ABSTRACT
AIM: To investigate an increase in Salmonella typhimurium phage type 1 (STM1) cases identified in the Gisborne region (eastern North Island, New Zealand) in January 2009. METHODS: Initial investigations found that ham and watermelon were both consumed by a high proportion of cases. A case control study was conducted to determine if there was an association between cases of STM1 in Gisborne and consumption of ham or watermelon. Environmental investigations were conducted and included testing of ham and watermelon samples, as well as trace back of suppliers of these foods. RESULTS: The case control study included 15 cases and 40 controls and found that cases were seven times more likely to have eaten watermelon compared with controls (p=0.026). Cases were one and a half times more likely to have eaten ham compared with controls (p=0.620). Pulsed field gel electrophoresis analysis determined that cases were caused by indistinguishable STM1 isolates. Salmonella was not recovered from any food samples. Trace back found watermelons were purchased from roadside stalls and came from one grower. CONCLUSIONS: This outbreak was associated with watermelon consumption from a grower in the Gisborne region. The outbreak was most likely controlled by the implementation of chlorine washing of watermelons at the grower's pack house.
