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BACKGROUND: Salmonella Blockley is a rare serotype in the U.S. Only two clusters have been reported in PulseNet’s history, and no source was identified for either. On July 17, the Iowa Department of Public Health (IDPH) identified two unrelated females from the Des Moines area who had recently tested positive for Salmonella Blockley. Sporadically over the next two months, 21 more cases were reported.
METHODS: A case was defined as any patient with a Salmonella Blockley infection (isolated July 1 - September 18) that matched the pulsed-field gel electrophoresis (PFGE) pattern JBGX01.0001. Immediate in-depth interviews of cases were performed to determine potential exposures. PFGE analyses were performed on all S. Blockley isolates. The Iowa Department of Inspections and Appeals (DIA) performed multiple inspections of the implicated restaurant. All employees had stool testing performed, and 40 environmental (water, ice, food, and surface) samples were obtained at this restaurant and tested for Salmonella.
RESULTS: Twenty-three patients met the case definition. Interviews were performed on 21 cases (two cases were lost to follow-up). The median age was 35 years (range 5 – 76), and 52% (12/23) were male. Diarrhea was reported by 90% (19/21) of cases; two cases presented with urinary tract infections. Four cases (17%) were hospitalized. The implicated restaurant was visited by 71% (15/21) of cases in the seven days prior to illness onset. No other restaurant, chain, or other potential exposure entity was patronized by more than three cases. A common food exposure was not identified from patient interviews; this was expected due to the limited menu and common ingredients in most foods. All food and environmental samples were negative. All food handlers tested negative. Cases continued to occur after several routine interventions and correction of all identified food handling violations. Only after unique interventions did the outbreak stop.
CONCLUSIONS: The investigation implicated a specific restaurant, but no specific food item could be identified. Only with restaurant closure, destruction of all food in the restaurant, intensive cleaning of entire restaurant (air vents, all surfaces, outdoor freezer), and changing of all distributors (including an unlicensed distributor with multiple violations) did the outbreak end.