A semiquantitative approach to estimate Norwalk-like virus contamination of oysters implicated in an outbreak

Gastroenteritis outbreaks linked to shellfish consumption are numerous and Norwalk-like viruses (NLVs) are frequently the responsible causative agents. However, molecular data linking shellfish and clinical samples are still rare despite the availability of diagnostic methods. In a recent outbreak we found the same NLV sequence in stool and shellfish samples (100% identity over 313 bp in the capsid region), supporting the epidemiological data implicating the shellfish as the source of infection. A semi quantitative approach using most-probable-number-RT-PCR (MPN-RT-PCR) demonstrated the presence of a hundred of RT-PCR units per oyster. Follow-up of the oysters in the harvest area, for approximately 2 months, showed persistence of NLV contamination of the shellfish at levels up to a thousand RT-PCR units per oyster prior to depuration of the shellfish. This finding is useful in beginning to understand shellfish contamination and depuration for use in future hazard analyses. (C) 2003 Elsevier Science B.V All rights reserved.