A new strain of the highly contagious norovirus has put several British Columbia health-care facilities on the alert as the province deals with the highest rates of infection it has seen in years.

Natalie Prystajecky, a research scientist for the Provincial Health Services Authority's Microbiology and Reference Laboratory, said the PHSA has already observed more incidents of norovirus in B.C. in November and December than it has since 2006. It is a pattern that echoes reports from around the world.

"It does seem this is a high year for most jurisdictions," she said, citing the particularly high rates of norovirus in Britain as an example. According to that country's independent Health Protection Agency, the number of confirmed cases this season is already 83-per-cent higher than over the same period last year.

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Norovirus – sometimes referred to colloquially as the "winter vomiting bug" and incorrectly as the "stomach flu" – is characterized by the sudden onset of nausea, vomiting and diarrhea, typically followed by chills and muscle aches. Infected persons usually recover in one or two days, but the virus can be more serious to young children, the elderly and people with other health conditions.

It is spread through direct contact with an infected person or by eating food, drinking beverages or touching surfaces contaminated with the virus.

While norovirus is fairly common each winter, a new strain means more people will be infected, as immunity to one strain does not protect against infection with another strain. In comparison, a person is presumed to be immune to measles after having been infected with it once.

"We know we're in for a bad year because it's a different strain and every time there's a different strain we get more cases," said Paul Van Binder, chief medical health officer at New Westminster's Royal Columbian Hospital, where 12 patients and six staff members have fallen ill with the virus since Friday.

Staff at the RCH closed an entire floor – comprising the hospital's acute care for the elderly (ACE) unit and a general medicine unit – as a precautionary measure and introduced "aggressive supercleaning" to combat the bug, Dr. Binder said. The ACE unit is expected to reopen Thursday and the general medicine unit on Friday.

A new strain of norovirus typically appears every three to four years.

At Greenwoods Eldercare Society on Salt Spring Island, 21 residents and 25 staff members were infected since Dec. 21, complex-care co-ordinator Ryan Gibson said. Staff closed the 51-bed facility on Dec. 24 and mandated staff members displaying symptoms to stay home. Remaining staff members – who wore protective gowns, masks and booties – worked overtime over the holidays and were told not to travel between the society's two facilities. Residents were asked to remain in their private rooms.

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"We did cancel all of our activity programs and we had lots of activities planned for Christmas and New Year's," Mr. Gibson said. "When we needed the assistance the most, we were actually sending people away. It was tough."

At Vancouver General Hospital, one ward in the Centennial Pavilion and the second floor of the Banfield Pavilion, a residential care facility on the VGH campus, have gone under "containment protocol," said Vancouver Coastal Health spokeswoman Anna Marie D'Angelo. Patients with similar symptoms have been grouped together to prevent the spread of the virus.

But while the virus is very infectious and its effects highly unpleasant, doctors stress it is a relatively mild disease.

"This is not something to be alarmed about," Ms. Prystajecky said. "Norovirus continues to evolve and we see the emergence of new strains. Typically, norovirus is not that serious. Not that I'm trying to diminish it, but it is a self-limiting illness and most people will recover within 24 or 48 hours.

The best offence, Ms. Prystajecky said, is good hygiene: Frequent and prolonged hand washing, along with frequent cleaning of environmental surfaces with a bleach solution, can help minimize the risk. Those who display symptoms should remain at home, stay hydrated and avoid contact with particularly vulnerable populations such as children and the elderly if possible.

There is no vaccine or treatment for norovirus infection.