptiles, it is now known that the bacteria need only be present on surfaces or on the hands of others to infect individuals indirectly.

In one such case, 20 patients were diagnosed with the disease within eight days of visiting a Komodo dragon exhibit at a Colorado zoo. According to Joseph Madden, Ph.D., strategic manager for microbiology at FDA's Center for Food Safety and Applied Nutrition, zoo officials believe that the dragons had, while being moved to their cages, licked several handrails at the zoo, and those areas were then touched by zoo visitors who subsequently ate lunch without washing their hands.

An Outbreak Revisited

In the early 1970s, FDA banned the distribution and sale of baby turtles with shells 4 inches in length or less after a quarter million infants and small children were diagnosed with having turtle-associated salmonellosis. The agency believed that turtles larger than 4 inches did not pose the same threat since youngsters would not likely try to fit them into their mouths. CDC estimated that in 1973, pet turtles accounted for 14 percent of the salmonella-caused illnesses in the United States.

But the FDA-imposed ban allows for some exceptions. Turtles still can be exported to other countries and sold to experts for bona fide scientific, educational and exhibition purposes. Selling turtles to pet stores is not considered a bona fide purpose.

Janet McDonald, a public affairs specialist with FDA's San Francisco district office, believes that since the turtle issue is so old, people have forgotten that they are still illegal in the United States.

"We're still seeing sales of baby turtles and iguanas at flea markets and street fairs, and owners need to be aware that these pets can transmit disease, particularly to very young children because of their hand-to-mouth activity," she said. "The sale of reptiles is definitely on the rise."

Darrell Lee, an FDA computer expert who works with McDonald, saw firsthand that the sale of baby turtles is "a very brisk business" on a recent visit to Oakland's Chinatown. According to Lee, youngsters were peddling turtles and their cages at a rate of five every 15 minutes.

"It was like a street corner sale generating a huge profit," Lee recalled. "Here they were, young children selling them to other kids with no adults around."

But some public officials and responsible members of the scientific profession now believe that educating people rather than regulating reptiles would be more effective in controlling the spread of salmonella infection. According to several state health departments, there has been considerable effort to educate pediatricians, hospitals, clinics, and pet shop owners.

Robert and Lisa Wenner of Brunswick, Md., couldn't agree more about educating the public. The couple, with the help of their two young sons, operate an iguana rescue mission from their home and won't even consider adopting out these animals until they are convinced that prospective pet owners know and understand the risks associated with owning one.

"I recommend people buy a book about iguanas which tells all about the risk from exposure to salmonella," Robert says. And that's after he subjects them to a rigorous question-and-answer session to determine if indeed they do have a thorough understanding of the hazards involved. In the two years since the Wenners have owned their seven iguanas as personal pets, they say they have experienced no disease-related problems, which they attribute to the meticulous hygiene they insist their family members practice.

"We bathe our iguanas every day and disinfect our tub afterward each and every time," Robert says. And a trip to the sink to wash up with an antibacterial soap by all family members after each handling goes without saying. As to the three 4-foot-tall cages that house their pets, Lisa adds, "You have to commit yourself to cleaning them every single day."

But not all experts agree that bathing iguanas everyday is good practice. Victoria Hampshire, V.M.D., a veterinarian in the carnivore and ungulate unit at the National Institutes of Health, cautions against daily, harsh scrubbing of the animals because of the likelihood of dry skin and fungal infections. She believes that washing the iguana everyday should not be necessary if the animal has clean water and an adequate UV light source. A safe compromise, she says, would be to squirt down or mist the iguana daily.

A kennel technician for the Frederick County Animal Control, Lisa Wenner is all too aware of the hazards associated with animals and contracted diseases in general. However, not one case of reptile-associated salmonellosis has been reported since she began working there over six years ago. Wenner believes that the staunch efforts made by local veterinarians and health department officials to inform the public through literature and public forums are key to preventing the spread of the disease.

"What we've learned from the vets is that as long as you keep the reptiles clean and you clean up yourself and your surroundings after handling, you will minimize the risk of infection with salmonella," she says. Additionally, in the one and a half years since the Wenners have adopted out 15 iguanas through their rescue mission, no cases of the infection have been reported.

One of several types of bacteria which can cause food poisoning (salmonellosis) if ingested in large numbers. It is found in the intestinal tract of animals, birds, insects, reptiles, seafood, and people. The bacteria can easily be passed from the intestinal tract to the hands and onto food.

