Via CMAJ: High H1N1 prevalence and mortality rates a concern. Excerpt:
Type A (H1N1) influenza, the most common flu virus in Canada this year, has a higher than anticipated mortality rate causing some experts to wonder if it's virulence has increased.
The worrisome factor at this point "is the reported mortality rate in Alberta," says Dr. Pierre Lebel, an infectious disease specialist at the McGill University Health Centre in Montréal, Que. As of Jan. 13, there were ten confirmed deaths in Alberta attributed to type A (H1N1) influenza, as well as one in British Columbia, six in Saskatchewan, six in Ontario, one in Quebec and two in Nova Scotia.
"There are more deaths than what we expect for the regular H1N1 influenza," says Lebel. The strain this year could be more virulent than in past years, but it's too early to know for sure, he adds. This year's virus is now being sequenced with the aim of detecting mutations that might cause higher levels of virulence.
Regardless, the best protection is vaccination, says Lebel, particularly for those who are at a high-risk of developing bad flu. This year's flu shot protects against the type A (H1N1) virus among others. People who were exposed to H1N1 during the 2009 pandemic, either by acquiring the virus or through immunization, can get infected again due to slight variations in the virus.
According to the Public Health Agency of Canada (PHAC), 96% of this year's lab-confirmed influenza is type A (H1N1). The virus is unusual in that it appears to affect younger people more than other strains of seasonal influenza. People aged 20 to 65 are being hit harder than usual, comprising 52% of flu cases. Normally, 80% of people who die from seasonal flu are 65 years of age or older, but during the 2009 H1N1 pandemic, between 62% and 85% of those who died were younger than 65.
The prevalence of Type A (H1N1) influenza this year is worst in Western Canada, from Saskatchewan to British Columbia, says Dr. Michael Gardam, director of infection, prevention and control at the University Health Network in Toronto, Ont. "However, they're all through the peak. The worst of it is done."
In Canada, seasonal flu normally contributes to approximately 20 000 hospital admissions and between 4000 and 8000 deaths annually.