The virus
Noroviruses (genus Norovirus, family Caliciviridae), are a group of related RNA viruses that cause acute gastroenteritis in humans. Norovirus was recently approved as the official genus name for the group of viruses provisionally described as「Norwalk-like viruses」(NLV). It has been implicated as the most common etiological agent of non-bacterial gastroenteritis outbreaks. Noroviruses are relatively resistant and are able to survive freezing and temperature as high as 60oC.
Mode of Transmission
Noroviruses are transmitted primarily through the fecal-oral route, either by consumption of fecally contaminated food or water or by direct person-to-person spread. Environmental and fomite contamination may also act as a source of infection. Evidences also suggest transmission due to aerosolization of vomitus.
Incubation Period
The incubation period is usually 24 to 48 hours.
Clinical Features
The infection usually presents as acute onset of nausea, vomiting, abdominal cramps, and diarrhea. Vomiting is relatively more prevalent among children, whereas a greater proportion of adults experience diarrhea. Constitutional symptoms including headache, fever, chills, and myalgia are frequently reported. The disease is self-limited and the gastrointestinal symptoms usually last for 1 to 3 days with no long-term sequelae. Dehydration may occur in young children and elderly with chronic debilitating conditions. There is no long-term immunity and re-infection is possible.
Clinical Management
No specific antiviral therapy is available. Supportive treatment such as rehydration should be given especially in children and elderly.