METHODS: A confirmed case was defined as an individual with consumption of pork at the pig roast and laboratory confirmed infection with Salmonella I 4,5,12:i:-, PFGE pattern JP6X01.1314 or JP6X01.2311 in 2013 and Salmonella Typhimurium, I 4,12:i:1,2, PFGE pattern JPXX01.0065 in 2015. A probable case for both outbreaks was someone who consumed the pork and experienced diarrhea, but did not have laboratory testing performed. Case control studies of ill and well pig roast attendees were conducted, using interviews in 2013 and an online questionnaire in 2015. The Rhode Island State Health Laboratory tested human isolates and leftover pork specimens in both outbreaks. In 2015, CDC tested human and pork isolates for antimicrobial resistance and performed whole genome sequencing. Traceback investigations and farm inspections were conducted by the Rhode Island Center for Food Protection (CFP). Slaughterhouse inspections and environmental sampling were conducted by CFP in 2013 and USDA in 2015.
RESULTS: Exposure information was obtained on 16 ill and 10 well individuals in 2013, and 20 ill and 7 well individuals in 2015. In both outbreaks, 100% of ill individuals consumed roasted pork, making odds ratio calculation impossible. In 2015, the host of the pig roast reported that the pork was served undercooked, reaching only 130°F. In both outbreaks, concordant human and pork isolates tested positive for Salmonella, and matched by PFGE. Isolates were subtyped as Salmonella I 4,5,12:i:- in 2013 and Salmonella Typhimurium, I 4,12:i:1,2 in 2015. While the 2015 outbreak strain did not match the whole hog outbreak in Washington State during the same time period, it displayed the same pattern of antimicrobial resistance. Environmental samples from the slaughterhouse, farm, and feed tested negative in 2013, while samples from the slaughterhouse tested positive for Salmonella St. Paul in 2015. No major sanitary violations were noted at the slaughterhouse or farm in either outbreak.
CONCLUSIONS: In both years, the source of illness was consuming pork. While this explains the cause of the outbreaks, it does not explain how the hogs became infected with Salmonella. Outbreaks related to whole hogs have become increasingly common in recent years. With two such outbreaks in the country’s smallest state within two years, Rhode Island’s experience should be considered a sentinel event.