Released October 31, 2006

Outbreak Investigation, October 2006

Salmonellosis Outbreak Investigation

The Centers for Disease Control and Prevention (CDC), in collaboration with state departments of health and the Food and Drug Administration (FDA), is investigating an outbreak of infections caused by a type of Salmonella called Salmonella Typhimurium. This infection has no relationship to typhoid fever, which is caused by another organism. Salmonella Typhimurium typically causes an illness with fever and non-bloody diarrhea which commonly resolves after about one week. This illness is different from that caused by E. coli O157:H7, which produces bloody diarrhea, severe cramps, and in some persons, severe kidney disease. PulseNet, the network of public health laboratories that performs molecular subtyping (“DNA fingerprinting”) on bacteria that cause foodborne illnesses, has identified a specific strain of Salmonella Typhimurium that has caused this outbreak. Cases caused by the specific strain have been detected regularly at low frequency (average, 86 cases per year) for the past 5 years, indicating the presence of this strain at low levels in the environment and the food chain. The outbreak has involved 171 cases of infection by this strain in 19 states reported since September 1, 2006. The median age of patients is 36 years, and 59% are female. As with most infections by Salmonella, most patients had a febrile diarrheal illness. Of 73 patients for whom clinical data has been reported, 14 (19%) were hospitalized; there have been no deaths reported. At this time few new cases are being detected, and there is little evidence of continuing risk to the public.

CDC and its public health partners are vigorously working to identify the specific contaminated food or foods that caused this outbreak. Outbreaks from a widely distributed contaminated food cause cases to be scattered across the country, and the identity of the contaminated food is often not readily apparent. In outbreaks like this one, identification of the contaminated food requires conducting detailed standardized interviews with recovering case-patients and with non-ill members of the public (“controls”) to compare the foods they had eaten. Using statistical methods, the contaminated food is identified as one eaten more commonly by case-patients than the controls. This statistically-based method of identifying contaminated foods is routinely supplemented and confirmed by laboratory testing of foods. The process is labor intensive and may require days to weeks. As soon as the contaminated food is identified, if there is evidence of ongoing risk, public health officials can advise the public to avoid it, and remove the food from the marketplace.

Precise information on avoiding infection with the outbreak strain of Salmonella will be provided by CDC as soon as the contaminated food(s) is identified. Members of the public are urged to follow several practices for reducing the risk of foodborne illness. See Salmonellosis Frequently Asked Questions for information. Persons with immune-compromising conditions should consider following specific precaution.

Date: October 31, 2006
Content source: Coordinating Center for Infectious Diseases / Division of Bacterial and Mycotic Diseases


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