There is a great deal of confusion over the naming of Salmonella strains (even the people who work on Salmonella are confused!) but in essence, the strains which we will deal with here are generally different serovars of Salmonella enterica. This means that they all belong to the genus Salmonella, a division that groups similar, though not identical bacteria together. These bacteria are named after the scientist who discovered them, Dr. Daniel Salmon. The majority of the components of these bacteria are identical, and at the DNA level, they are between 95% and 99% identical. (As a comparison E. coli and Salmonella, which are closely related to each other, are about 60-70% identical at the DNA level). As their name suggests Salmonella enterica are involved in causing diseases of the intestines (enteric means pertaining to the intestine). The three main serovars of Salmonella enterica are Typhimurium, Enteritidis, and Typhi. Each of these is discussed further below. These distinctions are are designed to help scientists distinguish similar bacteria from each other in papers and when discussing the genetics. j, i. To complicate matters, serovars of Salmonella enterica can be subgrouped even further by "phage type". This technique uses the specificity of phage to differentiate between extremely closely related bacteria. Often these bacteria are indistinguishable by other means, and indeed, the reasons for the differences in phage specificity are often not known.

Although the inside of the egg was once considered almost sterile, Salmonella enteritidis (Se) has been found recently inside a small number of eggs (much less than 1%). If an egg does contain Se, the numbers in a freshly laid egg probably will be small and, if the eggs are properly refrigerated, will not multiply enough to cause illness in a healthy person.

The majority of salmonellosis outbreaks have been attributed to foods other than eggs—chicken, beef, and fish—to human carriers, and through them, utensils and other foods during preparation. Of the outbreaks involving eggs, almost all have occurred in the foodservice sector and have been the result of inadequate refrigeration and insufficient cooking.

Se will not grow at temperatures below 40ºF. and is killed at 160ºF., known as the danger zone, are ideal for rapid growth.

Chicken, turkey, pork, beef, and other meat and poultry products are important sources of protein and other nutrients. Unfortunately, these foods--like eggs, raw milk, and all raw foods of animal origin--may also carry salmonella and other bacteria. The good news is that these bacteria don't have to cause illness. Routine food safety practices can destroy salmonella and other bacteria.

The Food Safety and Inspection Service (FSIS) oversees the processing of meat and poultry from the time animals enter the slaughter plant until packaged products leave the plant. FSIS also conducts a comprehensive food safety education program, including a toll-free hotline. FSIS requires manufacturers of raw and partially pre-cooked meat and poultry products to provide safe food handling labels to remind consumers about thorough cooking and safe handling of meat and poultry products.

Consumers have a right to meat and poultry that is as free as possible of bacteria. However, after more than 20 years of research, it is still economically impossible to produce "salmonella-free" raw meat and poultry. With or without a breakthrough, good sanitation and careful food handling will always be necessary to prevent bacteria on raw products from causing illness--just as toothbrushing is necessary to prevent other bacteria from causing dental cavities.

What is salmonella? This FSIS backgrounder answers common questions about salmonella and offers some tips for safe handling of meat and poultry to prevent food-borne illness.

The salmonella family includes about 2,000 different strains of bacteria, but only 10 strains cause most reported salmonella infections. Strains that may cause no symptoms in animals can make people sick, and vice versa. A salmonella bacterium is a one-celled organism that can't be seen, touched or tasted. The bacteria are common in the intestinal tracts and waste of livestock, poultry, dogs, cats, rats, and other warm-blooded animals.

What is salmonellosis? Salmonellosis, or a salmonella infection, is the illness that can occur if live salmonella bacteria enter the body--usually through food. Most reported outbreaks of food-borne illness are caused by bacteria, and salmonellosis is the most common bacterial food-borne illness. Salmonellosis is usually preventable.

How can salmonella bacteria on raw meat and poultry make people sick? First, "food abuse" allows bacteria to survive and often to multiply. For example, if the meat knife is ued to cut the salad lettuce without first being washed, the lettuce can be contaminated by any bacteria on the meat. The person who eats the salad then also eats the bacteria.

Next, if the bacteria survive the stomach acid, they reproduce themselves in the small intestine. Once cell becomes two, two become four, four become sixteen, and so on. When there are "enough" bacteria, they cause a salmonella infection.

How many bacteria does it take to make people sick? There is no exact number, but the more bacteria consumed, the more likely a person is to get sick. Healthy adults have eaten food containing millions of bacteria without getting sick. Other people have gotten sick from as few as 10 bacteria in their food.

What are the symptoms of salmonellosis? According to the Centers for Disease Control, stomach pain occurs within 6 to 48 hours after the food was eaten. Most people get diarrhea, and many people have upset stomachs, chills, fever, or headache. Most people feel better within 3 to 5 days. Many persons with salmonellosis may believe they have the flu and may never see a doctor.

