The noroviruses are the leading cause of viral gastroenteritis worldwide and despite many studies showing victims remain ‘stool-positive’ for weeks after getting better the advice is still “48 or 72 hours symptom-free and you’re safe”.
In this latest study the Oregon Department of Public Health and the US Centers for Disease Control and Prevention analyzed 10 selected norovirus outbreaks from November 2009 through January 2013. Shedding of norovirus in stool occurred for at least 21 days and was significantly more likely if the initial stool sample had >1,000 copies of virus per gram.
For GII.4 viruses, the researchers found no association between secretor status or blood type and symptomatic infection (the noroviruses have 6 genogroups and 38 genotypes; strain GII.4 is most frequently associated with outbreaks (NEJM JW Infect Dis Mar 2013 and MMWR Morb Mortal Wkly Rep 2013; 62:55).