Sunday, 17 January 2021

Masks - from the Journal of Hospital Infection


Dismantling myths on the airborne transmission of severe acute respiratory syndrome coronavirus (SARS-CoV-2)

Tang et al, Journal of Hospital Infection, Jan 2021 pre print

Several laboratory studies have already shown that surgical and home-made masks are somewhat (but incompletely) effective in both limiting exhaled particles, and in protecting wearers from inhaling particles from others. Surgical masks can contain, and therefore reduce, the dissemination of viruses shed by an infected wearer by up to 3-4-fold (i.e. ∼67-75%), and even 100% in the case of seasonal coronaviruses., When an infectious person wears a mask or face covering, the size of the exhaled plume is also reduced and this also helps to reduce the risk of exposure to those nearby.
Surgical masks also protect the wearer, by reducing the exposure to incoming droplets and aerosols from infected individuals by an average of 6-fold (range 1.1 to 55-fold)., The filtration capacity of surgical masks in the micron size range is often considerable, although it varies between brands. We know that the filtration capacity of N95/FFP2 respirators is better if they have been appropriately fit-tested, to avoid leakage of aerosols around the side of the respirator into the breathing zone.
Even home-made cloth masks (made from tea cloths or cotton t-shirts) can reduce the exposure from incoming particles by up to 2-4-fold (i.e. ∼50-75%).
This mainly depends on how the mask is made, what materials it is made from, the number of layers, and the characteristics of respiratory secretions to which it is exposed. Based on the evidence supporting a role for airborne transmission of COVID-19, the use of N95/FFP2/FFP3 respirators by frontline healthcare workers should be recommended. For those that cannot tolerate wearing these masks for long periods, the less restrictive surgical masks still offer some protection, but it needs to be acknowledged that these won’t be quite so effective

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