Friday, March 14, 2014

Surgical mask, N95 mask...

A response to the following article:

With the current evidence, surgical mask is non-inferior to N95 respirators in preventing influenza infection, the basic reason for its existence in modern healthcare -- preventing droplet-transmitted infections[1]. It should be noted that there are multiple reason behind wearing surgical masks, such as preventing the wearer's droplets from contaminating the operating field, or decreasing the amount of droplets emitted during e.g. sneezing.
On the other hand, while there are a lot of Taiwanese and Japanese people wearing cloth mask. While there are not a lot studies on this matter, Rengasamy et al provided some evidence that it doesn't really work[2]. It's not good enough trapping anything from influenza to tuberculosis.

While we all know that we can buy N95 masks and simple surgical mask, the need for fit-testing for the use of N95 masks are often forgotten: one need to have a tight-fitting N95 masks to enjoy the benefit of a respirator: how is it different from a mask? A major difference lies in that a surgical mask filters aims at filtering only a portion of air taken by the person whereas a respirator aims at filtering all, i.e. practically all gas that you inspire went through the N95 if you are wearing it correctly.

Let me repeat it: you need to do a fit-testing to determine which N95 model fits you the best. If an N95 is not fitting, you are not enjoying any of its benefits. A simple rule is, if it feels easy wearing it, either you are working in the industry, or you are wearing it wrong.

There are some studies suggesting that N95 fit-test is not necessary[3]. However, this has not been published in a peer-reviewed journal, thus, without further studies, it is probably wise to continue doing fit-tests. A rule of thumb for those who may not have access to fit-testing is, 1860 for gentlemen, and 1860s for ladies. Your mileage may vary.

[1] JAMA. 2009 Nov 4;302(17):1865-71
[2] Ann Occup Hyg. 2010 Oct;54(7):789-98.
[3] ICAAC 2009; Oral session K-1918b

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