More than two-thirds of those who have fallen critically ill and died of H1N1 influenza in Canada are younger women, according to a startling new study that underscores that while the pandemic flu is mild overall, in selective cases it is brutal and lethal.
The research, published in the Journal of the American Medical Association, highlights that there are two distinct forms of the disease: In 99 per cent of cases, people get sick, stay home for a few days, and get better. But in about one in every 1,000 cases, patients become gravely ill and require staggering amounts of care.
"What the public needs to understand is that people who are getting critically ill with H1N1 look just like you and me - they're essentially healthy people," Anand Kumar of the Canadian Critical Care Trials Group, said in an interview.
In fact, the research reveals that the large majority of those who became seriously ill had no serious underlying health conditions, contrary to what is often stated.
The study group did an in-depth examination of 168 patients - 67 per cent of them female - who were admitted to Canadian intensive care units for treatment of influenza A H1N1 between March and July of this year.
One in six of those patients admitted to an ICU died - 72 per cent of them women. Their average age was 42. That is in stark contrast to seasonal flu where virtually all deaths occur in people over the age of 65.
Older people seem to have partial immunity because of exposure to a similar strain of virus. But Dr. Kumar said it is not clear why younger women are so hard hit.
"One interesting observation is just how ill these people get. I've never seen people so ill in ICU," said Dr. Kumar, who is also an intensive care specialist at Winnipeg Health Sciences Centre.
According to the study, 81 per cent of H1N1 patients in ICU had to be placed on a ventilator, 14 per cent received inhaled nitric oxide (a rare treatment used for those in severe respiratory distress) and 4 per cent were so ill that they were placed on extracorporeal membrane oxygenation (ECMO, a machine that usually substitutes for the heart and lungs during heart surgery).
"These are intensely labour-intensive therapies. The resources required to treat these patients are astronomical," Dr. Kumar said.
According to the research, of the first 7,107 reported cases of H1N1 in Canada, 1,441 required hospitalization (20.3 per cent) and 278 were admitted to ICU (3.9 per cent).
Of those admitted to intensive care, 67.3 per cent were female and 29.8 per cent were children. The average age of those in ICU was 32. Another notable statistic is that 25.6 per cent of those who fell gravely ill were aboriginal.
"The spring outbreak of 2009 influenza A (H1N1) infection in Canada affected primarily young, female and aboriginal patients without major co-morbidities [unrelated health conditions]" the researchers said in summarizing the situation.
While most studies to date have emphasized that those who died of H1N1 influenza had "underlying conditions," the new Canadian data show that only 30.4 per cent of those who fell gravely ill had severe health problems such as chronic obstructive pulmonary disorder, congestive heart failure and cerebral palsy. For the most part, those who died had commonplace health concerns like obesity, high blood pressure and smoking.
The study confirmed that pregnant women are at particular risk of falling seriously ill if they contract swine flu.
The Canadian research was one of three studies published yesterday by JAMA.
A second paper , which examined the cases of 58 critically ill swine flu patients in Mexico, found that the death rate there was twice as high as in Canada - 41 per cent - in large part because of lack of access to sophisticated ventilator technology.
The third research team, in Australia and New Zealand, look specifically at the effectiveness of using ECMO as a form of life support, and it found that 80 per cent of patients survived.
In an editorial published in JAMA, Douglas White of the department of critical care medicine at the University of Pittsburgh, said the research provides a sobering taste of what the health system will have to face if there is widespread infection with H1N1 influenza, and it underscores the need for having adequate intensive care beds.
"Clinical outcomes will depend on clinicians' ability to apply sophisticated mechanical ventilatory support," Dr. White said.
He also cautioned that hospitals and health systems "must develop explicit policies to equitably determine who will and will not receive life support should absolute scarcity occur."
About 4,500 people worldwide have died of H1N1, including 79 in Canada, according to the World Health Organization.
There have been more than 375,000 laboratory-confirmed cases of swine flu, but many countries, including Canada, have stopped counting individual cases because disease is so widespread.