Validity of Escherichia coli, enterovirus, and F-specific RNA bacteriophages as indicators of viral shellfish contamination

The sanitary classification of harvesting areas for bivalve mollusks in France is based on the level of Escherichia Coli contamination detected in shellfish meat, as defined in EC Directive 91/492 EEC. However, outbreaks of gastroenteritis or hepatitis after consumption of shellfish meeting current bacteriological standards suggest that E. coli is a poor indicator of viral contamination. The purpose of this study was to assess the adequacy of enterovirus and F-specific RNA bacteriophages as new indicators of human enteric viruses. Shellfish were sampled over a 37-mo period to characterize microbial contamination in two coastal areas subjected to different sewage contamination inputs. Contamination by E. coli, F-specific RNA bacteriophages (F+ RNA) and human enteric viruses (enterovirus, EV; hepatitis A virus, HAV; Norwalk-like virus, NLV: astrovirus, AV; and rotavirus, RV) was measured in the same samples. E. coli analysis was performed by conductance measurement, enteric viruses were detected by reverse-transcription polymerase chain reaction (RT-PCR) and hybridization. and F+ RNA was evaluated by culture according to the ISO 10705-1 method. Statistical analysis based on bootstrap methods was performed on 95 series of paired observations. The validity of E. coli, enterovirus, and F-specific RNA bacteriophages as viral indicators was evaluated by measuring their sensitivity and specificity in the presence of enteric viruses. None of the tested indicators proved adequate to protect the public from viral shellfish contamination. The sensitivity of all indicators was better in the highly contaminated zone, and enteroviruses showed the highest specificity for both sites.