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Acute gastroenteritis outbreaks in Catalonia, Spain: Norovirus versus Salmonella

Objective. To describe the epidemiology of norovirus (NV) and Salmonella gastroenteritis outbreaks in Catalonia between 15 October 2004 and 30 October 2005. Material and methods. Epidemiological data were obtained from outbreak reports. The aetiologic agent was investigated by culture for enteric bacteria, enzyme immunoanalyses, reverse transcription polymerase chain reaction (RT-PCR) and molecular epidemiology genotyping for NV. The χ2 test was used to compare proportions. Incidence rates and their confidence intervals (CI) were calculated assuming a Poisson distribution. Results. A total of 225 acute gastroenteritis (AG) outbreaks were reported, with 3436 persons affected and 115 hospitalized. Sixty outbreaks (27%) accounting for 1791 cases (52%) were caused by NV, with an attack rate (AR) of 34.7% and a hospitalization rate (HR) of 0.2%. Seventy- four outbreaks (33%) were caused by Salmonella spp., affecting 646 persons (18.8% (AR 45.6% and HR 13.7%)). The difference in AR between Salmonella spp. and NV was statistically significant (odds ratio (OR) 1.57; 95% CI: 1.39–1.78; p <0.001). The median number of affected persons per outbreak was 3-fold higher for NV (15 (2–174)) than for Salmonella (5 (2–44)). The incidence rate of AG cases associated with NV outbreaks was significantly higher (24.9 per 100,000 persons/year (95% CI: 23.7–26.1)) than for those associated with Salmonella (5(2–44)) outbreaks (9.2 per 100,000 persons/year (95% CI: 8.5–9.9)). Conclusions. The disease burden and impact of NV highlight the importance of timely notification and investigation of outbreaks and the development and implementation of preventive measures, such as health and safety education for caregivers and food handlers in order to reduce the incidence of infections.