A quantitative method for estimating the likely intake of norovirus copies through consumption of Irish oysters

More than 50% of oyster-linked microbial illness is caused by Norovirus, adding a significant fraction to the overall burden of foodborne illness. The past decade has seen robust molecular methods developed to detect and... [ view full abstract ]

More than 50% of oyster-linked microbial illness is caused by Norovirus, adding a significant fraction to the overall burden of foodborne illness. The past decade has seen robust molecular methods developed to detect and quantify norovirus contamination in commercial oysters. However, there is limited information available to help translate these detected contamination levels into quantifiable risk estimates. The objective of this work is to establish a quantitative estimate of the likely number of virus copies ingested through consumption of Irish oysters.

The study builds on previous work that examined the distribution of GII.4 concentrations in individual C. gigas oysters. This distribution is now modelled using a log-normal distribution, whose parameters can be wholly determined by a single site concentration estimate. Combining this model of concentration with a model of oyster size gives a new log-normal model that estimates total virus copies per oyster consumed.

The method presented takes this new distribution of copies per oyster, and considers a single consumption event of 1-5 oysters. It returns a new distribution describing the expected number of copies consumed, which can be used for evaluating and managing risk.

The accuracy of this final consumption distribution was assessed by taking oyster samples with known concentration levels and using non-parametric bootstrapping to simulate thousands of possible consumption events from them. The simulated meals were shown to follow the predicted distribution.