How many people get sick from salmonellosis? At least 40,000 salmonella infections are reported every year, but experts believe that between 400,000 and 4 million persons each year actually contract salmonellosis.

How does the doctor know a person has salmonellosis? The only way to tell for sure is to conduct laboratory tests on the stools of the person who got sick, a process that takes several days.

How many people die from salmonellosis? Salmonella infections can be life-threatening for the very young, the very old and for persons already weakened by other serious diseases, such as AIDS. Reports show about 2 deaths for every 1,000 known cases of salmonellosis, but experts believe that about 500 persons each year actually die from salmonella infections.

Salmonella enterica serovar Typhi. (Also called Salmonella Typhi or abbreviated to S. Typhi) This bacterium is the causative agent of typhoid fever. Although typhoid fever is not widespread in the United States, it is very common in under-developed countries, and causes a serious, often fatal disease. The symptoms of typhoid fever include nausea, vomiting, fever and death. Unlike the other Salmonella discussed below, S. Typhi can only infect humans, and no other host has been identified. The main source of S. Typhi infection is from swallowing infected water. Food may also be contaminated with S. Typhi, if it is washed or irrigated with contaminated water. Salmonella enterica serovar Typhimurium (Also called Salmonella Typhimurium or abbreviated to S. Typhimurium) Until recently the most common cause of food poisoning by Salmonella species was due to S. Typhimurium. As its name suggests, it causes a typhoid-like disease in mice. In humans S. Typhimurium does not cause as severe disease as S. Typhi, and is not normally fatal. f, g, b. The disease is characterized by diarrhea, abdominal cramps, vomiting and nausea, and generally lasts up to 7 days. Unfortunately, in immunocompromized people, that is the elderly, young, or people with depressed immune systems, Salmonella infections are often fatal if they are not treated with antibiotics.

What foods are most likely to make people sick? Foods don't make people sick--bacteria do. Any raw food of animal origin--meat, poultry, raw milk, fish, and shellfish--may carry salmonellae. The bacteria can survive to cause illness if these specific foods are not thoroughly cooked. The bacteria can also cause illness if they contaminate any other food that comes in contact with the raw food, either directly or byway of dirty hands or dirty equipment. Salmonellosis is a world-wide, food- chain problem that can't be "blamed" on any one food.

Wouldn't less bacteria on animals mean less human illness? FSIS and the National Academy of Sciences agree with this logical assumption. However, there will always be some risk of bacterial contamination on raw foods of animal origin. So, food safety will always be necessary to prevent bacteria on raw foods from causing illness.

CLEAN IT. Salmonella bacteria can survive in water, soil, and on the kitchen counter, so sanitation can make a big difference-- especially in preventing bacteria that could be on raw products from contaminating other foods. (This is called cross- contamination.)

Wash your hands frequently with SOAP and water for at least 20 seconds -- after you use the bathroom, before you start food preparation, before you start working with a new food or a new tool, when you finish food preparation, and before you serve food.

Prevent cross-contamination. Never let raw meat and poultry, or their juices, come in contact with cooked meat or any other food -- raw or cooked.

If you use a dishcloth for cleaning kitchen surfaces, switch to a clean one after you work with raw meat or poultry. Choose a type that will stand up to laundering in hot water and bleach. Otherwise, use paper towels and throw away after use.

Cut raw meat or poultry on an acrylic cutting board that is thoroughly cleaned after each use. Use that favorite (but porous) wooden one only for cutting bread or vegetables.

Wash cutting boards, knives, counter, and other implements with detergent and hot water immediately after you use them with raw meat and poultry.

After washing and rinsing equipment and counters, professional food service workers also sanitize and rinse them. Consumers who want to sanitize implements after washing can use a solution of 1 teaspoons household bleach in 1 quart of water, followed by cold water rinse. (Note: Sanitizing doesn't work on dirty surfaces, so clean them first.)

Serve cooked meat and poultry on clean plates. When you replenish the banquet, replenish the serving plates. Don't put grilled meat or poultry back on the plate with raw juices.

Keep pets away from food, and away from cooking and eating surfaces and equipment.

COOK IT. Salmonellae -- however many there are -- do not survive when beef or pork is cooked to an internal temperature of at least 160 degrees F, or when poultry is cooked to 185 degrees F. (Some experts believe that this country's passion for rare beef explains why beef -- which carries very low levels of salmonella bacteria -- is involved in more reported salmonellosis outbreaks than poultry.) Always cook meat and poultry thoroughly, and be just as careful when microwaving as when using traditional ovens.

