Multiple-serotype Salmonella gastroenteritis outbreak after a reception — Connecticut, 2009

In September 2009, the Connecticut Department of Public Health (DPH) identified an outbreak of Salmonella gastroenteritis among attendees at a reception. A case-control study and environmental and laboratory investigations were conducted. Nine case-patients and 14 control subjects were identified. Potato salad consumption was strongly associated with illness (odds ratio [OR] = 84.0). During the investigation, food service workers were observed to have bare-handed contact with ready-to-eat food. Five case-patients and one asymptomatic food service worker had stool samples positive for Salmonella species. Two Salmonella serotypes were identified, Salmonella enterica serovar Schwarzengrund and Salmonella enterica serovar Typhimurium variant O:5–, including coinfection in one case-patient and one food service worker. The isolates of each respective serotype (S. Schwarzengrund and S. Typhimurium variant O:5–) had indistinguishable pulsed-field gel electrophoresis (PFGE) patterns. Potato salad was the likely source of the outbreak but the contamination mechanism is unclear. Control measures included exclusion of the food service worker with Salmonella-positive stool from the restaurant until two consecutive stool samples yielded no bacterial growth. Standard public health laboratory practices in Connecticut and testing techniques used specifically during this investigation led to the rapid identification of the two serotypes. Multiple-serotype Salmonella outbreaks might occur more frequently than recognized; knowledge of all Salmonella serotypes involved in an outbreak might help implicate the outbreak source, define the scope of the outbreak, and determine the selection of appropriate control measures.