An Outbreak Investigation of Cross-County Norovirus Gastroenteritis Linked to Imported Oysters, Taiwan, 2015

In August 2015, the Public Health Bureau of Changhua County received notification of a foodborne outbreak (outbreak A) associated with consumption of undercooked oysters. The norovirus genotype GI.5 was detected in the stool sample from one of the six consumers, and GI.1, GI.4, GI.5, and GII.17 were detected in oyster samples. The trace-back investigation of the oyster supply chain revealed that one foodborne outbreak occurred a week ago in Hsinchu County (outbreak B), in which the sequences of the norovirus GI.4 and GII.17 strains detected in stool samples were highly similar to those detected in oyster samples of outbreak A. The oyster batches found or suspected contaminated were subsequently recalled to halt the outbreak. The investigation benefited from excellent collaboration among public health departments of the mentioned counties and the successful traceability through the established food supply chain system. It also highlighted the importance of risk communication to the general public and catering sectors, regarding preparation of oysters and other shellfish which biologically tend to accumulate noroviruses.