The influence of the number of Escherichia coli results on the classification status and assessment of microbiological risk of shellfish production areas

Abstract

Classification of shellfish production areas (SPAs) based on monitoring for faecal indicator organisms is undertaken in many shellfish producing countries to assess the risk of contamination with pathogens and determine the level of post-harvest treatment prior to sale for human consumption. This study assessed the effect of the number of E. coli monitoring results on the classification status of SPAs using the A, B and C classification criteria prescribed in the European Food Hygiene Regulations. The assessment was based on a database of E. coli concentrations monitored in shellfish from seven production areas (>255 sample results/SPA) on the coast of Santa Catarina (Brazil). It was found that six SPAs would be classified as B and 1 as C if all the available results were considered. Ten series of 50 data samples were randomly extracted from each production area dataset (12–120 results/sample, in multiples of 12). Classifications given to each data sample resulted in two production areas that had been given B status based on the full database being classified more times as A than as B when data samples with 12 results were considered. There was a tendency for data samples compliant with class A to reduce with higher number of E. coli results/sample. The results indicate that areas with class B status can be misclassified as A during the initial classification when fewer results are available. Furthermore, areas with ‘prohibited’ status can be misclassified as C during the initial classification, when 12 results are considered in compliance assessments. Despite the preliminary nature of this study, the results underscore the need to consider long-term monitoring datasets in compliance assessments to ensure that the classification status of SPAs truly reflects environmental contamination levels.