A critical review of methods for detecting human noroviruses and predicting their infectivity.

Human noroviruses (hNoVs) are the single most common cause of acute non-bacterial gastroenteritis in the industrialized world but cannot be grown in simple culture systems. Different approaches for detecting hNoVs and predicting their infectivity are reviewed. Although reverse transcription quantitative PCR (RT-qPCR) is the most widely used method to detect human noroviruses (hNoVs) it is unable to discriminate between infectious and non-infectious particles. There is therefore a dilemma in assessing the risk to human health from samples detected as positive in RT-qPCR assays. In the absence of an efficient cell, culture based detection system for hNoVs RT-qPCR methods need to differentiate RT-qPCR signals from intact infective particles, intact defective particles, degraded particles (consisting of capsid protein and virus RNA, herein referred to as ribonucleoprotein complexes (RNPs), and "naked" RNA. This review provides a critical analysis of methods for detecting hNoVs, and differentiating such signals with reference to relevant studies of virus infectivity, structure, inactivation, and the disassembly of virus particles during infection. The application of these methods as an adjunct to the proposed RT-qPCR European Committee for Standards (CEN) methods for the detection of hNoVs in foods and the environment is discussed.