A Systematic Review of Human Norovirus Survival Reveals a Greater Persistence of Human Norovirus RT-qPCR Signals Compared to Those of Cultivable Surrogate Viruses

Human noroviruses (hNoV) are the single largest cause of acute gastroenteritis in the western world. The efficacy of hNoV control measures remains largely unknown, partly owing to the inability to grow the virus in vitro and partly to the large number of surrogate studies of unknown relevance. A systematic review of the persistence and survival of hNoV in foods and the environment was undertaken based upon PRISMA (preferred reporting items for systematic reviews and meta analyses) guidelines to answer the questions: (1) "What are the natural hNoV persistence characteristics in food and the environment?" and (2) "How can these properties be altered by applying physical and/or chemical treatments to foods or food contact surfaces?" Over 10,000 citations were screened using defined inclusion and exclusion criteria. One hundred and twenty-six (126) citations were identified for further evaluation and data were extracted based upon the conditions of study and treatment (e.g., treatment parameters, pH, and temperature, time, infectivity, and RT-qPCR results). Since the only markers for hNoV persistence and survival were RT-qPCR data and human challenge studies, citations for further analysis were restricted to only those that included data on hNoV behavior (using RT-qPCR) as compared directly to surrogate virus behavior (using both RT-qPCR and infectivity) in the same study, and clinical studies. Based on these criteria, a total of 12 independent studies (5 for thermal inactivation and 7 for available chlorine) and 3 human challenge studies were identified. RT-qPCR always underestimated reductions in surrogate virus titre as a function of treatment when compared to infectivity. The corresponding reductions in RT-qPCR signals for hNoV under comparable conditions were nearly always less than those observed for the surrogates. These relationships were statistically significant for heat when comparing persistence of hNoV RT-qPCR signals with surrogate MNV-1 RT-qPCR signals (P equal persistence=<0.07); and for free chlorine when comparing persistence of hNoV RT-qPCR signals to those of FCV F-9 (p=<0.01). Overall the data suggest that hNoV are frequently more resistant to typical food and environmental control measures compared with cultivable surrogate viruses, when basing data on comparative RT-qPCR results.