**1. Introduction**

Enteric viruses have been increasingly recognized as the leading causative pathogens in foodborne disease outbreak, causing 66.6% of foodborne illnesses in the United States, compared with 14.2% and 9.7% for *campylobacter* and *salmonella*, respectively [1]. A multitude of foodborne viral pathogens include (but are not limited to) human noroviruses (hNoVs), rotavirus, hepatitis A virus (HAV), hepatitis E virus, astrovirus, aichivirus, sapovirus, parvovirus, enterovirus, and adenovirus [2]. Foodborne viruses are transmitted not only through contaminated food and water, but also in combination with close contact with infected individuals, aerosol contamination of projectile vomit, or through contamination of environ‐ mental surfaces. Potentially fecal-contaminated food, such as bivalve molluscan shellfish harvested in polluted water areas, fresh produce irrigated with contaminated water or harvested by an infected worker, and ready-to-eat foods prepared by an infected food handler

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are a means of infection [3—5]. Of all the foodborne viruses, hNoVs and HAV are the most important foodborne viral pathogens with regard to the severity of the associated illnesses and frequent occurrence worldwide [2]. Both hNoVs and HAV display high environmental stability on contaminated objects, are abundantly excreted in human feces (e.g., exceeding 107 viral particles per gram of stool), and have a low infectious dose (1 to 100 infectious viral particles) [2], all of which contribute to the ease of transmission of the viruses within a community. It is commonly noted that one of the most efficient ways to prevent and control the foodborne viral infections is to implement a reliable surveillance system using rapid, sensitive, and precise diagnostics to identify the associated pathogens. Human NoVs do not replicate in cell culture. Wild-type HAV strains are not readily cultivated *in vitro* and the detection is impaired by their slow and inefficient growth in cell culture and lack of apparent cytopathic effect. Cell culture-based systems for determining virus infectivity are currently not available for hNoVs and wild-type HAV. Traditional diagnosis of these foodborne viral pathogens has been reliant on electron microscopy and immunological tests, but these methods lack sufficient sensitivity. While they may be useful for the detection of the viruses in clinical specimens that contain high amounts of viruses, for foods, which harbor potentially small quantities of viruses and may yet cause illness, it is not feasible to use these traditional laboratory methods to detect the viruses. This has led to the development of new, more sensitive and robust detection methods. In recent years, the majority of newly developed detection approaches are nucleic acid-oriented. Nucleic acid-based molecular methods have demonstrated a large improvement in speed, sensitivity, and accuracy of the detection of hNoV and HAV, bringing new insights into the etiology and diagnosis of foodborne viral disease. This chapter will touch upon a number of nucleic acid-based methods that have been devel‐ oped and applied to detect the two epidemiologically important foodborne viruses.
