Surveillance of human norovirus in oysters collected from production area in Shandong Province, China during 2017-2018

Human norovirus (HuNoV) is the leading cause of non-bacterial gastroenteritis worldwide. Oysters are known food-related vehicles for HuNoV transmission. However, there are few data available on the viral contamination of shellfish from production areas in China. A one-year monitoring program was carried out to detect and characterize HuNoV contamination in oysters, collected from two shellfish commercial harvesting areas in Shandong province, China. Oysters were sampled every month from July 2017 to August 2018. From the 356 oyster samples, HuNoV was detected in 16.9% (60/356) using reverse transcription-qPCR. Of the 60 positive samples, 43.3% (26/60) were positive for HuNoV genogroup I (GI) only and 31.7% (19/60) were positive for genogroup II (GII) only. Both GI and GII were detected in 25.0% (15/60) samples. The majority (65.0%, 39/60) of positive samples were collected in winter months (November-December). There was no significant correlation between the detection of HuNoV in shellfish and the pH or fecal coliforms levels in seawater. Using next-generation sequencing, several HuNoV genotypes were identified including capsid genotypes GI.5, GI.6, GII.2, GII.3, GII.4_Sydney 2012, GII.13 and GII.14. These Results indicate that monitoring of HuNoV in oyster production area is necessary to ensure the safety of shellfish prior to distribution to consumers.

Automated summary

Human norovirus is the leading cause of non-bacterial gastroenteritis worldwide and oysters are known vehicles for its transmission. A year-long monitoring program in two shellfish harvesting areas in Shandong province, China, revealed 16.9% of oyster samples tested positive for HuNoV. The majority of positive samples were collected in winter months, with no significant correlation found between viral detection and seawater pH or fecal coliform levels.