Publication Abstract

Spatial and temporal pattern of norovirus contamination in a Pacific oyster fishery

Spatial and temporal pattern of norovirus contamination in a Pacific oyster fishery

A Cook, J Lowther, M Price-Hayward, R Lee

An outbreak of viral gastroenteritis occurred in the UK during the summer of 2007. The suspected cause was norovirus contaminated Pacific oysters (Crassostrea gigas) from an aquaculture site. The farm in question consisted of a large number of oyster trestles stretching approximately 1.3 km along the shore, with most potential sources of viral contamination (septic tank outfalls) located at one end. Monthly sampling of oysters was undertaken over the course of a year at four separate locations evenly spread along the fishery. Samples were tested for norovirus genogroups I and II using a semi-quantitative real-time reverse transcription PCR technique, with results reported in PCR units. In addition to the samples collected for norovirus analysis, oyster samples were taken for E. coli analysis on most occasions.  On every sampling occasion over the 12 month period at least one sample tested positive for at least one norovirus genogroup. The levels and prevalence of contamination for genogroup I were lower than for genogroup II, and any spatial or temporal trends in contamination levels were less apparent for genogroup I. Total levels of norovirus never exceeded the levels reported from the batch of oysters suspected of causing the outbreak. For both genogroups a significant seasonal effect was found, with mean results highest during the first quarter of the year. No spatial pattern was apparent for genogroup I. A statistically significant spatial pattern in contamination levels was found for Genogroup II, with mean results decreasing with distance from the suspected contamination sources, implying that currents were carrying the contamination from these sources along the fishery. Comparison between levels of E. coli and norovirus genogroups I and II in paired oyster samples did not show a significant relationship.

Reference

A Cook, J Lowther, M Price-Hayward, R Lee (2009) Spatial and temporal pattern of norovirus contamination in a Pacific oyster fishery.In the Proceedings of the Seventh International Conference on Molluscan Shellfish Safety, Nantes, France (P. Lassus, ed), IFREMER, pp:81-87

A Cook*, J Lowther*, M Price-Hayward*, R Lee*

In the Proceedings of the Seventh International Conference on Molluscan Shellfish Safety, Nantes, France (P. Lassus, ed), IFREMER, pp:81-87