Evaluation of F-specific RNA bacteriophage as a candidate human enteric virus indicator for bivalve molluscan shellfish

Escherichia coli is a widely utilized indicator of the sanitary quality of bivalve molluscan shellfish sold for human consumption. However, it is now well documented that shellfish that meet the E. coil standards for human co nsumption may contain human enteric viruses that cause gastroenteritis and hepatitis. In this study we investigated using F-specific RNA bacteriophage (FRNA bacteriophage) to indicate the Likely presence of such viruses in sh ellfish sold for consumption. FRNA bacteriophage and E. coli levels were de termined over a 2-year period for oysters (Crassostrea gigas) harvested fro m four commercial sites chosen to represent various degrees of sewage pollu tion. Three sites were classified as category B sites under the relevant Eu ropean Community (EC) Directive (91/-492), which required purification (dep uration) of oysters from these sites before sale, One site was classified a s a category A site, and oysters from this site could be sold directly with out further processing. Samples were tested at the point of sale following commercial processing and packaging, AII of the shellfish complied with the mandatory EC E. coli standard (less than 230 per 100 g of shellfish flesh) and the levels of contamination for more than 90% of the shellfish were at or below the level of sensitivity of the assay (20 E. coil MPN per 100 g), which indicated good quality based on this criterion. In contrast, FRNA ba cteriophage were frequently detected at levels that exceeded 1,000 PFU per 100 g, High levels of FRNA bacteriophage contamination were strongly associ ated with harvest area fecal pollution and with shellfish-associated diseas e outbreaks. Interestingly, FRNA bacteriophage contamination exhibited a ma rked seasonal trend that was consistent with the trend of oyster-associated gastroenteritis in the United Kingdom. The correlation between FRNA bacter iophage contamination and health risk was investigated further by using a r everse transcription-PCR assay for Norwalk-like virus (NLV). NLV contaminat ion of oysters was detected only at the most polluted site and also exhibit ed a seasonal trend that was consistent with the trend of FRNA bacteriophag e contamination and with the incidence of disease. The results of this stud y suggest that FRNA bacteriophage could be used as viral indicators for mar ket-ready oysters.