Epidemiology of norovirus gastroenteritis in Germany 2001-2009: eight seasons of routine surveillance

We analysed data on laboratory or epidemiologically confirmed cases (n = 856,539) and on outbreaks (n = 31,644) notified during week 31 (2001) to week 30 (2009), and performed molecular typing of specimens from 665 outbreaks. We aimed at identifying demographic and molecular characteristics to inform on potential additional approaches to prevent disease spread in the population. The mean incidence by norovirus season (week 31 in one year to week 30 in the following year) was 130 (range 19-300) cases/100,000 population and was highest in persons aged <5 years (430/100,000) and ≥ 75 years (593/100,000). The proportion hospitalized in community-acquired cases was 8-19% per season. The mean norovirus-associated mortality was 0.05/100,000 per season and 0.5/100,000 in the ≥ 75 years age group. Most outbreaks with known setting (75%) occurred in hospitals (32%), nursing homes (28%), households (24%) and childcare facilities (10%). GII strains dominated in the outbreak specimens. GII.4 strains were found in 82% of nursing home outbreaks, 85% of hospital outbreaks, and 33% of childcare facility and school outbreaks. Cases in younger individuals were notified earlier during the season than adult cases, and outbreaks in childcare facilities and schools preceded those in nursing/residential homes, hospitals and private households. We suggest future studies to investigate more closely potential transmission patterns between children and adults.