Salmonellosis is a common enteric disease caused by rod-shaped, gram-negative bacteria. The name is derived from the American veterinary surgeon, Daniel A. Salmon, who described Salmonella choleraesuis as the cause of hog cholera in 1885. Since then over 2,200 Salmonella serotypes have been described; each is distinguished by its unique combination of cell wall, flagella, and capsular antigens. Many serotypes are further subdivided, usually for epidemiological studies, by their sensitivity to standard sets of bacteriophages (phage typing), and DNA fingerprinting methods. Salmonella are found in the intestinal tract of animals and birds, including domestic species (e.g., cattle, poultry), wild animals, and pets. Most human infections are caused by a few serotypes, commonly S. typhimurium and S. enteritidis. In most countries that keep national statistics, the majority of human cases are due to only five to ten common serotypes.
Salmonellosis is characterized by diarrhea, headache, abdominal pain, fever, and vomiting, beginning 6 to 72 hours (usually 6 to 36 hours) after infection. Healthy people normally recover within a week. Some individuals, however, are more susceptible to serious illness (see Table 1), and there is increasing evidence of longer-term sequelae occurring in a small proportion of cases.
Specific Salmonella serotypes are adapted to specific hosts, in which they usually cause septicaemia. For example, Salmonella typhi, is the cause of typhoid in man. Human infection is linked to a diverse variety of foods, possibly contaminated by animal or human feces during slaughter or during cultivation, harvesting, and preparation. Foods most commonly linked to illness include those of animal origin, such as meat products, unpasteurized milk, poultry, and eggs; foods contaminated during cultivation or preparation including vegetables, salads, fruit; and, less commonly, processed foods such as chocolate and snack products. Human infection has also been linked to exotic pets such as turtles, reptiles, and small mammals. People recovering from infection or with mild symptoms excrete salmonellae in their feces, and they may become a source of infection for others. Person-to-person spread is a particular risk where hygiene standards are difficult to maintain, as in institutions, day-care facilities, nursing homes, and households with ill individuals.
Most cases are apparently sporadic, though outbreaks occurring in the general population are not unusual and may be linked to a social event or institution such as a hospital or nursing home, or large-scale catering issues such as hotels, restaurants, and canteens. More rarely, large national and international outbreaks have been associated with manufactured or processed food products—in 1998 over 800 cases of S. enteritidis in Canada were associated with a pre-packed lunch product. Probably the largest recorded Salmonella outbreak affected an estimated 185,000 individuals who drank improperly pasteurized milk in the United States in 1985. It is recognized that even in countries which keep national statistics most cases are not reported. For example, only an estimated 1
|Individuals Susceptible to Severe Disease or Complications|
|Susceptible Individuals||Possible Complication|
|source: Courtesy of author.|
|Very young and elderly.||Rapid and severe dehydration.|
|Individuals with low stomach acid.||Increased susceptibility to infection.|
|Individuals with cancers and depressed immune systems, including HIV-infected persons.||Increased risk of Salmonella septicaemia.|
|Individuals with sickle-cell disease.||Risk of internal abscesses and bone-joint infections.|
percent of cases in the United States are reported, and the estimated morbidity and economic burden is high. Current public health concern centers around the emergence of multiple antibiotic resistant salmonellae, which make serious illness, such as blood infection, difficult to treat.
Paul N. Sockett
(see also: Food-Borne Diseases )
Old, D. C. (1992) "Nomenclature of Salmonella." Journal of Medical Microbiology 37:361–363.
Roberts, J. A., and Sockett, P. (1994) "The Socioeconomic Impact of Human Salmonella Enteritidis Infections." International Journal of Food Microbiology 21:117–129.
Rodrigue, D. C.; Tauxe, R. V.; and Rowe, B. (1990). "Increase in Salmonella Enteritidis : A New Pandemic?" Epidemiology and Infection 1:21–27.
