Comparison between Quantitative Real-Time Reverse Transcription PCR Results for Norovirus in Oysters and Self-Reported Gastroenteric Illness in Restaurant Customers

Norovirus is the principal agent of bivalve shellfish-associated gastroenteric illness worldwide. Numerous Studies using have demonstrated norovirus contamination in a significant proportion of both oyster and other bivalve shellfish production areas and ready-to-eat products. By comparison, the number of epidemiologically confirmed shellfish-associated outbreaks is relatively low. This study attempts to compare norovirus RNA detection in Pacific oysters (Crassostrea gigas) by quantitative real-time reverse transcription PCR (RT-PCR) and human health risk. Self-reported customer complaints of illness in a restaurant setting (screened for credible norovirus symptoms) were compared with presence and levels of norovirus as determined by real-time RT-PCR for the batch of oysters consumed. No illness was reported for batches consistently negative for norovirus by real-time RT-PCR. However. norovirus was detected in some batches for which no illness was reported. Overall presence or absence of norovirus showed a significant association with illness complaints. In addition, the batch with the highest norovirus RNA levels also resulted in the highest rate of reported illness. suggesting a linkage between virus RNA levels and health risks. This study suggests that detection of high levels of norovirus RNA ill oysters is indicative of significantly elevated health risk. However, illness Inlay not necessarily be reported after detection of norovirus RNA at low levels.