Viral and Clostridium Perfringens Content of Hard Clams During Commercial Depuration

In order to assess the efficiency of enterovirus release by hard clams (Mercenaria mercenaria) during commercial deputation, pooled samples were analyzed for viruses and indicator bacteria (Clostridium perfringens) before and after depuration over a 28 month period. Bacterial content of undepurated clams varied seasonally, was consistent for a given location and date of harvest, but was unrelated to sanitary classification of overlying water based on fecal coliform content. The efficiency of Clostridium deputation varied widely, with no apparent seasonal pattern, although depuration efficiency correlated well with initial bacterial levels. Clostridium perfringens content was not a good indicator of viral content in Mercenaria mercenaria. Enteroviruses were recovered from clams on only 3 occasions, one of which was a single isolation from a pool of depurated clams. Because viral contamination of shellfish harvested from restricted water was not a common occurrence, laboratory simulations may provide the only practical means of evaluating viral deputation efficiency.