Canadian doctors probing the
worst cases of swine flu in Canada have made a striking finding: 40-year-olds, many previously healthy, appear most at risk of developing severe H1N1 disease.
The finding is based on global reports of illness and case reports from critically ill patients in intensive care units across the country. The investigation confirms the virus behind the
first flu pandemic of the 21st century does not fit the typical patterns of influenza.
Significant, doctors say,
is its ability to cause serious disease in previously healthy people.
"Although there are certain people who become critically ill with this virus that have co-morbidities,
it has been remarkable for its ability to cause illness in patients that don't have chronic illness and are not weakened from some other medical condition," says Dr. Robert Fowler, assistant professor in the departments of medicine and critical care medicine at the University of Toronto.
"
That's novel. It
makes it difficult, therefore, to define a segment of the population that is so-called high-risk and should maybe therefore be considered for vaccination before other groups, or potentially for early therapy before other groups," said Fowler, a member of the Canadian Critical Care Trials Group.
The researchers are working with the
Public Health Agency of Canada and various provincial groups to try to learn more about what predicts severe illness with H1N1, "and what we're going to need to treat patients as they come in greater numbers in the fall," Fowler said.
The picture that is emerging shows:
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Of those who have become critically ill with H1N1, the most commonly affected age is around 40. "They're surprisingly young," Fowler told Canwest News Service. Seasonal flu normally is most dangerous to the very young and those over age 65.
Among critically ill cases of H1N1, there is a spike in numbers in the under five group. But the median age for severe illness requiring critical care is around 40.
Experts suspect people over 65 have some immunity to the pandemic virus, because they were likely exposed to a distant cousin of H1N1 that circulated in the 1950s.
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Only about a third of patients who required critical care had a major underlying illness. Normally people most at risk of life-threatening flu complications are those with chronic underlying health problems, particularly lung illnesses such as emphysema.
With H1N1, most critically ill patients "will have something on their past medical history list, but often not that big a deal," Fowler said. "
Two-thirds of patients don't have serious co-morbidities when they're getting critically ill. Some are absolutely healthy and have no past medical history."
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Patients who become critically ill frequently develop severe lung injury, requiring not just mechanical ventilation, "but really extraordinary forms of mechanical ventilation" for prolonged periods, up to weeks at a time, Fowler said.
Many need high-frequency oscillatory ventilation, a form of ventilation that allows very high pressures to be built up in the airways to completely open up the lung, and provide optimal gas exchange. "
Some academic intensive care units will have maybe one, or two, maybe at most three, but most intensive care units across the country have none," Fowler said.
"
We're calling every hospital in the country to do an inventory of the number of ventilators that exist," he said. "
Our concern is that our capacity to deliver care will be challenged like it hasn't really been before," Fowler said. "It's not as though you can say, come back tomorrow, we'll try to book your appointment in a month, or a week. You need it now, or you're not going to make it."
Cities and hospitals may have to share resources as the pandemic hits at different times in different parts of the country, he said.
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Critically ill patients often need to be heavily sedated, and frequently receive medications to completely relax their muscles so they don't fight or work against the ventilator. "They're often in a bit of a state of suspended animation for the period that they're most ill," Fowler said.
"Pandemics of the early part of the 20th century may have wiped out a huge number of people around the world ? which was horrible ? now, many of these patients would and will be saved by aggressive support in an intensive care unit," Fowler said. "
The challenge is that we now will have intensive care units that are being asked to save these patients in a way, and at a volume, that we've never had to work with before."
The
findings will be presented next week at a two-day meeting in Winnipeg of national and international critical care and public health experts to discuss the care and management of severe H1N1 disease and prepare for the expected fall pandemic wave.
http://www.canada.com/news/national/Swine+hits+healthy+year+olds+hardest/1932592/story.html
