Contaminated tomatoes and infected food service workers are suspected to be behind the Salmonella outbreak that has sickened 171 people in 19 states.
DNA fingerprinting has identified Salmonella enterica serotype Typhimurium as the cause of the outbreak according to a statement released by the Centers for Disease Control and Prevention (CDC), in a press release yesterday. The symptoms of the disease are fever and non bloody diarrhea that may extend up to a week. Clinical data of 73 patients has revealed 14 hospitalized and no deaths.
The CDC reported that the outbreak appeared to be over although the hunt for the source of the outbreak may take days to weeks. The agency said, "At this time, few new cases are being detected, and there is little evidence of continuing risk to the public."
The CDC detected the outbreak about 2 weeks ago through a national database that identifies patterns in food borne illness reports. Cases in the outbreak have been reported since Sep 1 with most of the affected states being in the eastern half of the nation.
According to Carlota Medus, PhD, an epidemiologist with the Minnesota Department of Health in St. Paul, samples from 14 patients in Minnesota matched the outbreak strain on pulsed-field gel electrophoresis (PFGE). Minnesota cases mainly occurred between Sep 12 and Oct 13 and when a pattern was noticed they contacted the CDC.
Medus said that a case-control study in Minnesota appeared to suggest that the contamination source may be tomatoes and that the five cases appeared to be linked to the same fast-food restaurant. She said, "Our study is pretty small, though. It would be nice to have more supporting information, so it's a little too soon to say."
Foodborne disease expert Craig W. Hedberg, PhD, an associate professor of environmental health sciences at the University of Minnesota School of Public Health in Minneapolis, called the outbreak fairly significant in its size and scope. "This outbreak is most likely due to tomatoes, and many cases were probably exposed through restaurants," he said.
According to Hedberg a major concern in restaurant-related outbreaks of salmonellosis is the role of infected food handlers in spreading the disease. He said that food service workers can become ill from eating the contaminated product and then expose customers to the disease when they are still shedding the organism and don't use proper hygiene practices.
Medus was the lead author of a study in the August issue of the Journal of Food Protection where the role of food service workers in restaurant-related Salmonella outbreaks in Minnesota between 1995 and 2004 was tracked. The researchers found that 129 of 1,033 food workers tested positive for Salmonella with about half of them reporting no recent gastrointestinal illness. Bacterial shedding lasted about 30 days in the workers who reported symptoms, but averaged only 3 days in those who didn't.
The authors of the report concluded that the duration of Salmonella outbreaks in restaurants suggests that there existed an ongoing contamination reservoir with infected food workers being a likely source of disease transmission.
Hedberg, a coauthor of the report, asserted that infected food workers, as secondary transmission sources, can increase the size and duration of the outbreaks. He said, "Restaurants should be stepping up surveillance for illnesses in their food workers," and also said that restaurants should make sure that food workers who have gastrointestinal illnesses are evaluated and treated.