During a 2-year survey in an academic hospital, 8 (8.4%) of all norovirus (NoV)-positive patients showed prolonged norovirus illness and shedding (duration, 21-182 days). All patients had underlying illnesses, resulting in some level of immunodeficiency in 5. Four patients were admitted to the hospital with gastroenteritis, 2 acquired norovirus while hospitalized, and 2 were outpatients. Genotypes GII.4 and GIIb-GII.3 were found. Reinfection occurred in 3 patients. Full capsid sequences were determined from strains detected in sequentially collected stool specimens to study evolution. The greatest number of amino acid mutations in a given patient was 11; they were detected in NoV isolates recovered over a 119-day period and were mapped to positions at or near putative antigenic sites. In the patient with most severe immune dysfunction, only 5 amino acids mutated over 182 days, suggesting immune-driven selection. The severe impact on patients and hospitals and the potential role of prolonged shedders as a reservoir for viral antigenic variants lead us to stress the importance of confinement of outbreaks of NoV infection that occur in hospitals.

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Persistent URL dx.doi.org/10.1086/591627, hdl.handle.net/1765/29106
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Siebenga, J.J, Beersma, M.F.C, Vennema, H, van Biezen, P, Hartwig, N.G, & Koopmans, M.P.G, D.V.M.. (2008). High prevalence of prolonged norovirus shedding and illness among hospitalized patients: A model for in vivo molecular evolution. The Journal of Infectious Diseases, 198(7), 994–1001. doi:10.1086/591627