H3N2 flu is surging — and just had the ‘perfect environment’ for a spike

The H3N2 flu strain is landing more people in the hospital in the United States, and experts are urging Canadians to exercise caution amid a “perfect environment” for spread and a fresh round of case numbers expected in this country next week.

The U.S. Centers for Disease Control and Prevention (CDC) estimates that 7.5 million Americans have been infected and 81,000 have landed in the hospital this flu season, the health agency said on Thursday.

1:48 3 kids die from influenza A-related complications since start of December in Ontario

“Some parts of the United States are reporting the highest rates of flu hospitalizations since they’ve kept records,” said Dr. Fahad Razak, internal medicine physician at St. Michael’s Hospital and professor at the University of Toronto.

In the week ending Dec. 20, one in four (25.6 per cent) cases of every influenza test conducted in the U.S. came back positive, the CDC said.

This was a sharp increase from 15.7 per cent of tests coming back positive in the week ending Dec. 13 and nine per cent for the week ending Dec. 6.

For the week ending Dec. 20, 19,053 people were admitted to hospital in the U.S. with the flu. Five children died in the U.S. in the week ending Dec. 20 after an association with influenza, the CDC added.

The dominant strain in the U.S. and Canada this year is a strain called H3N2 subclade K.

Get weekly health news

Receive the latest medical news and health information delivered to you every Sunday.

Sign up for weekly health newsletter Sign Up

By providing your email address, you have read and agree to Global News' Terms and Conditions and Privacy Policy.

Canadians should be cautious in the weeks coming out of the holidays, Razak said.

“We have data that is very suggestive that we’re having an incredibly bad flu season here in Canada as well,” he said.

4:04 Ask the Expert: Protecting yourself and your family against the flu

“We can look to other countries, the experience in parts of Europe, now the United States and before that in Australia and Japan suggested some of the worst, or the worst, flu seasons on record,” he added.

Razak said the “enormous amount of human flow between the two countries, especially over the holidays,” should give Canadians pause.

“That is a perfect environment for an infectious disease to spread,” he said as Canadians and Americans return from seeing family on both sides of the border over the holiday season.

“If you think about our border with the United States, it’s the kind of border where when you have a high rate of illness that’s transmissible on one side, it’s nearly impossible to keep it out from the other side,” he added.

The rate of hospitalization from influenza in Canada has nearly doubled compared to the previous week of available data, with infections now up almost 30 per cent, Health Canada’s latest figures show.

For the week ending Dec. 13, Canada saw 11,646 new cases of flu being detected, which means 27.7 per cent of all the tests conducted in the country came out positive.

Health Canada’s next flu update, which will include data from the period covering Christmas Day, will be released next week.

1:50 Flu vaccine uptake declining nationwide

“More people in general are getting sick, so the volume of infections is higher. And when you have more people infected, there’s more people who can get critically unwell and end up in hospital,” he added.

As children get ready to head back to school on Monday after the holiday season, Razak said there is still time to get yourself and your family vaccinated.

“If your child has not been vaccinated, please get vaccinated. There’s never a better time than today,” he said.