Noroviruses, the leading cause of severe gastroenteritis worldwide, 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).

Histo-blood group antigens (HBGAs) may act as attachment factors for norovirus: People with a functional FUT2 gene (secretors) express HBGAs on mucosal epithelium; nonsecretors, who have a FUT2 mutation of guanine-to-adenine at codon 428, are presumed to be protected from norovirus infection.

The Oregon Department of Public Health and the U.S. Centers for Disease Control and Prevention have analyzed 10 selected norovirus outbreaks (9 related to strain GII.4) from November 2009 through January 2013. They studied 62 cases, 34 exposed controls, and 18 nonexposed controls. Illness duration was significantly longer in people age 70 or older than in younger patients. Norovirus was detected in stool in 42 cases (68%). Shedding of norovirus in stool, which occurred for at least 21 days in 16 of 35 cases (47%), was significantly more likely if the initial stool sample had >1010 copies of virus per gram than if it had fewer copies per gram. For GII.4 viruses, the researchers found no association between secretor status or blood type and symptomatic infection.

Prolonged shedding of Norovirus after infection

Neil M. Ampel, MD reviewing Costantini VP et al. Clin Infect Dis 2016 Jan 1.

http://www.jwatch.org/na40028/2016/01/05/prolonged-shedding-norovirus-after-infection