Salmonellosis outbreak due to chicken contact leading to a foodborne outbreak associated with infected delicatessen workers

Abstract

Salmonella is the most common bacterial cause of foodborne outbreaks in the United States. Starting in June 2007, investigation of a cluster of Salmonella Montevideo cases with indistinguishable pulsed-field gel electrophoresis (PFGE) patterns resulted in the identification of an outbreak associated with contact with chickens purchased from a single hatchery. Nine Minnesota cases from May through August 2007 were part of this outbreak. Cases with the outbreak PFGE pattern of Salmonella Montevideo continued to occur in Minnesota after August, but none of these cases reported chicken contact. The majority of these cases resided in the same town in rural Minnesota. Routine interviews revealed that all cases from these counties purchased groceries from the same local grocery store, with two specifically reporting consuming items from the grocery store delicatessen in the week before illness. As a result, an investigation into the delicatessen was initiated. Illness histories and stool samples were collected from all delicatessen employees, and food and environmental samples were collected. None of the employees reported experiencing recent gastrointestinal symptoms, but the outbreak PFGE subtype of Salmonella Montevideo was identified from stool from two food workers. Food and environmental samples collected tested negative for Salmonella. One of the positive employees reported having chickens at home, but the animals did not test positive for Salmonella. The positive food workers were excluded from work until they had two consecutive negative stool cultures for Salmonella. There was no evidence of ongoing transmission thereafter. This was an outbreak of Salmonella Montevideo infections that began as an animal-contact-associated outbreak which subsequently resulted in a foodborne outbreak associated with infected food workers. These outbreaks illustrate the complex epidemiology of salmonellosis.