A new study suggests many of the Canadians who have died of swine flu or were placed in intensive care during the "first wave" were relatively young, healthy women whose condition deteriorated quickly.
While the number of patients studied for the research was small, the lead researcher, Dr. Anand Kumar of St. Boniface Hospital in Winnipeg, Man., said the results shocked him.
"It's worrisome and startling," he told reporters. "They are in the prime of their lives -- people between the ages of about 10 to 55 -- which is distinctly unusual."
The study, published online Monday by the Journal of the American Medical Association, looked at 168 patients with confirmed or probable infections of swine flu who were hospitalized in Canada between mid-April and mid-August.
The study found:
- the average patient was 32.2 years old
- 29.8 per cent were kids under 18
- 67.3 per cent were female
- 25.6 per cent were aboriginal
- 14.3 per cent died within a month of being hospitalized
- 17 per cent died within 90 days
- 29 died, most within two weeks of the first symptoms; 24 of them were women.
Unlike some previous flu pandemics, which saw high death rates among the very young and the very old, "severe disease and mortality in the current outbreak is concentrated in relatively healthy adolescents and adults between the ages of 10 and 60 years," the authors write.
The observation that Canadian women were at higher risk of severe illness is "striking," the authors said, noting that other swine flu studies have not noticed such a pattern.
"The explanation for increased risk of severe disease and death among females in this report is unclear but the role of pregnancy as a risk factor has been noted in previous influenza pandemics," the authors noted.
While the authors call the patients studied "healthy," it should be noted that 95 per cent had some underlying risk factor, such as asthma, smoking, obesity or high blood pressure.
The researchers found that once swine flu patients were sick enough to need hospital care, they declined very fast, usually requiring ventilators and advanced "rescue" treatments.
Patients who become severely ill had symptoms for about four days before going to hospital and then often required intense care in the ICU within one or two days; their average ICU stay was 12 days.
Shock and multi-organ failure were common; 81 per cent of the patients they studied needed to be put on ventilators.
Kumar said swine flu is one of the most difficult conditions he's ever had to treat.
He also said he normally sees only a few patients a year who become severely ill from the flu. But at one point in Winnipeg during the spring, 50 per cent of the available ICU beds in the city were filled with H1N1 patients, all "struggling for their lives simultaneously."
Higher death rate in Mexican hospitals
Another study also published Monday in JAMA looked at the experience of 58 swine flu patients hospitalized in Mexico. That study found the death rate among critically ill patients there was much higher -- more than double what was seen in Canada, at just over 40 per cent.
Dr. Rob Fowler, the senior author of both papers, suggests the Mexican death rate is a sign of what might happen in other developing countries that have fewer ICU beds and less access to advanced respiratory treatments.
Fowler, a critical-care specialist at Toronto's Sunnybrook Health Sciences Centre, says the studies also show that patients who were given antiviral medications were seven times more likely to survive than those who did not.
A related editorial in JAMA notes that the studies are not a true snapshot of the prevalence of swine flu, since "it is difficult to ascertain the incidence of H1N1 infection in the population and hence the true proportion of affected patients who require hospitalization, ICU admission, or rescue therapies."
But they say the studies provide clues on what hospitals can expect in the coming months as the second wave begins and what they must do to prepare.
JAMA published the studies and editorials early to coincide with their presentation at a meeting of the European Society of Intensive Care Medicine.
Health officials say the best way to prevent infection with swine flu is to get the vaccine when it becomes available in a few weeks.
Dr. Anne Schuchat of the Centers for Disease Control and Prevention said Sunday she's surprised by all the misinformation being circulated about the new vaccine.
She said the risks from not getting the vaccine are greater than any potential risks of the vaccine and that previous flu vaccine formulations have had excellent safety records.
