Molecular Epidemiology of Norovirus in Outbreaks of Gastroenteritis in Southwest Germany from 2001 to 2004

The identification and molecular epidemiology of norovirus in outbreaks of gastroenteritis were studied during a 3-year period in Germany. Specimens (n = 316) from 159 nonbacterial gastroenteritis outbreaks from March 2001 to June 2004 were analyzed for the presence of noroviruses by reverse transcriptase PCR. Outbreaks were most frequent in elderly people's homes and care centers (43%), followed by hospitals (24%). Molecular analyses of strains from 148 outbreaks showed that there were up to 12 genotypes involved in the outbreaks. Genogroup II noroviruses were responsible for 95% of the outbreaks. Cocirculation of more than one strain in the same outbreak and cocirculation of genogroup I and II strains in the same place were observed. Genogroup II4 (Grimsby-like) was the most prevalent strain, accounting for 48% and 67% of the outbreaks in 2002 and 2003, respectively. The genogroup IIb (Castell/Suria) genotype was observed in all the years of the study. Epidemiological and molecular data indicated that there was a major shift of the predominant strain that coincided with the appearance of a new variant of genogroup II4 in 2002. By the application of reverse transcriptase PCR, this study has demonstrated the importance and dynamism of noroviruses in Germany.