# 3443
Like many observers, I find myself more than a little mystified by what appears to be a very low CFR (Case Fatality Ratio) of this swine flu virus.
Given the number of `estimated’ infections around the world, we’d expect to see more deaths than have been reported to date.
A lot more.
Admittedly, the numbers we get are pretty vague, and I’ve limited faith that surveillance is picking up anywhere near all of the swine-flu related deaths around the globe. Still . . .
While citing `limitations’ in their study, researchers at the University of Otago in Wellington, New Zealand have suggested that the true CFR of this virus may be much lower than we normally see with seasonal flu.
Not because this virus isn’t particularly virulent – but because it doesn’t seem to attack the elderly – who are the most likely to die when stricken by influenza.
By striking a younger and generally stronger cohort, this virus – for now, at least - seems to be exacting a much lower death toll than we would normally expect.
But among young adults and children, the hospitalization and death rates appear to be higher than we normally see.
It is probably too early to place bets on any of these conflicting studies. They are all based on incomplete data, estimates, and assumptions.
Which explains the wide divergence in results.
We’ve also a long way to go in the evolution of this pandemic, and things may well change over time.
The novel H1N1 virus may mutate, and make adaptations to humans, that make it more virulent – or expand the age range that it attacks.
Additionally, the ultimate death toll will hinge greatly on the attack rate – the percentage of the population that is sickened by this virus. Estimates run anywhere from 3 to 5 times more than in a normal flu season.
But once again, we’ll have to wait and see.
Jason Gale of Bloomberg brings us the story.
Swine Flu May Be Less Lethal Than Earlier Estimated, Study Says
By Jason Gale
July 6 (Bloomberg) -- Swine flu, which has spread to 114 countries since April, may be at least 40 times less lethal than an earlier estimate, researchers in New Zealand said.
The probability of dying from the pandemic flu strain may be 1 in 10,000 cases and possibly as low as 1 in 100,000, doctors at the University of Otago in Wellington found. They applied four methods to calculate the proportion of fatal cases, and compared the results with an earlier estimate based on data from Mexico of 4 in 1,000.
Fatalities would be more common if the new A/H1N1 virus mainly affected the elderly, for whom flu usually poses the greatest risk, the scientists said in a study published in the journal Eurosurveillance last week. Gauging the pandemic’s ability to kill and cause serious disease is a key measure in assessing and determining how to respond to the threat, said co- author Michael Baker, an associate professor of public health at the university.
“The implications are potentially huge in terms of where you focus your effort responding to this,” Baker said in a July 2 telephone interview. “One of the reasons why this influenza pandemic might be having a very low case fatality is simply because it is infecting mostly younger people.”
The pandemic bug appears to be as contagious as seasonal influenza, and is spreading faster among people aged 10 to 45 years, according to the World Health Organization. The severity of the disease ranges from mild symptoms such as sore throat and muscle ache to severe illnesses including pneumonia that can result in death, WHO said.
Eurosurveillance, Volume 14, Issue 26, 02 July 2009
Rapid communications
The emerging influenza pandemic: estimating the case fatality ratio
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