Monitoring of foodborne viruses in berries and considerations on the use of RT-PCR methods in surveillance

Foodborne viruses such as norovirus (NoV) and hepatitis A virus (HAV) are an important food safety concern and have been associated with many foodborne illness outbreaks linked to fresh and frozen berries worldwide. The standard method for qualitative detection of hepatitis A virus and norovirus from foods has been published in 2013 (ISO/TS 15216-2). Since then, multiple laboratories provide diagnostic methods, based on the ISO standard for foodborne virus detection from foods (including berries). In this study, surveillance data, collected by Nestlé and PROFEL (the European Association of Fruit and Vegetable Processors) for NoV and HAV on a wide range of (frozen) berries from 2009 to 2016 are reported. Seven positive signals were identified from 2,015 samples analyzed (0.3% [95%CI: 0.2-0.7%]). To assess the potential use of human adenovirus (HAdV) as “index viruses” of human fecal contamination for monitoring purposes, 632 berry samples, previously tested for NoV and HAV were also tested for HAdV. Six HAdV positives were recorded, corresponding to a prevalence of 0.9% (95%CI: 0.4-2.1%). None of the samples indicating presence of pathogenic viruses (NoV and HAV) were positive for HAdV. Analytical drawbacks and difficulties with results interpretation in berries during this monitoring program have been identified and are discussed. This study demonstrates that monitoring programs - even if providing numerous negative test results - are a useful means to provide baseline data, for a more comprehensive risk assessment related to foodborne viruses in berries.