An epidemic of the Norwalk virus that brought Toronto's health-care system to the verge of collapse is finally winding down.

"I think the worst is over," said Donald Low, chief of microbiology for Toronto's University Health Network yesterday.

There are still 11 health-care facilities in Toronto, including nursing homes and two wards at Toronto East General Hospital, that remain closed because of an outbreak of the stomach virus, Dr. Low said. For the next four days, family and friends of people in the in-patient units at East General will only be allowed to contact them by phone.

But restrictions have been lifted at several other hospitals. Last week, the number of restricted wards was 25 throughout the city. Two weeks ago, at the peak of the epidemic, the count was 50, including six emergency rooms.

The hospitals' closing of emergency facilities and surgeries was not just a precaution, Dr. Low said.

As many as 30 per cent of the doctors and nurses in hospitals with outbreaks had to book off because they got sick with the infection that causes vomiting, diarrhea and nausea.

Fortunately, none of the hundreds of cases reported became life-threatening. "When you have it, it just feels like the killer plague," said Dr. Low. But unless someone is already very ill with another disease, the infection passes through the body within two to three days.

The virus family that causes the illness is not new. Before it got the name during an outbreak in Norwalk, Ohio, the illness had many names including winter vomiting, mountain flu or simply stomach flu. It has always been most common around the Christmas season, but it can strike in clusters of infection at any time of the year, Dr. Low said.

The risk remains high as people gather for Christmas parties because large numbers of people are together in enclosed spaces.

While the virus usually gets from person to person in water or food that has been touched by someone who is infected, Dr. Low has found evidence it can also be passed through the air.

When someone throws up, as many as 30 million copies of the virus could end up being spread through a room.

Dr. Low believes the low humidity in heated indoor air allows the round viruses to carry so that they can be breathed in. The virus can also survive on surfaces and get into the body by rubbing eyes or touching the mouth.

But the main precautions remain the same. Avoid seafood, which can concentrate the virus from water that has only a trace of the virus in it. Be cautious of raw food that has been handled by others at a party. Washing hands is always a good idea, but advice to use antibiotic soap won't help much, because the disease is spread by virus and not bacteria.