Norovirus outbreaks in long-term care facilities. Catalonia, 2017-2018

Abstract

Norovirus is the leading cause of outbreaks of acute viral gastroenteritis. We carried out this study to investigate outbreaks in long-term care facilities reported in 2017 and 2018 in Catalonia (Spain). The characteristics of the centres, exposed persons and the genogroups responsible were analyzed. Viral loads were estimated. The attack rate (AR), rate ratios (RR) or the odds ratio (OR) and its 95% confidence intervals were calculated. The mean cycle thresholds (Cq) were compared using the t-test for independent means. We included 30 outbreaks (4,631 exposed people). The global AR was 25.9%. The RR of residents vs. staff was 2.28 (95%CI 2.0-2.6). In residents with total or severe dependence the attack rate was 85.16% and in residents with moderate and low dependence or independent was 69.13% (RR 1.23, 95% CI 1.05–1.45). ARs were higher in smaller centres than in larger ones (34.4% vs 19.5%; RR 1.76 (95%CI 1.60–1.94). GII was responsible for 70% of outbreaks and 78.5% of identifications. No association was found between the genogroup and presenting symptoms (OR 0.96; 95% CI 0.41 to 2.26). Viral loads were higher in symptomatic than in asymptomatic patients (p = 0.001). Because norovirus was detected in asymptomatic persons, control measures should be applied not only to people with symptoms but to all persons in LTCF where norovirus outbreaks occur.