Methods for detection of viruses in food (Norovirusand hepatitis A virus)

Abstract

The importance of hepatitis A virus (HAV) and especially Norovirus (NoV) as causes of foodborne disease has mainly been established through diagnostics on patient samples combined with epidemiological studies. To improve understanding of transmission routes and to be able to implement preventive measures, efficient tools for virus detection in foods are needed. During the past decade, efforts have been made to develop these tools and a European standard for foods most often involved in virus transmission - such as fresh produce and bivalve molluscs - has been established, although there are still shortcomings. As a high sensitivity is needed, virus detection in foods is in general based on molecular methods like reverse transcription polymerase chain reaction (RT-PCR). Prior to detection, the viruses must be extracted and concentrated from the food matrix. These processing steps result in loss of virus and thereby low recovery. A wide range of foods may transmit viruses and, ideally, optimised methods for processing should be established for each type. For reasons of simplicity, basic principles of processing are used and adjusted to the specific type of matrix. After having described the various foods at risk as evidenced by data obtained using current methodologies in studies of outbreak and field screening, this chapter provides procedure steps (including alternatives) that are necessary for the detection of NoV and HAV. This includes processing of matrix, extraction/purification of RNA and detection by RT-PCR. Also, sampling and interpretation of positive results are discussed, as the lack in sampling plans and infectivity tests for HAV and NoV is problematic. Characterisation and quantification of viral RNA is covered, including a description of quality controls that are crucial to provide reliable results. Establishment and use of standardised methods will hopefully ease the collection and interpretation of data, so that their significance for human health can be understood.