The flu season has yet to wallop Vancouver this year but there's been a number of cases of Norwalk virus, public health officials say.

"Definitely Norwalk season has arrived," Vancouver Coastal Health medical health officer Dr. Reka Gustafson told CBC News on Thursday.

Outbreaks of severe gastro-intestinal illness, commonly called Norwalk or norovirus, have closed at least one day care and one elementary school in recent weeks.

Over the holiday season, Royal Columbia Hospital in New Westminster was closed to visitors after an outbreak of the virus infected several wards.

People often mistake Norwalk or similar inflections for "stomach flu," Gustafson said, but the symptomatic outbreaks of severe vomiting, diarrhea and weakness are not actually caused by influenza, but by bacteria or viruses like the Norwalk or rotavirus that hit the gastrointestinal system.

Regardless of whether it's viral or bacterial, these bugs can spread like wildfire and that's why it's important to remember how not to spread them, Gustafson said.

The best way to prevent the spread of Norwalk is to wash your hands frequently, especially after going to the bathroom. Those who have diarrhea should stay away from school, day care or work, and avoid food preparation until symptoms have subsided, said Gustafson.

People infected with norovirus are contagious from the moment they begin feeling ill until at least three or four days after recovery, according to Health Canada, and some people may be contagious for as long as two weeks after recovery.

According to Health Canada, there is no preventative treatment for noroviruses and they cannot be treated with antibiotics, which fight bacteria, not viruses.

As for influenza, the peak of the true flu season has yet to hit and there's still time for the very young, very old and those with weakened immune systems to get vaccinated, Gustafson said.

Influenza kills about 1,400 people in B.C. every year.