Use a Meat thermometer to check "doneness." If meat is too thin for a thermometer, follow the recipe and cook till the juices have no pink.

Never interrupt cooking--it's a "half-baked idea" that can make you sick. If thawing foods in the microwave, cook them immediately.

If reheating leftovers, cover and reheat thoroughly to 165 degrees F just in case bacteria survived in the food during refrigeration or freezing. Let sauces and gravies reach a rolling boil.

Don't store the latecomer's cooked meat and poultry dinner in an off or warm oven. Hold the food above 140 degrees F. (But, within 2 hours after doing, refrigerate the food.)

COOL IT. Refrigeration and even freezing do not kill all salmonella or other bacteria, but proper cooling can usually prevent salmonellae from multiplying.

Refrigerate raw meat and poultry as soon as possible after you take it out of the grocery meat case.

Refrigerate food containing cooked meat or poultry within 2 hours after cooking.

Refrigerate or freeze cooked meat or poultry casseroles in covered shallow pans rather than deep pots. Leave space around the containers to let cold air circulate.

Never thaw frozen and poultry on the kitchen counter. Thaw it in the refrigerator or, if you are in a hurry, in a bag under could running water.

Remember that refrigeration or freezing cannot be counted on to kill many salmonella bacteria. It can't "fix" a mistake such as leaving cooked turkey at room temperature for more than 2 hours-- it can only postpone the risk of illness. If in doubt, throw the food out.

A Guide to Salmonella Prevention/Control:

1. Never eat or put anything on your mouth when working with reptiles.

2. Never clean cages on the kitchen or anywhere you prepare food for human consumption.

3. Always wash your hands with a disinfectant soap after handling your animals.

4. Have you veterinarian examine sick animals, or perform necropsies (animal autopsies) on animals which die suddenly, to check for Salmonella.

5. Make it a practice to keep cages clean. Proper husbandry and hygiene are fundamental to keeping healthy animals and minimizing disease transmission.

6. Young children and people under medical care from their physicians (such as antibiotic therapy, and immunosuppressive drugs, etc.) should not handle reptiles and amphibians.

7. If you feel that you have been exposed to the Salmonella bacteria, or if you have any questions regarding human Salmonellosis, you are encouraged to see your family physician immediately.

The number of outbreaks linked to Salmonella contamination of shell eggs has steadily declined from about 50 to 60 a year down to 30 in 1995, according to Dr. John Mason, former director of the United States Department of Agriculture (USDA) Salmonella enferitidis (SE) Control Program tracking SE outbreaks and their causes. According to Dr. Mason, the risk of contracting egg-related salmonellosis is extremely low for healthy individuals. "There is one outbreak for every 2 billion eggs consumed," he said.

Salmonella enterica serovar Enteritidis (Also called Salmonella Enteritidis or abbreviated to S. Enteritidis). In the last 20 years or so, S. Enteritidis has become the single most common cause of food poisoning in the United States. S. Enteritidis causes a disease almost identical to the very closely related S. Typhimurium. S. Enteritidis is particularly adept at infecting chicken flocks without causing visible disease, and spreading from hen to hen rapidly. Many people have blamed the recent increase in the rise of S. Enteritidis infections on the use of mass production chicken farms. When tens or hundreds of thousands of chickens live together, die together, and are processed together a Salmonella infection can rapidly spread throughout the whole food chain. A compounding factor is that chickens from a single farm may be distributed over many cities, and even states, and hence Salmonella infections can be rapidly dispersed through millions of people. How does Salmonella cause disease? After Salmonella is eaten it passes through the stomach to the intestine. Here, it binds to the wall of the intestine, and through some special proteins that it makes in response to the particular conditions in the intestine it actually penetrates the barrier between us and the outside. f, a, j, k, b. Once it has gained access to our insides, it is taken to the liver or spleen. For most other bacteria, this journey would kill them, however Salmonella has evolved mechanisms to prevent our immune system from doing its job efficiently. In the liver, the Salmonella can grow again, and be released back into the intestine. Of course, not all of the Salmonella pass through the intestinal wall, and many of them are expelled from the intestine in the diarrhea.

"The decrease can be attributed to better handling and proper cooking of eggs by food service establishments," said Dr. Mason. "Consumers can virtually eliminate the risk at home by cooking eggs properly." According to the American Egg Board, eggs should be cooked until the white is firm and opaque and the yolk is thickened, no longer runny. It is not necessary to hard cook the yolk. Salmonella is destroyed at a temperature of 140 degrees F for 3.5 minutes. The yolk begins to get thick at a temperature of 148 degrees F.

