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The question over how influenza is transmitted is an important one because much of our arsenal against a pandemic will be NPI's (Non Pharmaceutical Interventions); masks, gowns, gloves, and social distancing.
Last fall, in an article in the Journal of Emerging Infectious Diseases, we were told that a review of the literature indicated that aerosol spread of influenza was probably a bigger factor than we thought.
Today, we get a different view.
This report by Maryn McKenna writing for CIDRAP.
Review finds little evidence of airborne spread of flu
Maryn McKenna
Contributing Writer
Mar 13, 2007 (CIDRAP News) – A rigorous review of research into influenza transmission concludes that the virus is overwhelmingly transmitted at close quarters, a finding that discounts the likelihood of airborne transmission and could have important implications for pandemic planning.
In the April 1 issue of Lancet Infectious Diseases, published online ahead of print, Gabrielle Brankston and colleagues of Toronto's University Health Network describe their evaluation of 32 experimental and observational studies that they sifted out of 2,012 citations addressing flu transmission in the English-language literature.
They come to two conclusions. First, that despite more than 70 years' research, much of what is believed to be known about flu transmission is based on poorly structured studies or faulty interpretations of results.
And second, that the preponderance of the robust evidence supports flu being acquired only within a short distance of an infected person—making it much more likely that the virus is transmitted by large respiratory droplets that fall out of the air within several feet, rather than by fine aerosols that can travel long distances and hang in the air for extended periods of time.
"Our final conclusion was that we cannot say flu is transmitted over long distances, and the only way flu can transmit over long distances would be through the airborne route," Dr. Michael Gardam, an epidemiologist and the study's senior author, said in an interview. "It really seems to transmit via close contact, which is traditionally understood to be droplet or direct or indirect contact. We cannot rule out airborne transmission, but we see no evidence of airborne transmission—and so we think it is unlikely to be a major player in the overall epidemiology."
CIDRAP (Center for Infectious Disease Research and Policy) is headed up by Dr. Michael Osterholm at the University of Minnesota. If their site isn't on your daily hit parade, it should be.
Maryn McKenna is, quite simply, one of the best avian flu reporters in the business.
The debate isn't over, by any means. We have conflicting published opinions, and not a lot of solid research to back up either position.
Dr. Osterholm has expressed skepticism over the conclusions in reached in this study. Again, quoting from this article:
"From my 30 years of experience I've always been impressed with how seasonal flu functions on a community basis as an aerosol-transmitted disease," he said. "We can see outbreaks in areas separated by hundreds of miles; that's much more consistent with an aerosol-transmitted pathogen—though that doesn't prove aerosol transmission. Pandemics have marched around the world in weeks to months in eras before we had jet planes. That smacks much more of an agent that's transmitted by the aerosol route."
Until we have proof positive one way or another, I'm assuming that airborne (aerosol) transmission of the virus is possible. When you have a pathogen as lethal as the H5N1 virus, it only makes sense to assume a worst-case scenario, and take proper precautions. Even if that means over protecting yourself.
I will continue to hope that the authors of this report have it right, and the virus is unlikely to be transmitted except through close exposure. But until we know for sure, that's an assumption I'm not willing to make.
Because when you are dealing with a deadly influenza virus, if you're wrong on something like this, you run the risk of being dead wrong.
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