Health officials warned Thursday that transmission of the nasty virus is picking up steam. They urged people to take precautions against catching and passing along the illness, including getting a flu shot.
"We are seeing a lot of influenza in the hospital. And anecdotally, a lot of people that I work with or people who work with them have been calling in sick in the last couple of weeks," said Dr. Michael Gardam, head of infection control at Toronto's University Health Network.
The season is off to its earliest start in several years and is a stark reminder of the unpredictability of the influenza virus.
Last year's flu season started so late — and was so mild, in relative terms — that for most of the season it seemed like the winter that flu forgot.
The timing of influenza's peak doesn't indicate how hard or moderate a flu season this might be. But with so much illness happening around the holidays, the opportunities for people to pick up a flu infection are pretty much ideal, experts say.
"We have long recognized that the holiday period is a chance for greater social mixing," said Dr. Danuta Skowronski, an influenza expert at the B.C. Centre for Disease Control in Vancouver.
"We sometimes refer to influenza as the original Grinch who stole Christmas because it can transmit more when there are people gathering in large numbers indoors."
Dr. John Spika of the Public Health Agency of Canada said that more than 25 per cent of tests for respiratory infections in Quebec are coming back positive for influenza at this point.
Ontario is seeing roughly the same amount of activity and the Prairie provinces are reporting that about 15 per cent of respiratory tests are positive for flu, said Spika, who is director general of the agency's centre for immunizations and respiratory infectious diseases.
Even the Atlantic provinces are getting into the action over the past week or so, he said. (Flu seasons in Canada typically start in British Columbia and work their way east.)
"Usually what we say is when they hit 10 per cent, we're into the flu season," Spika said to put the percentage figures into context.
Spika suggested activity in British Columbia may actually peaked, but Skowronski said the numbers she's seeing suggest the viruses are still going strong there.
"We're still seeing indications of climbing activity, and primarily due to H3N2 subtype viruses."
In fact, the influenza A virus H3N2 is the predominant strain circulating all across Canada at the moment, making up about 80 per cent of the viruses tested. H3N2 typically causes more severe illness, especially in seniors, Spika said.
He and others urged people who haven't had a flu shot yet to get one.
Even though it takes a couple of weeks for flu vaccine to build up a person's antibodies against the virus, there will be flu circulating for awhile still, Skowronski said.
"It takes a few weeks to mount a peak antibody response, but you do start developing antibody and it is increasing even within a week of being immunized," she said from Vancouver.
"And we don't know when this virus or its activity will peak. So it could be a couple of weeks from now."
People who are sick should try to keep their germs to themselves, Gardam said.
"If you are sick, stay away from people. So don't come into work, don't go to that Christmas party if you're really feeling ill, because that's just unfair to everybody else," he said.
He also advised people to wash their hands frequently.
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