In a typical flu season, the Winnipeg hospitals where Dr. Anand Kumar works might see one, maybe two life-threatening cases of viral pneumonia caused by influenza.
So seeing 10, 15 and more flu patients in those same hospitals' intensive care beds in June is still a shock, suggests Kumar, a critical care specialist who works at three different hospitals in the city.
"You just don't see this many of them," Anand says of the patients, struggling to survive H1N1flu infections.
"You don't see rows and rows of patients on ventilators because they have respiratory failure, a viral pneumonia kind of thing. It's unusual."
At last count, Manitoba hospitals had 30 respiratory distress patients in the ICU, some confirmed H1N1 flu cases, others for whom tests are still pending.
In most people, H1N1 flu behaves like regular flu - it makes you feel miserable, you head to your bed and in time you recover. But in an as-yet unknown proportion of cases, the virus seems to quickly trigger severe illness.
A report compiled by the World Health Organization said between two and five per cent of confirmed cases require hospitalization. But no one yet knows how big a portion of the iceberg is above water (the confirmed cases) and how much remains submerged (cases that never come to the attention of medical authorities).
People who end up getting admitted to hospital are generally presenting with shortness of breath. And by the time they get to the ICU, swine flu patients - most much younger than your average hospitalized flu patient - are gravely ill from a viral assault on their lungs.
"They're getting very bad, bad respiratory failure," says Dr. Michael Gardam, head of infectious disease prevention and control for Ontario's public health agency.
Kumar and others describe patients whose care is challenging.
"The patients are difficult to manage. They're unusually difficult to ventilate effectively," he says, referring to the practice of putting patients who cannot breath adequately for themselves on a machine called a ventilator that takes over the job temporarily.
"They're just really, really sick. It's impressive how sick they are."
Researchers are still trying to piece together how the new H1N1 virus attacks the bodies of those who develop a severe swine flu infection, and whether the damage is all the work of the virus.
One theory is that an over-exuberant immune response turns the body's defences against itself. That has been seen in human infections with H5N1 avian influenza, but it's not yet determined if this process - sometimes called a cytokine storm - is at play with swine flu.
"We don't know right now how much is direct toxic effect of the virus versus the effect of the body's immune system," says Dr. Nathan Dean, chief of pulmonary critical care at LDS Hospital in Salt Lake City, where he's treated about 25 swine flu cases in ICU over the past month.
Ask Dean what's happening to his patients' bodies and the response is both quick and rueful: "I would love to know."
In addition to trying to keep these patients alive, clinicians like Anand and Dean are gathering data. The case studies they are writing, and which will shortly be competing for space in medical journals, will help doctors who haven't yet see severe swine flu cases know how to handle them when they do.
Likewise, autopsies that have been performed on a number of people who died of their infections will help scientists figure out what the virus does in the body, information physicians may be able to mine for clues on how to improve a severely ill person's chances of survival.
The additions to the scientific literature will be welcome.
Finding out what is going on with severely ill patients has been a struggle, says Dr. Frederick Hayden, an influenza expert at the University of Virginia who co-authored the recent WHO report.
"The information is very important in terms of understanding how to manage the more seriously ill patients," Hayden insists.
He says the emerging evidence - confirmed by Anand's and Dean's observations - is that at least a portion of the sickest of the sick are suffering from an aggressive viral pneumonia.
Seasonal flu often lays low the body's defences. In the case of some, particularly the elderly, that opens the door to what are called secondary bacterial pneumonias. When people succumb to seasonal flu, these bacterial pneumonias are often the direct cause.
But at least most bacterial pneumonias can be treated with antibiotics.
There are fewer drug options for viral pneumonia. Of the four antiviral drugs that target flu, this particular bug is resistant to two. That leaves oseltamivir and zanamivir - Tamiflu and Relenza.
For optimum efficacy, they should be started within 48 hours of onset of illness. But, as it recommended for cases of H5N1 avian flu, the WHO suggests longer and perhaps higher doses of antivirals for gravely ill swine flu patients.
People who cannot breath for themselves are placed on a ventilator, which can bridge the patient to recovery. But breathing machines can pose risks as well. A portion of people go on to develop ventilator associated pneumonia.
Beyond that, treatment options are limited.
"It's basically supportive (care)," says Gardam. "You're supporting them long enough for their lungs to heal."
While most so far have survived, the H1N1 flu death toll mounts daily. The ages of the dead are startling for influenza. Within the past several days, two healthy 40-year-old men died - in Winnipeg and in Chile. So did a 20-year-old woman in San Diego, Calif.
"The people who die in the short term die of acute severe lung injury, I think," says Dr. Allison McGeer, an influenza expert with Toronto's Mount Sinai Hospital.
"Now whether that's direct insult from flu, whether that's flu in combination with other viruses ... whether that's flu and bacteria - don't know."
