In developed countries, most cases of gastroenteritis are caused by viral infection. Viral etiologies of gastroenteritis include human caliciviruses (including noroviruses and sapoviruses), astroviruses, enteric adenoviruses, and rotaviruses (table 1). Norovirus is the most common cause of gastroenteritis in adults and children. Norovirus causes 19 to 21 million illnesses, including 570 to 800 deaths, 56,000 to 71,000 hospitalizations, 400,000 emergency department visits, and 1.7 to 1.9 million outpatient visits .
The clinical manifestations and diagnosis of norovirus and related viruses will be reviewed here. The epidemiology and management of acute viral gastroenteritis in adults are discussed separately. (See "Epidemiology and pathogenesis of viral gastroenteritis in adults" and "Acute viral gastroenteritis in adults".)
Issues related to rotavirus are discussed separately. (See "Clinical manifestations and diagnosis of rotavirus infection" and "Rotavirus vaccines for infants".)
Norovirus and sapovirus — The human caliciviruses that cause acute gastroenteritis have a worldwide distribution and are divided into two genera, the noroviruses and the sapoviruses. Noroviruses were first identified as viral causes of gastroenteritis in an outbreak in Norwalk, Ohio, and were previously referred to as the Norwalk-like viruses. Sapoviruses were first identified as viral causes of gastroenteritis in Japan and were previously referred to as the Sapporo agent.
Caliciviruses contain a single-stranded RNA genome and have a relatively simple structure, containing one major (VP1) and one minor (VP2) capsid protein . Expression of the VP1 in experimental systems leads to formation of empty capsids or virus-like particles (VLPs) that are useful tools to generate immune reagents and investigate pathogenesis. Caliciviruses are also capable of recombining with viruses in other families, producing novel viruses of uncertain importance in human disease [3,4].