Differences in clinical presentation between norovirus genotypes in nursing homes

Background: In healthcare settings, norovirus (NoV) outbreaks are predominated by genotype II.4 (GII.4) strains. Periodically, new variants of GII.4 emerge, causing a temporary increase of outbreaks. Objectives: To study the relationship between symptoms and NoV genotype. Study design: Data of 49 nursing homes which were monitored for NoV outbreaks in the winter seasons of 2005/2006 and/or 2006/2007 were used. Results: Data on symptoms and duration of illness were available for 465 residents and 174 staff members from 28 NoV outbreaks. Genotype GII.4 was responsible for 21 outbreaks. Attack rates for residents seemed to be higher in GII.4 outbreaks compared to other genotypes. In outbreaks caused by GII.4, residents vomited more often than in outbreaks with other genotypes. They also had more often complaints of nausea, abdominal cramps, fever, and mucus in stool. The GII.4 2004 variant outbreaks showed higher percentages of nausea, stomach ache, and fever than outbreaks with the GII.4 2006a variant. Differences in duration of illness were not found. In nursing home staff, no clear differences were found between outbreaks caused by GII.4 and non-GII.4 NoVs. Conclusions: Genotype GII.4 was found to be related to more symptomatic disease, including more residents vomiting, and to a lesser extent, higher attack rates among residents. (C) 2009 Elsevier B. V. All rights reserved.