TORONTO – The number of flu cases is continuing to spike across Canada, suggesting the peak of the season could still be a few weeks off, say infectious diseases experts, who describe this influenza season as “unusual.”
“We really haven’t seen a season quite like this in a little while,” said Dr. Michelle Murti of Public Health Ontario, referring to the mix of two strains dominating this year’s flu epidemic.
The dominant influenza A strain is H3N2, a nasty virus that tends to infect the elderly in greater numbers, with concurrent circulation of a B strain, a type that typically causes less severe illness. Influenza B can also affect seniors and is the strain that most often infects children.
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“Normally in a season, we’ll see a peak of influenza A happening some time towards the end of December or through January,” Murti said Monday. “And as that is coming down toward the end of February, that’s when we start to see that peak of influenza B activity into the spring and later season.”
But this year’s B strain, known as B/Yamagata, began circulating in the fall, much earlier than is usually the case, said Dr. Danuta Skowronski of the BC Centre for Disease Control.
B.C. is currently seeing about an atypical 50-50 mix of H3N2 and B/Yamagata, although other regions in Canada may have different ratios of the two strains affecting their populations, Skowronski said from Vancouver.
In its weekly FluWatch report, the Public Health Agency of Canada says there were 11,277 laboratory-confirmed cases of flu across the country as of Dec. 30 – about 70 per cent attributed to H3N2 – with more than 1,000 influenza-related hospitalizations and 34 deaths.
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However, Murti said those figures are an underestimate of the actual number of cases, as most people don’t seek medical attention for flu and, therefore, aren’t tested. As well, not all provinces and territories keep track of hospitalizations due to influenza.
“Looking at our numbers over the last couple of weeks and knowing there’s a bit of a reporting delay, we’re certainly on the upswing right now in terms of increasing activity for flu,” she said. “So probably in the next few weeks, we’re going to continue to see increased activity.”
Murti predicts the peak in H3N2 cases, at least, will likely come in the next few weeks.
“But you really don’t know the peak until you’re coming down the other side,” she said.
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