Dr. Anand Kumar, intensive care unit attending physician for the Winnipeg Regional Health Authority, looks at the monitor of a ventilator at the St. Boniface Hospital in Winnipeg. ((Canadian Press/John Woods))

Many of the Canadians who died or were sent to hospital earlier this year with H1N1 virus were young adults, female and aboriginal, a new study suggests.

The study, published in Monday's online issue of the Journal of the American Medical Association, looked at 168 patients with confirmed or probable swine flu. So far, one in five patients hospitalized with the virus has ended up in an intensive care unit or ICU.

Of the group, 24 or 14.3 per cent, died within the first 28 days of becoming critically ill, Dr. Anand Kumar, an intensive care specialist at the Health Sciences Centre and St. Boniface Hospital in Winnipeg and his colleagues found.

"Our data suggest that 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 study's authors wrote.

The ages in the mortality pattern were similar to that of the 1918 H1N1 Spanish flu pandemic, they said.

Other findings included:

  • 32.2 was the average age of patients.
  • 67.3 per cent were female.
  • 29.8 per cent were children.
  • 25.6 per cent were First nations, Inuit, Metis or aboriginal Canadians.
  • 81 per cent received mechanical ventilation.
  • 12 days was the average length of stay in ICU and on a ventilator.

The most common other illnesses that patients had were a history of lung disease or smoking, obesity, hypertension and diabetes.

Most of the ICU patients who died also had not taken antiviral drugs early enough.

Aboriginals 'cause for concern'

"The increased fraction of the aboriginal community presenting with severe 2009 influenza A (H1N1) infection is notable but not unique," the study's authors said, pointing to the three to nine per cent mortality in aboriginal communities from the 1918 Spanish flu pandemic, compared with less than 0.75 per cent in nonaboriginal communities then.

"Although mortality was not substantially greater among aboriginal Canadians in this report, the number of patients with severe disease and knowledge of prior illness patterns in this community is a cause for concern," the researchers said.

The tendency of females to develop severe infection was "striking," and has not been observed in other studies of the H1N1 pandemic, they said.

The reason is unclear, but the role of pregnancy has been noted in previous influenza pandemics. In the latest study, 7.7 per cent of the patients were pregnant.

Mexican patients died waiting for ICU bed

In most infectious diseases such as sepsis and septic shock, it's mostly males that are affected and have a higher mortality, the team said.

It's hoped that describing the risk factors, typical clinical features and response to therapy will help in recognizing, diagnosis and managing H1N1 infections.

The study included cases from most regions of Canada but many were from Manitoba's outbreak, which involved an aboriginal population.

Overall, a second study appearing in the same issue of 58 patients admitted to ICU in Mexico City with swine flu-related disease showed similar findings.

Mexican ICU patients also tended to be relatively healthy adolescents and young adults. An average of 12 days of mechanical ventilation and "rescue therapies" such as specialized ventilation and inhaled nitric oxide, were needed. 

The Mexico mortality rate was twice that of Canada's, and four Mexican patients died waiting for ICU beds.

"The investigators from both Mexico and Canada noted that the health care systems struggled to meet the demands created by the increased patient volume, a sobering observation given the absolute number of excess ICU admissions was modest," Dr. Douglas White, and JAMA editor Dr. Derek Angus, both of the University of Pittsburgh School of Medicine, said in a journal editorial.

The editorial authors suggests several ways for hospitals to respond to the unique needs of the sickest H1N1 patients, such as:

  • Regionalizing care to preserve resources at other hospitals for other patients.
  • Developing telemedicine consultations for doctors in outlying hospitals to check with experts.
  • Make temporary staffing changes at hospitals to ensure doctors who are experienced in handling these cases are always present.

In most cases, people get sick, stay at home and get better. But in about one in every 1,000 cases, patients become gravely ill and need to be hospitalized.

The findings should serve as an eye-opener for people who have dismissed swine flu as a mild form of influenza, said Dr. Michael Osterholm, an infectious diseases expert at the University of Minnesota. 

For many it is, but "for a very small number of patients, this illness is hell," said Osterholm, director of the Center for Infectious Diseases Research and Policy.

Last week, researchers in the U.S., Australia and New Zealand reported similar findings on the ages of the sickest H1N1 patients in those countries during the spring.

With files from The Canadian Press