Flu cases on the rise in Canada despite expected fall

The federal government is reporting a sharp rise in influenza in recent months, at a time of the year when detected cases generally start to fall in Canada.

The government's latest FluWatch report says 2,121 laboratory detections of influenza, including 2,113 for influenza A and eight for influenza B, were reported during the week of May 8-14, most involving individuals under 45.

"The number of detections and the weekly percentage of tests positive for influenza have sharply increased since the beginning of April," the report says.

"This increasing trend in laboratory detections is unusual because laboratory detections are typically decreasing at this time of year."

TOTAL DETECTIONS BELOW PRE-PANDEMIC AVERAGE

Although a total of 8,998 influenza detections have been reported so far this season, between Aug. 29, 2021, and May 14, 2022, nearly all for influenza A, it is still lower than the pre-pandemic average of 46,070 generally seen by this point in the season.

However, the percentage of positive influenza tests in the most recent reporting week is above expected pre-pandemic levels at 12.6 per cent compared to between five and 11.9 per cent.

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The number of tests performed that week also is above the pre-pandemic average at 16,618 compared to 4,311.

Researchers have found that pandemic measures, put in place with the aim of slowing the spread of COVID-19, have helped stem cases of influenza.

"So our reduced contact rates may have interrupted transmission of other infectious diseases such as influenza," Canada's chief public health officer, Dr. Theresa Tam, said during a news conference on Friday.

"When most population public-health measures, like closures and capacity limits were removed, we saw COVID-19 transmission rates rebound and now we're seeing influenza activity increasing up to the seasonal threshold, despite the opposite trend being expected at this time of the year."

The influenza report says influenza-like illness (ILI) made up 1.8 per cent of all visits to health-care professionals during the last reporting week, exceeding pre-pandemic levels typically seen at that point in the year.

However, the report says ILI symptoms are not specific to any respiratory pathogen and could be due to influenza, SARS-CoV-2 or the virus that causes COVID-19, or other respiratory viruses.

"This indicator should be interpreted with caution as there have been changes in health-care seeking behaviour of individuals and a smaller number of sentinels reporting compared to previous seasons," the report says.

HOSPITALIZATIONS

During the last reporting week, there were 56 influenza-associated hospitalizations and three intensive care unit admissions as reported by nine participating provinces and territories.

Over the same week, 26 hospitalizations were reported in those 16 and under.

Influenza-associated pediatric hospitalizations are also rising, with a total of 152 reported, 64 per cent involving children under five. Seventeen pediatric intensive care unit admissions also have been reported.

So far this season, there have been 322 influenza-associated hospitalizations. The largest proportion, 39 per cent, were in adults 65 and older. There have been 28 intensive care unit admissions.

OUTBREAKS

In the last reporting week, there were five laboratory-confirmed influenza outbreaks, including two in long-term care facilities, two in facilities classified as "other," which may include private personal care homes, correctional facilities, and colleges or universities, and one outbreak in an acute care facility.

A total of 39 outbreaks have been reported so far this season, including 18 in long-term care, 15 in "other" facilities, three in remote or isolated communities, and three in acute care facilities.

Among outbreaks of influenza-like illness, three were reported in schools during the last reporting week and a total of 86 have been reported this season, all but one of which were in schools or daycares.

The report stresses that ILI outbreaks can be due to influenza or other respiratory viruses, including COVID-19.

"Many respiratory viruses in addition to the flu commonly circulate during the fall and winter, and can cause clusters of cases with respiratory illness which could be captured as ILI," the report says.

VACCINATION

Vaccine coverage for the flu this season appears to be similar to the 2020-21 season, with 30 per cent of adults between 18 and 64 years old reporting having received the influenza vaccine. This includes 27 per cent coverage among those without chronic medical conditions and 38 per cent in those with chronic medical conditions.

Seventy-one per cent of seniors 65 and older received the vaccine.

Earlier this year, CanAge, Canada's National Seniors' Advocacy Organization, gave the country a D- grade for its adult vaccination efforts during 2021 for non-COVID-19 preventable illnesses such as the flu and shingles. Many provinces also were lacking.

With files from CTVNews.ca writers Brooklyn Neustaeter, Tom Yun and Alexandra Mae Jones.