Saeed, A. M.; Gast, R. K.; Potter, M. E.; and Wall, P. G., eds. (1999). Salmonella enteritidis serovar enteritidis in Humans and Animals: Epidemiology, Pathogenesis, and Control. Ames, IA: Iowa State University Press.
Sockett, P. N. (1991). "The Economic Implications of Human Salmonella Infection." Journal of Applied Bacteriology 71:289–295.
Salmonellosis (sal-mo-nel-O-sis) is a gastrointestinal disease earned by bacteria called Salmonella. This type of bacterium usually is found in foods such as poultry, milk, and eggs from infected animals.
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Food borne illness
Salmonellosis is an illness caused by Salmonella bacteria that affects the intestine, usually resulting in diarrhea. In some people, the infection spreads to the bloodstream and other areas of the body and can be life-threatening unless they receive prompt treatment.
Salmonellosis, named after the American scientist Daniel Salmon, is one of the most common causes of food poisoning in the United States. Each year, about 40,000 cases of salmonellosis are reported to the U.S. Centers for Disease Control and Prevention, and up to 4 million additional cases may go unreported. About 1,000 people die each year of complications related to salmonellosis. Infants, the elderly, and people whose immune systems* are weakened are most vulnerable to severe infection.
- * immune system
- is the system that defends the body against disease.
In the United States, people usually get salmonellosis from eating or drinking contaminated food, most often raw milk or undercooked poultry and poultry products such as eggs. Undercooked ground beef or other meat can also cause salmonellosis. In some cases, food can be contaminated by the people handling it. Salmonellosis can also be spread through the stools of some pets, especially reptiles and pets with diarrhea.
A different species of Salmonella bacteria causes typhoid fever, a serious disease common in developing countries in Latin America, Africa, and Asia. Typhoid fever is spread by food and water contaminated with the bacteria. Clean water, treated (pasteurized) milk, and effective sewage systems have made typhoid fever rare in the United States and other developed countries.
The symptoms of salmonellosis include diarrhea, stomach cramps, pain, fever, headache, nausea, and vomiting. They occur within 12 to 48 hours of eating or drinking contaminated food.
Salmonellosis is diagnosed through stool cultures from people with symptoms of the infection. Salmonella infections usually run their course without treatment in a few days to a week after an unpleasant period of vomiting and diarrhea. Health care professionals suggest that people drink lots of fluids and eat a bland diet while they recover from salmonellosis. Sometimes the symptoms create other problems, such as dehydration*. In those cases, people may need to go to the hospital to receive replacement fluids through their veins (an “IV”). Antibiotics may be used if the infection spreads beyond the intestine, but salmonellosis is often resistant to drugs.
- * dehydration
- is the loss of fluid from the body faster than it can be replaced.
Thorough cooking (until poultry or meat, especially ground beef, is no longer pink and eggs are no longer runny) and regular hand washing (after using the bathroom, and between handling raw meat and other foods) are the main ways to prevent salmonellosis. Only pasteurized dairy products that have been kept refrigerated should be used. Raw meat or eggs should especially be avoided.
U.S. Centers for Disease Control and Prevention, 1600 Clifton Road N.E., Atlanta, GA 30333. This U.S. agency helps control communicable, carrier-borne, and occupational diseases and prevent disease, injury, and disability. A fact sheet on salmonellosis is available on its website. Telephone 404-639-3534 http://www.cdc.gov/ncidod/dbmd/diseaseinfo/salmonellosis_g.htm
U.S. National Institute of Allergy and Infectious Diseases, Office of Communications and Public Liaison, National Institutes of Health, Building 31, Room 7A-50, 31 Center Drive, MSC 2520, Bethesda, MD 20892-2520. This government biomedical research center posts a fact sheet on salmonellosis and other foodborne diseases on its website. Telephone 301-496-4000 http://www.niaid.nih.gov/factsheets/foodbornedis.htm