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Background
Salmonella are a group of bacteria that can cause diarrheal illness in people. This constitutes a major public health burden and represents a significant cost to society in many countries. There are more than 2,000 types of Salmonella, with Salmonella Typhimurium and Salmonella Enteritidis most commonly encountered globally. Salmonella are inhabitants of the feces of many types of animals. According to a Centers for Disease Control and Prevention estimate, 1.4 million cases of salmonellosis occur each year in the United States.1 Salm-Surv is a global effort devoted to foodborne disease surveillance and outbreak detection; Salmonella is its original focus because of the significant role this organism plays in foodborne disease worldwide.1
Symptoms and Disease Process
The disease caused by Salmonella is generally called salmonellosis. Symptoms of salmonellosis typically appear 12 to 36 hours after contaminated food is eaten, and last for one to four days. Symptoms include diarrhea, abdominal pain, chills, fever, vomiting, dehydration and headache. In some cases, individuals recovering from salmonellosis may continue to shed Salmonella in their feces for weeks to months after symptoms have disappeared.
Primary Routes of Transmission
The primary reservoirs of Salmonella are the intestinal tracts of infected domestic and wild animals, thus foods of animal origin such as poultry, eggs, beef and pork are often sources. People can also carry Salmonella in their intestinal tracts. Salmonella is passed in the feces and can remain alive outside of the host animal for possibly years. Many foods, including produce, can become contaminated by the unclean hands of a food handler, by cross-contamination during preparation, or by irrigation or preparation of foods with contaminated water. Contaminated ice has also caused salmonellosis outbreaks. Other foods identified as vehicles for Salmonella transmission include coconut, chocolate, peanut butter, yeast, and soy. Flour may be contaminated with Salmonella; however, proper cooking inactivates the organism.
Outbreaks have occurred from foods contaminated with just a few cells, especially when the cells are protected in the digestive tract by high levels of fat in the food. Other foods involved in outbreaks may require higher contamination rates to result in illness. The infectious dose depends on the age and health of the host, strain differences among the members of the genus, and protective effects of the food.
Control
Control of Salmonella focuses on adequate cooking of potentially contaminated foods. Cross-contamination control is also essential for cooked and ready-to-eat foods. Sanitary practices and adequate hand washing are critical in this area. Good Agricultural Practices are also essential for produce safety. The organism can grow over a temperature range of 7-46°C, water activity as low as 0.94, and pH from 4.4-9.4.2
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References
1 Mead, P.S., Slutsker, L., Dietz, V., McCaig, L.F., Bresee, J.S., Shapiro, C., Griffin, P.M., Tauxe., R.V. (1999). Food-Related Illness and Death in the United States. Emerg, Inf. Dis.5(5):607-25. http://www.cdc.gov/ncidod/eid/vol5no5/mead.htm
2World Health Organization Global Salm-Surv Progress Report 2000-2005. (1.84 MB) 
3International Commission on Microbiological Specifications of Foods. Microorganisms in Foods 5, Microbiological Specifications of Food Pathogens. Blackie Academic and Professional, New York. 1996.
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