To minimize the risk of egg-related Salmonellosis, consumers should follow these practices recommended by USDA, the Food and Drug Administration and American Egg Board:

--> Buy refrigerated grade A or AA eggs with clean uncracked shells. Discard eggs that are cracked or leaking.

--> If any shell falls into the egg when cracking it open, remove shell piece with a clean utensil.

--> Keep eggs refrigerated at or below 40 degrees F in the original carton in the coldest section of the refrigerator, usually the center shelf, not the door.

--> When refrigerating a large amount of a hot egg-rich dish or leftover, divide it into several small shallow containers so it will cool quickly.

--> Cook scrambled eggs or omelets until there is no visible liquid egg remaining.

--> Avoid keeping raw or cooked eggs and egg-containing foods out of the refrigerator for more than two hours, including time for preparing and serving.

--> Use cooked recipes for Hollandaise and similar sauces, homemade ice cream and egg nog.

--> Make sure recipes like French toast, crab cakes, Monte Cristo sandwiches, stuffing, and pasta dishes like lasagna are cooked all the way through (160 degrees F. at the center).

--> Wash hands, utensils, equipment, and work areas with hot soapy water before and after they come in contact with raw eggs.

--> When serving infants, pregnant women, the elderly, the ill, or the immuno-compromised, cook all egg dishes thoroughly or use a pasteurized egg product.

The egg industry has voluntarily instituted quality assurance and sanitation measures to control Salmonella at the farm level. Research supported by the egg industry, academia, FDA, and USDA is addressing the causes of Salmonella and the best way to control the problem.

What is salmonellosis? Salmonellosis refers to a group of infectious diseases caused by exposure to Salmonella bacteria. This group includes food poisoning (gastroenteritis), blood poisoning (bacteremia), and typhoid fever, each caused by a different type of Salmonella bacterium.

Food poisoning is the most common type of salmonellosis in this country.

How does it occur? Salmonella bacteria can be found in milk and dairy products, eggs, poultry, and processed meats. You can spread the disease after handling food or utensils contaminated with the bacteria. Carriers of salmonellosis and household pets such as dogs, cats, and turtles can also spread the disease.

You will get sick with this particular food poisoning 8 to 48 hours after eating contaminated food.

What are the symptoms? Symptoms of food poisoning include:

diarrhea (which may contain blood), lasting 3 to 5 days

fever and chills

nausea and vomiting

abdominal cramps. How is it diagnosed? The doctor will ask about your symptoms, examine you, and take samples of your blood, stool, and urine. The samples are sent to a lab for testing.

How is it treated? The doctor will examine you to find out whether your abdomen is tender and whether you have a fever. He or she will check for dehydration (severe loss of body fluids), which could require hospitalization.

Treatment involves controlling your symptoms. If you are undernourished, severely ill, very young, or have sickle cell disease, the doctor may prescribe an antibiotic. Otherwise, antibiotics are not routinely prescribed because they may prolong the carrier state.

Treatment for blood poisoning also includes treatment of any skin sores.

How long will the effects last? Salmonellosis usually lasts 3 to 5 days. You can continue to carry the disease after you've been infected, whether or not you have symptoms. However, this isn't usually a permanent condition.

How can I take care of myself? It is particularly important to follow the treatment plan your doctor prescribes. Stay warm. Ask your doctor if you can take aspirin, acetaminophen, or ibuprofen to control your fever. (Anyone under age 21 who may have a viral illness should not take aspirin because aspirin increases the risk of Reye's syndrome.) Keep a daily record of your temperature.

For diarrhea, let your bowel rest by drinking only clear liquids such as water, juice, weak tea, and bouillon. You may also suck on Popsicles. It is important to drink often so you don't get dehydrated. Suck on ice chips if you feel too nauseated to drink anything. Do not eat solid foods because they can cause cramps.

How can I help prevent salmonellosis? Salmonella bacteria are killed by cooking food thoroughly. Thaw and cook meats especially thoroughly. Wash your hands with soap and very warm water before and after handling food.

Have proper immunizations against typhoid fever before traveling outside this country or if a member of your household carries the disease. The vaccine is given in two doses 4 or more weeks apart, and a booster shot is given every 3 years.

Unintended Aid to Salmonella? The Washington Post, Compiled from reports by Rob Stein January 3, 2000

In the 1980s, health officials in Europe and the United States realized there had been a sharp increase in food poisoning caused by a type of salmonella bacterium found in chickens, eggs and egg products. The upsurge caused concern that perhaps modern farming techniques were to blame.

