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.