What kind of DIY face masks adequately reduces droplet dispersion? – Medical Information Bulletin

The researchers compared different types of DIY face masks to surgical masks to evaluate their effectiveness in reducing the spread of droplets from the nose and mouth.

SARS-CoV-2, the virus that causes the COVID-19 pandemic, is transmitted through droplets released by infectious patients when they speak, cough, and sneeze. Face masks reduce the spread of viral droplets from infectious people and can also protect healthy people from inhaling droplets. Many countries now recommend the use of face coverings by the general public in situations where social distancing measures can be difficult, e.g. B. in public transport or in shops.

DIY face masks recommended for the general public as an alternative to surgical masks

Because of the need to ensure an adequate supply of medical masks to health workers and frontline workers, public health authorities such as the Centers for Diseases Control (CDC) in the United States have proposed the use of DIY face masks for the general public. Various types of materials and designs for DIY face masks have been suggested, but little evidence exists as to how well they work. Researchers from the University of New South Wales, Australia conducted a video case study to compare different types of DIY face masks with surgical masks. They recently published their results in Thorax.

Double layer mask more effective than single layer in reducing droplet distribution

Using a healthy volunteer, researchers compared the effectiveness of a three-layer surgical mask and single-layer and two-layer DIY cotton cloth masks in reducing droplet spread. The single layer mask was made using a "quick cut t-shirt no-sew" method and the two-layer mask was made according to the sewing method described by the CDC. The researchers measured the droplet shedding using an LED lighting system and a high-speed camera to film the droplet distribution. The volunteer was filmed speaking, coughing and sneezing with any type of face mask and also without a mask.

The surgical mask was most effective in reducing the spread of droplets when speaking, coughing, and sneezing. A two-layer cloth DIY mask was more effective than a single-layer mask at reducing droplet spreading during these activities, although even a single-layer mask had some benefits.

Recommendations should recommend multiple layers

The study shows the value of using face masks and the differences between different types of masks. While this is only a single case study, the researchers recommend that DIY mask instructions recommend using multiple layers of material (at least three) for people who can wear a mask. According to the CDC, "Fabric face coverings should NOT be worn by children under the age of 2 or by anyone who has difficulty breathing, is unconscious, incapacitated, or otherwise unable to remove the mask unaided." The researchers also find that there are other factors that affect the usefulness of DIY masks, including the type of material used, the design and fit of the masks, and the frequency of washing. They say more study is needed to improve the design and use of DIY masks.

Written by Julie McShane, MA MB BS

References

1. Bahl P., Bhattacharjee S., de Silva C. et al. Face Covering and Mask to Minimize Droplet Distribution and Aerosolization: A Video Case Study. Thorax Online first published: July 24, 2020. doi: 10.1136 / thoraxjnl-2020-215748

2. BMJ press release July 23, 2020. Homemade face masks likely require at least two layers to contain the spread of COVID-19. https://www.eurekalert.org/pub_releases/2020-07/b-hfm072220.php

Image by Lukáš Jančička from Pixabay

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