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SophiaZoe over at A Pandemic Chronicle takes a closer look at the recent study, published in the Chicago Journal Clinical Infectious Diseases, where researchers isolated aerosolized influenza viruses in the ambient air of an emergency room.
Influenza and airborne transmission
by SophiaZoe on January 22, 2009
There has been a long-standing gap in our understanding of the mechanisms behind the transmission of human influenza. Yep, that’s right, we do not know exactly what the major route of transmission is. That’s a strange reality given we regularly send men and women into space and bring them back, yet we cannot definitively state how the majority of flu infections are acquired.
Do we catch “the flu” from people coughing and sneezing on us? What about collecting our change from the cashier harboring an active infection? Or, do we risk infection by simply breathing the same air as someone with influenza? Are all three routes of infection? Which one poses the most risk to the uninfected? Are there degrees of danger of infection, or does each route carry equal risk of transmission?
A recently published paper, Measurement of Airborne Influenza Virus in a Hospital Emergency Department, Francoise M. Blachere, et al.1 informs us of findings that will help us close our knowledge gap on influenza transmissions.
Meanwhile, the Clinician's Biosecurity Network at the University of Pittsburgh Medical Center (UPMC) has a report on this study as well. This summary is easy to read, and is highly recommended as well.
A Hat tip to Sally on Flutrackers for this link.
CBN Report
Is Airborne Spread of Influenza Possible?
By Amesh A. Adalja, MD, January 23, 2009A new study1 from researchers at West Virginia University demonstrates that the influenza virus is able to remain suspended in the air, thus enabling airborne transmission. This finding suggests the possible need for more stringent infection control measures to forestall spread of seasonal influenza within hospitals.
<big snip>
The results of Blachere’s study call into question current recommendations for utilizing only droplet precautions when caring for patients with influenza. Given the presence of aerosolized virus, hospital air itself may be contaminated and act as a vector for spread of the influenza virus, just as hospital air can spread tuberculosis.
The big unanswered question for me out of all of this is one of viral load. In other words, how much aerosolized virus is one likely to be exposed to from an airborne route?
That we can detect influenza viruses in the ambient air of an emergency room is an important finding. Whether that proves that one can become infected (or how often it really happens) by breathing, or being exposed to that air, is another matter.
And that, I would surmise, is largely a matter of quantity and viability. Basically: How much flu virus material is actually floating in the air?
Of course, we don't know exactly what constitutes an infective viral load (no doubt, this varies greatly from person to person).
Differences in immune systems, age, genetics, and even how deeply one breathes, may make a huge difference.
Proving once again, there are no simple answers, or one-size fits all solutions.
For now, however, the evidence seems sufficient to call into question the practice of simply protecting against droplet infection alone.
N95 or better protection is looking more prudent as we travel down this learning highway.