Now scientists have proposed a new theory: A more virulent strain of salmonella was given a chance to flourish in poultry after less serious forms were killed off with antibiotics.

Andreas J. Baumier of the Texas A&M University Health Science Center in Texas and colleagues reviewed the scientific literature and concluded that a strain of salmonella called S. enteritidis flourished after strains called S. pullorum and S. gallinarum were eradicated from domesticated flocks of birds beginning in the 1930s. The birds then may have become infected with the S. enteritidis strain from mice and rats making their way into henhouses.

"The increased incidence of salmonellosis in humans may have been caused by S. enteritidis filling the ecological niche vacated by eradication of the avian pathogens," the researchers wrote in the Jan. 7 issue of Science, which was released last week.

Of 390 persons registered at the conference, 86 (22%) returned questionnaires by August 12. A questionnaire was returned by the index patient who made the initial call to CDC but not by the four other persons he contacted who were passengers on the same flight. Six (7%) of the 86 respondents reported having diarrhea (three or more loose stools in a 24-hour period) during the period beginning 12 hours after the conference started and ending 5 days after the conference ended (July 20 to 26). Among questionnaire respondents, only the index patient was diagnosed with salmonellosis. Three respondents had taken the initially suspect flight. Illness was not associated with taking the same flight as the index patient (p = 0.20, Fisher's Exact Test, 2-tailed).

To further investigate the reports of diarrhea, we interviewed the six persons who reported diarrheal illness by questionnaire, as well as the four persons initially contacted by the index patient who had not completed questionnaires. This group included the two persons with known Salmonella infection, of whom one had completed a questionnaire and one had not. Seven of the other eight persons had mild, nonspecific symptoms of less than 2 days' duration; the onset dates of their illnesses spanned a 5-day period, and none sought medical attention. Because few conference attendees or flight passengers became ill with symptoms suggestive of salmonellosis during a likely period, we thought that an airplane- or conference-associated outbreak was improbable. By September 9, questionnaires were returned by 156 (40%) of the conference attendees. No additional cases of diarrhea were reported, confirming our initial conclusion that the Salmonella infections were not associated with the flight or the conference.

Subsequent investigation focused on meals that the two persons with salmonellosis shared outside the conference and ultimately revealed the source, a restaurant in Baltimore. In late July 1994, the Maryland Department of Health and Mental Hygiene received reports that Salmonella, serogroup C1, had been isolated from five other persons who visited Baltimore around the time of the conference. Two persons from one family had driven to Baltimore on July 17, eaten only at one restaurant, then returned to their home state of Pennsylvania. Three persons in a second family, from a different part of Pennsylvania, ate at the same Baltimore restaurant on July 21 during a vacation trip. The Salmonella isolates from members of both families were initially misidentified as other serogroup C1 serotypes. They were retested because of this outbreak and were confirmed as S. Norwich. The two conference attendees with S. Norwich infection also ate at the implicated restaurant on July 21. No single menu item had been eaten by all ill persons. In response to a complaint by the first family, the restaurant had been inspected by the local health department; multiple violations of food safety regulations were found. S. Norwich was isolated from a stool specimen from an employee who reported a diarrheal illness beginning on July 22 and who ate the restaurant's food. In the month following the inspection of Restaurant A and subsequent corrective action, no further cases of S. Norwich were reported to PHLIS from Maryland or Pennsylvania.

E-mail can expedite questionnaire distribution, especially when the population of interest is on one network. The computer system used to send the e-mail message in this outbreak was not linked to individual conference attendees; therefore, we could not evaluate the rates at which individual attendees obtained and responded to the message. If we had been able to reach attendees directly, our response rate may have been higher, and we would have been able to send additional messages to nonresponders. In the future, when outbreaks occur among persons accessible by e-mail, it may be possible to evaluate strategies to improve response rate and to compare the effectiveness of the delivery of questionnaires by e-mail and by more traditional means.

This outbreak illustrates the usefulness of rapid electronic communication in a public health setting. Isolation of a rare Salmonella serotype and national electronic reporting to PHLIS assisted in the detection and investigation of a widely dispersed multistate outbreak of salmonellosis. Without the national Salmonella serotyping system, the outbreak would not have been recognized. Questionnaires were distributed rapidly by e-mail; the utility of this method is likely to increase as more people become accessible by e-mail. Fax provided a means for respondents to return questionnaires quickly. Continued on-line analysis of surveillance data with PHLIS confirmed that the outbreak was controlled. Rapid communication between public health workers in Maryland and Pennsylvania and at CDC was also essential. The usefulness of electronic communication is not limited to outbreak investigation. New technologies will undoubtedly continue to be useful in addressing emerging public health problems.

