Norovirus in retail shellfish.

Norovirus is a common cause of gastroenteritis outbreaks associated with consumption of raw shellfish. The majority of norovirus infections worldwide are due to genogroup II noroviruses. Bivalve molluscs (mussels, clams and oysters) at the end of the commercial chain, the points of purchase, were sampled between 2005 and 2008 in several retail points in Apulia, Italy, and screened by a semi-nested RT-PCR specific for genogroup II noroviruses. Noroviral RNA was detected in 12.1% of the samples, with lower frequency being observed in samples obtained from hypermarkets (8.1%) rather than in samples from open-air markets and fish shops (17.6% and 16.2%, respectively). By sequence analysis, the strains were characterized as norovirus variants GII.4/2004 and GII.b/Hilversum, which were both circulating in Italy in the same time-span.