Genotype GI.6 Norovirus, United States, 2010–2012

Eyal Leshem

, Leslie Barclay, Mary Wikswo, Everardo Vega, Nicole Gregoricus, Umesh D. Parashar, Jan Vinjé, and Aron J. Hall

Author affiliations: Centers for Disease Control and Prevention, Atlanta, Georgia, USA

Abstract

We report an increase in the proportion of genotype GI.6 norovirus outbreaks in the United States from 1.4% in 2010 to 7.7% in 2012 (p< 0.001). Compared with non-GI.6 outbreaks, GI.6 outbreaks were characterized by summer seasonality, foodborne transmission, and non–health care settings.

Noroviruses are the leading cause of epidemic gastroenteritis, including foodborne outbreaks, and a major cause of sporadic gastroenteritis in the United States (1–3). Hospitalizations and deaths associated with norovirus infection occur most frequently among elderly persons, young children, and immunocompromised persons (2,4). Noroviruses can be divided into at least 5 genogroups (GI–GV) and at least 35 genotypes. Human disease is primarily caused by GI and GII noroviruses, and most norovirus outbreaks are caused by genotype GII.4 viruses (5). During the past decade, new GII.4 strains have emerged every 2–3 years, replacing previously predominant GII.4 strains (6–8). GI noroviruses are relatively uncommon, and systematic descriptions of GI outbreak epidemiology and characteristics are scarce (9). Before 2010, genotype GI.6 noroviruses were rarely reported in the United States; < 5 GI.6 outbreaks were reported each year to the Centers for Disease Control and Prevention (J. Vinjé, pers. comm.). We report the emergence of GI.6 norovirus as a cause of outbreaks in the United States and discuss its effect on public health.