Occurrence of faecal bacteria, Salmonella and antigens associated with hepatitis A virus in shellfish

An investigation was carried out over a one year period to examine jointly the occurrence of faecal bacteria, salmonella and the presence of antigens associated with the hepatitis A virus (HAV) in oysters (Crassostrea gigas), mussels (Mytilus edulis, Mytilus galloprovincialis) and cockles (Cerastoderma edule), taken from 8 shellfish farming areas or natural beds along the French coast. For the faecal coliforms (FC) and faecal streptococci (FS), statistical analysis of the 176 samples examined shows a statistically significant difference between sampling stations (F = 44.39 and F = 26.69 respectively, p less than 0.001): 4 of the 8 stations are more highly contaminated. Salmonella and antigens associated with HAV were detected in 5% and 1.7% respectively of the samples analysed. Frequency of isolation of salmonella is higher for the group of sampling stations where the mean levels of contamination by FC and FS are highest. The presence of HAV associated antigens was detected for the group of stations showing the lowest mean contamination levels. Taking all sample stations together, the percentage of isolation of salmonella differs significantly (chi 2 = 7.28, p less than 0.01) for the two classes of FC established on the basis of the threshold value (300 FC). There is no difference between the two classes of FS. For the HAV-associated antigens, detection percentages are similar for the two classes of results for FC and FS. Within each sampling station, considered independently, no particular correlation was found between the various viral and bacterial markers investigated.