The Frontal Cortex

Nylon hosiery and surgical masks? While I always assumed that the flu virus spread mainly through dirty door knobs and friendly handshakes, I was wrong. According to Lawrence Wein, “the dominant mode of virus transmission for influenza is aerosol — implying that hand washing will make little difference. This is consistent with the views of leading researchers several decades ago, views that have somehow been forgotten by the public health community.”

So what should we do?

The single most effective intervention is face protection. And because roughly one-third of influenza transmissions occur before an infected person exhibits symptoms, these precautions should be taken whenever people are in the same room throughout the pandemic period.

There are two kinds of face protection: N95 respirators, as worn by construction workers, for instance, and surgical masks of the sort worn by dental hygienists. (The respirators cost roughly a dollar apiece, the surgical masks 10 cents.) Their efficacy in preventing aerosol transmission depends on three factors: the extent to which the face filter prevents virus particles from passing through, how tightly the device fits and — most important — how long people can be coerced into wearing them.

To our surprise, we found that the filters in surgical masks, although not as good as the filters in N95 respirators, are still quite effective. And although a surgical mask fits much more loosely and allows more leakage, it’s also more comfortable — and therefore likely to be effective because it’s used more. Wearing nylon hosiery over a surgical mask essentially eliminates the face leakage, making this combination a practical, albeit macabre, alternative. The less comfortable N95 respirators would probably result in lower compliance.

Update: For an in-depth review of the flu-mask story, see this great Aetiology post from earlier this year.


  1. #1 Tara C. Smith
    October 25, 2006

    …views that have somehow been forgotten by the public health community.

    *sigh* I wish it was as black and white as he makes it out to be, but it’s simply not. I discussed this previously here, and it contains links to other sources of info on masks and influenza as well. I think masks–if used properly and consistently–could indeed help curtail influenza spread in the event of a pandemic (combined with distancing and other mechanisms he suggests), but it’s silly to say that public health has “forgotten” aerosol spread just because handwashing is emphasized. Handwashing is tried and true at preventing many respiratory diseases, and it’s easy to do. Masks are a much more complicated issue.

  2. #2 Jonah
    October 25, 2006

    Thanks Tara. I’ve updated my post. As usual, you make some great and pertinent points.

  3. #3 ERIC JUVE
    October 25, 2006

    I just got my box of 20 N95 style respirators. about $18.00 including shipping. I will mostly use them in my shop and I had intended to use them while in the company of someone ill. I would have difficulty wearing them in public, but that may well change if a pandemic happens.

  4. #4 Jun
    October 26, 2006

    There are two kinds of face protection….

    No there’s not. There are also P100 masks (i.e. even better than the N95 masks):

  5. #5 revere
    October 26, 2006

    I haven’t seen the work that Wein says he did with his graduate student, so I’ll reserve judgment a bit. It may be useful to know he is an Operations Research person and has done some good work on smallpox spread but what basis he has for opining on a subject that there is much debate about amongst virologists and infectious disease people I’m not sure. I read the Times op ed with some incredulity as it makes it sound much more definitive than I read the literature.

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