Because of reports of increasing numbers of illnesses associated with consumption of raw sprouts, the U.S. Food and Drug Administration is advising all persons to be aware of the risks associated with eating raw sprouts (e.g., alfalfa, clover, radish). Outbreaks have included persons of both genders and all age categories. Those persons who wish to reduce the risk of foodborne illness from sprouts are advised not to eat raw sprouts.

This advice is particularly important for children, the elderly, and persons with weakened immune systems, all of whom are at high risk of developing serious illness due to foodborne disease. People in high risk categories should not eat raw sprouts.

This advisory is updated from a previous health advisory issued August 31, 1998, and is based on additional information from clover and alfalfa sprout-associated salmonellosis outbreaks from January through May 1999. Two outbreaks were associated with clover sprouts: one occurred in California in May and involved approximately 30 cases; a second outbreak in Colorado from March through May involved approximately 70 cases. In addition, from January through March an outbreak of salmonellosis affecting approximately 85 people occurred in Oregon, Washington, and California and was associated with the consumption of alfalfa sprouts.

In regions with poor sanitation, these bacteria can than survive in the soil or in rivers and infect the next person, cow, chicken or mouse that comes along. Where do I get Salmonella from? Well, you can try the Salmonella Genetic Stock Center. Most infections with Salmonella are traced back to dairy, poultry and meat products, but Salmonella can grow on just about any food. Chickens and eggs are particular high risk foods. Salmonella is one of the most common enteric (intestinal) infections in the U.S. In some states (e.g. Georgia, Maryland) it is the most common, and overall it is the second most common foodborne illness (usually slightly less frequent than a Campylobacter infection). The reported incidence of Salmonella illnesses are about 17 cases per each 100,000 persons.Salmonella is a type of bacteria that causes typhoid fever and many other infections of intestinal origin. Typhoid fever, rare in the U.S., is caused by a particular strain designated Salmonella typhi. But illness due to other Salmonella strains, called "salmonellosis," is common in the U.S. Today, the number of known strains (technically termed "serotypes" or "serovars") of this bacterium total over 2,300. Over 40,000 actual cases are reported and confirmed yearly in the U.S.2 As only about 3% of Salmonella cases are officially reported nationwide,3 and many milder cases are never diagnosed, the true incidence is undoubtedly much higher. It is more common in the warmer months of the year. j, b, i, h, a. Approximately 500 to 1,0004 persons, or 31% of all food-related deaths2 are caused by Salmonella infections in the U.S. every year. Salmonella is an infection caused by a gram-negative bacillus, a germ of the Salmonella genus. Infection with these bacteria may involve only the intestinal tract, or may spread from the intestines to the blood stream and then to other body sites. The source of infection is contaminated food or water, or close contact with other human beings carrying the infection.

Since 1995, raw sprouts have emerged as a recognized source of foodborne illness in the United States. These illnesses have involved the pathogenic bacteria Salmonella and E. coli O157. Alfalfa and clover sprouts have been involved most often, but all raw sprouts may pose a risk.

The sprout industry has been working in cooperation with government, academia, and other industry segments to enhance the safety of its product. These efforts have focused primarily on seed treatment strategies, good manufacturing practices, and sanitation.

"Despite all these efforts to make raw sprouts safer, we continue to receive reports of illnesses associated with raw sprouts. Consumers need to understand that, at this time, the best way to control this risk is not to eat raw sprouts," said Jane E. Henney, MD, FDA Commissioner.

Although infections with Salmonella and E. coli O157 can cause serious illness, the illness is generally self-limiting in most healthy adults. However, an E.coli O157 infection can lead to hemolytic uremic syndrome with resultant kidney failure or death in children, and equally serious complications in the elderly. Salmonella infections can cause serious illness in children, the elderly, and the immune compromised. Healthy persons infected with these bacteria experience diarrhea, nausea, abdominal cramping, and fever for several days.

From September 19 through October 10, 1994, a total of 80 confirmed cases of Salmonella enteritidis (SE) infection were reported to the Minnesota Department of Health (MDH); in comparison, 96 cases were reported statewide during all of 1993. Cases were characterized by diarrhea, abdominal cramps, and fever. Recent increases in SE cases also were reported from South Dakota (14 cases during September 6-October 7, compared with 20 cases during all of 1993) and Wisconsin (48 cases during September 6- October 7, compared with 187 during all of 1993). This report summarizes preliminary findings from the outbreak investigation.

