Hyperemesis hiemis--a sick hazard.

Epidemic non-bacterial gastroenteritis or winter vomiting disease is a well recognized clinical syndrome causing significant morbidity in the general population and in semi-closed communities. The Norwalk group of viruses has become established as the aetiological agents responsible for this important clinical syndrome. As a result of their historically poorly-defined taxonomic status they have been alternatively described as small round structured viruses (SRSVs) which allow their differentiation from other morphologically distinct small round viruses, e.g. astroviruses, and classical human enteric caliciviruses. The Norwalk viruses are highly infectious, give rise to high secondary attack rates through person-to-person transmission and are common causes of outbreaks in hospitals leading to either ward or hospital closures. Transmission occurs via the faecal/oral route but also, and probably more importantly, from projectile vomiters, through environmental contamination. Inhalation of aerosolized virus arising from projectile vomiters is a possibility which requires further study. Laboratory diagnosis is currently achieved by electron microscopy but the recent molecular characterization of this group of viruses will allow the development of sensitive and specific assays. The future control of hospital outbreaks will rely heavily on effective control of infection procedures.