Failure to detect norovirus in a large group of asymptomatic individuals.

Noroviruses are a major cause of both sporadic and epidemic gastroenteritis in humans, but the mechanisms by which norovirus circulates within the community are poorly understood. In this study, we examined the hypothesis that asymptomatic people act as a reservoir for norovirus. Faecal specimens from 399 asymptomatic individuals were tested for norovirus by reverse transcription polymerase chain reaction (RT-PCR) methodology, and no norovirus was detected. The failure to detect norovirus was not apparently due to the test sample being resistant to norovirus infection, nor to the presence of PCR inhibitors in the test sample. The findings suggest that, if norovirus is carried by asymptomatic people, the carriage rate is very low; the upper bound (95% confidence interval, binomial distribution) of the carriage rate was only 0.8%. Thus, it is unlikely that asymptomatic people are an important reservoir for norovirus.