On October 5 and 6, to assess potential risk factors for infection, the MDH conducted a case-control study of 15 cases and 15 age- and neighborhood-matched controls. A case was defined as culture-confirmed SE in a person with onset of illness during September. Eleven case-patients (73%) and two controls (13%) reported consumption of Schwan's ice cream within 5 days of illness onset for case-patients and a similar period for controls (odds ratio=10.0; 95% confidence interval=1.4-434.0).

On October 7 and 9, the MDH issued press releases informing the public of this problem and advising persons who had been ill since September 1 and who had consumed Schwan's ice cream to contact the health department. During October 8-11, a total of 2014 persons who had consumed suspected products and had been ill with diarrhea contacted the MDH by telephone. Samples of ice cream from households of ill persons grew SE.

Ill persons reported eating all types and flavors of ice cream products produced at the Schwan's plant in Marshall, Minnesota, including ice cream, sherbet, frozen yogurt, and ice cream sandwiches and cones; these products had production dates in August and September. The implicated products are distributed nationwide, primarily by direct delivery to homes, and are sold only under the Schwan's label. Investigations to examine the extent and causes of the outbreak are under way.

On November 28, 1995, the county coroner's office notified the Clark County Health District in Las Vegas, Nevada, about a death suspected to have resulted from a foodborne disease. This report summarizes the investigation of the outbreak of gastroenteritis among persons who attended a Thanksgiving dinner. The investigation documented Salmonella serotype Enteritidis (SE) infection associated with eating improperly prepared turkey and stuffing containing eggs and emphasizes the need to use a meat thermometer to ensure complete cooking of turkey and stuffing.

During November 25-28, 1995, all six persons who attended a Thanksgiving dinner at a private home on November 23 and a seventh person who on November 25 ate food remaining from the dinner had onset of abdominal cramps, vomiting, and diarrhea. Two persons were hospitalized because of dehydration; a third person was found comatose at home and died from severe dehydration and sepsis. Stool cultures obtained from three persons, including the decedent, yielded SE phage type 13a. Turkey and stuff ing were the only foods eaten by all seven ill persons. No leftover food was available for culture.

The Clark County Health District interviewed the ill persons (including the cook) to obtain details about the preparation and cooking of the turkey and stuffing. On November 22, a 13-pound frozen turkey was thawed for 6 hours in a sink filled with cold water. After thawing, the packet of giblets (heart, liver, and gizzard) was removed, and the turkey was stored in a refrigerator overnight. However, on November 23, parts of the turkey were noted to be frozen. The turkey was filled with a stuffing made from bread, the giblets, and three raw eggs, and then placed for 1 hour in an oven set at 350 F (177 C). The setting was lowered to 300 F (149 C) while the turkey cooked for an estimated additional 4 hours. The turkey was removed from the oven when the exterior had browned. A meat thermometer was not used. The stuffing was removed immediately and was served with the turkey. After the outbreak, health officials tested the oven set at 300 F (149 C) and found the temperature to be 350 F (176 C).

Foodborne infections cause an estimated 6.5 million cases of human illness and 9000 deaths annually in the United States (1). Salmonella is the most commonly reported cause of foodborne outbreaks, accounting for 28% of such outbreaks of known etiology and 45% of outbreak-associated cases during 1973-1987 (2). During 1985-1992, state and territorial health departments reported 437 Salmonella enteritidis (SE) outbreaks (Table 1), which accounted for 15,162 cases of illness, 1734 hospitalizations, and 53 deaths. This report describes three SE outbreaks in California during a 4-month period in 1993.

Outbreak 1: Los Angeles County

In January 1993, routine surveillance for salmonellosis identified four unrelated persons with gastroenteritis and stool cultures yielding SE who recently had eaten at a local restaurant; one person had been hospitalized. The mean period from eating at the restaurant to onset of illness was 20 hours (range: 11-24 hours); duration of symptoms ranged from 1 to 14 days. All four isolates were phage type 13a and plasmid profile type 2 (36 and 3.7 megadalton plasmids), an unusual pattern among SE isolates. All four ill persons reported having eaten an egg-based dish (omelette, scrambled eggs, or egg salad) at the restaurant during December 26, 1992-January 6, 1993.

An investigation by the Los Angeles County Department of Health Services involved the four reported cases, five well meal companions, and 100 restaurant patrons identified through credit card receipts; two additional cases were identified. A case was defined as onset of di