The European Commission requested scientific technical assistance in the preparation of a survey protocol for a European Union (EU) coordinated monitoring programme on the prevalence of norovirus (NoV) in raw oysters. The objective of the survey is to estimate the European prevalence of norovirus-contaminated oysters at production areas and batches of oysters at dispatch centres, with a 95% level of confidence and a level of precision of 5% considering an expected prevalence of 50%. The survey protocol defines the target population, the sample size for the survey, sample collection requirements, the analytical method for the quantification of NoV copy number (genotype I and genotype II), the data reporting requirements and the plan of analysis. The sample unit in production areas is a classified production area actively growing commercial oysters (whether harvesting or not is occurring) and for dispatch centres is a quantity of live oysters which are being packed and labelled with an Identification Mark. Based on a multistage sampling scheme, 1,026 samples from 171 production areas and 1,182 samples from 197 dispatch centres should be taken annually in Europe. To reduce the probability of surveying an atypical year, the survey is to be repeated for a second year. The samples are to be analysed according to the method specification developed by the European Union Reference Laboratory (EURL) expert working group, which is compliant with ISO/DIS 15216-1. Generalised linear models will be used to estimate proportion (with 95% confidence intervals) of sample units with NoV contamination for the following thresholds: < limit of quantification (LOQ), 100, 200, 500, 1,000, 5,000, 10,000 and > 10,000 copies/g. The necessary data to be reported by the sampler and the laboratory to support this analysis is presented in two data models. The results of the survey should be reported using the EFSA data collection framework.
