by Raymond Chow

Norwalk and Noroviruses - General Overview  

Norwalk virus was first identified as the cause of a primary school outbreak of vomiting/diarrhea in Norwalk, Ohio in the early 1970’s. Since that outbreak, similar viruses have been identified as the cause of outbreaks in Montgomery County, Hawaii, Snow Mountain, Taunton, Toronto, and during the Desert Storm campaign. Like Norwalk virus, these viruses have been named after their geographic setting and share similar symptoms and epidemiology. This group of viruses is collectively referred to as Noroviruses. Noroviruses cause viral gastroenteritis predominately during the winter in temperate climates.

Norovirus outbreaks may be the result of poorly controlled water management, contamination of food (particularly during preparation for large numbers of people), and/or amplification of person to person spread. Institutional outbreaks in hospitals, daycare facilities, nursing homes, schools, and hostels are common. On average, there are 40 institutional outbreaks in Toronto every year.

The Noroviruses has an incubation period of 12 to 48 hours. Illness is characterized by the sudden onset of vomiting and/or diarrhea. Other symptoms commonly reported are nausea, abdominal cramps, fever, headache, chills and muscle aches. Symptoms usually last 1 to 3 days, while 2-3% of cases experience symptoms for longer.