A frequent discussion I have with friends concerns the difficulty people have in evaluating risk. Consider, for example, your relative risk of ending up on an airplane that terrorists attempt to hijack versus your risk of randomly picking up flu from another traveler on that airplane. We estimate the influenza-induced death rate in the U.S. as ballparking at around 30,000 people per year, which is rather higher than the death rate from terrorism of any kind. Naturally, there are other reasons why the United States maintains a policy of terrorism prevention, but at the personal scale this suggests your risk mitigation behaviors should focus significantly more on avoiding disease transmission and rather less on reprising Kurt Russell's role in Executive Decision.
Do you wear a mask to avoid flu? Should you? Does it work?
As it happens, many public health agencies have policies requiring the use of surgical masks as an infection barrier, but until this month there were no randomized, controlled trials on whether that policy makes sense.
As reported at the 49th Interscience Conference on Antimicrobial Agents and Chemotherapy, a randomized, controlled trial of nearly 2,000 health care workers in Beijing has given us our first real information on the value of masks in blocking transmission of respiratory infections. The upshot? Surgical masks are bunk, but there are real benefits from N95 masks.
The first randomized controlled clinical trial comparing surgical masks to fit-tested and nonfit-tested N95 masks in at-risk healthcare workers has found that the respirators were "clearly superior" in guarding against viral and respiratory infection, lead author of the study, C. Raina MacIntyre, PhD, from the University of New South Wales in Sydney, Australia, told meeting attendees.
"N95 masks should be the standard of care for healthcare workers who have a high risk for respiratory transmission," she said. "We need to protect our frontline health workers. I haven't seen a shred of evidence supporting any benefit from surgical masks. You might as well tell healthcare workers to wear nothing."
The study's results revealed that surgical masks offered no protection against respiratory illness or influenza. Yet N95 masks had a statistically significant efficacy of 60% against clinical respiratory illness, 75% against influenza, 56% against lab-confirmed respiratory viral infection, and 75% against confirmed influenza.
Fit testing, however, did not improve the efficacy of the N95 masks, Dr. MacIntyre announced.
"Given the logistic difficulties of fit testing, particularly during an infectious-disease emergency, this is an advantage for public-health control," the authors say in their abstract.
This is good news from many standpoints. First, it's always useful to know that your current policy directives don't have any evidence, as that lets you discard them and spend your resources more effectively. Second, it means that off-the-shelf N95 masks work just as well as custom-fit ones, which means you can get the full benefit during a pandemic using pre-stockpiled inventory.
The benefits from the N95 masks are fairly significant, and provide clear direction for future pandemic policies as well as personal decisions about wearing masks on airplanes and in other situations where it's hard to avoid respiratory contacts.
Note that this study was supported by 3M, which manufactures one brand of N95 mask. That said, the results are so significant and clear-cut that I'm not very concerned about conflict of interest (presumably they would have declined to report on the results if the N95s had turned out not to be effective).
From this Medscape article (free signup required for access)
Edited to add: Unfortunately this study has been retracted, with no word on why. The only remaining study does not show increased efficacy for N95s.
=