Salmonella Typhimurium Outbreak Associated with Restaurant Cross-Contamination and Household Environmental Contamination, Kentucky, 2013

BACKGROUND: While salmonellosis outbreaks related to contaminated food are common, secondary and tertiary infections from contact with case patients or their homes is rarely reported. In September 2013, the Kentucky Department for Public Health and local health departments investigated an outbreak of SalmonellaTyphimurium infections that included cross-contamination of foods in a restaurant as the primary source of infection and environmental contamination in the home as a secondary source of additional infections.

METHODS: Case patients were interviewed with a standard foodborne illness questionnaire. Answers were analyzed to identify common exposures and establish a case definition.  Active surveillance was enhanced in area hospitals and the state public health laboratory to rapidly identify and prioritize Salmonella isolates from the impacted regions for serotyping and pulsed-field gel electrophoresis (PFGE) analysis.  An environmental assessment was conducted and food samples collected for laboratory analysis from a restaurant common to several case patients (Restaurant A).

RESULTS: We established a case definition as: Any individual from a 3-county area in Kentucky with illness onset of 09/08/2013 or later with vomiting and/or diarrhea who tested positive for Salmonella Typhimurium, PFGE pattern JPXX01.0146.  A total of 16 individuals were identified as part of this outbreak. Fourteen cases reported eating at Restaurant A and were considered primary cases.  A secondary case with household exposure to two primary cases and a tertiary case with household exposure to the secondary case were also identified through patient interviews and confirmed by PFGE analysis of isolates.  All of the primary cases reported exposure to Restaurant A, with 71.4% consuming chicken and 7.14% consuming beef.  Laboratory testing of clinical isolates identified Salmonella Typhimurium PFGE Xbal pattern JPXX01.0146 and BlnI pattern JPXA26.1074 as the primary outbreak strain. Two food samples collected at Restaurant A yielded Salmonella Typhimurium indistinguishable from the clinical isolates by XbaI and Blnl.  The environmental assessment at Restaurant A identified significant violations in food storage and food handling practices that provided opportunities for cross-contamination.  Environmental contamination at the home of two primary cases, poor hand hygiene, and inadequate cleaning practices were suspected to enable transmission and infection in the secondary and tertiary cases.

CONCLUSIONS: Although many salmonellosis outbreaks are a result of foods consumed in a restaurant, environmental contamination in the homes of infected individuals or direct contact with case patients may further spread the infections.  Proper food handling practices, hand hygiene, and appropriate cleaning methods must be emphasized to case patients to prevent further transmission.