The second wave of the first influenza pandemic of the 21st century may have peaked in Canada, according to a new analysis of flu activity nationwide.
The number of hospitalized cases, admissions to intensive-care units and deaths decreased in the week ending Nov. 21, the Public Health Agency of Canada said in its latest surveillance report.
The proportion of tests that were positive for flu was 34 per cent, lower than the three previous weeks. And, while the rate of flu-like illness is still much higher than expected for this time of year, every measure used to monitor the pandemic indicates flu activity is falling.
According to the report, "A possible epidemic peak has been reached by all provinces and territories."
University of Ottawa virologist Earl Brown said he is hopeful the trend will continue, "and we will not see further large increases in infection."
People should still expect to see low levels of activity as the winter proceeds, he said.
But the growing number of resistant people in the population, either because they were exposed to human swine flu or are being vaccinated against it, could "break the back of the pandemic" he said, "and leave most of the rest of us unscathed."
As recently as last Wednesday, federal officials said that while the number of H1N1 cases was "levelling off" in some parts of the country, the peak of the second wave had not yet been reached, and warned Canadians against becoming complacent.
"In reaching the plateau of the second wave in some communities, it does not mean the pandemic is over," said Dr. David Butler-Jones, Canada's chief public health officer.
"There is still the other side of the peak and there remain millions of infections to be prevented."
Sixty-one new deaths were reported in the week ending Nov. 21, down from 84 deaths reported the previous week. As of Nov. 26, 309 H1N1 deaths had been reported to the Public Health Agency of Canada.
Little is known about who is dying. From the start of a pandemic the World Health Organization warned threatened "all of humanity," people have been mostly left to ask: Who is really at risk?
The government provides only a brief summary, breaking cases down by sex, the median age of those who died and the proportion known to have had an underlying medical condition. Even then, no information is provided on whether the pre-existing condition was something such as cystic fibrosis, or mild, well-controlled asthma.
It is also not clear how many of the people who have died were outside the vaccination priority groups.
Federal data provided to Canwest News Service show that 62 per cent of the deaths in the first wave, from April through to the end of August, occurred in those age 45 and older, and the pattern has repeated itself in the latest wave.
While the under-20-year-olds continue to be the ones most likely to be hospitalized with H1N1, those 45 and older have the highest death rates per 100,000 people.
Nationwide, those 45 and older had hospitalization rates in the second wave that were nearly five times higher than during the first wave, and the death rates for the same group have been three-times higher in the second wave compared to the first.
Canadian critical-care doctors probing the worst cases of swine flu began reporting in August that 40-year-olds, many previously healthy, appeared to be most at risk of developing severe H1N1 disease.
But healthy adults ages 19 to 64 were not included in the priority groups the federal government recommended get the vaccine first when the shots began to be released Oct. 26. Nor were seniors 65 and older. Most provinces only began opening vaccinations to the general public in the past week or two.
It is also not clear whether the death statistics are painting a true picture of H1N1's toll. A review by Newfoundland's chief medical examiner released last week found that, of 15 people whose deaths were attributed to the pandemic virus, only five died as a direct result of H1N1.
In the 10 other deaths, some had cancer; others died suddenly in the community in a way more consistent with sudden cardiac death.
The federal government said any information for H1N1-related deaths must come from the provinces.
The provinces said privacy concerns prevent them from providing details.
But this leaves major gaps in the information about the true risks of H1N1 that are available to the public.
"In principle, the more information, the better," said Dr. Khaled El-Emam, Canada research chair in electronic health information at the University of Ottawa.
"But, in practice, I think it comes back to risk communication. How do you communicate the risks appropriately to the public? How do you communicate the risks so that you don't make things seem much worse than they really are, or much better than they really are?"
Dr. Simon Avis, Newfoundland's chief medical examiner, said he wanted to clarify whether the people reported of dying of H1N1 actually died of it or with it.
He reviewed 15 deaths of people who tested positive for H1N1, checking their medical records, reviewing autopsy findings and speaking with the attending physician.
Of the 15 cases, "only five you could say died as a direct result of H1N1 infection," Avis said.
Four out of the five were female. Only one had no underlying medical condition. Three had underlying lung disease, "some of it quite innocent asthma, " Avis said. "Others had quite severe lung disease."
"These individuals died of a respiratory death," he said. They ranged in age from 29 to 58.
In the other 10 cases, "some of them had metastatic cancer," Avis said. In one case, an autopsy confirmed no evidence of viral pneumonia. "There was evidence, however, of underlying cardiac disease that the individual was unaware of."
There were no discrepancies between what the review found and what the physician recorded on the death certificate as the major cause of death.
But, because all tested positive for H1N1 at the time of death, all deaths were reported to the Public Health Agency of Canada.
"It would be almost impossible to say (H1N1) had no effect" on the people who died of other conditions, Avis said.
"Anytime you have one disease, and you have another disease on top of it, that other disease is not going to make things better. But it's very difficult to say absolutely it had a role, or absolutely it didn't have a role."
But some died suddenly. "A sudden death in the community is not what you would expect from any type of influenza death," Avis said. "Usually the person presents with an illness, and gets progressively worse.
"The fact that a person dies very suddenly automatically makes you think, 'How would H1N1 cause that?' "
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