Face masks much more protecting in opposition to COVID-19 than face shields, warn CDC consultants
Researchers at the Centers for Disease Control and Prevention (CDC) conducted a study showing that face masks and neck gaiters were much more effective at reducing the release of breath aerosols that could potentially transmit Severe Acute Respiratory Syndrome 2 (SARS) seem to be as face protection -CoV-2).
SARS-CoV-2 is the causative agent of the current 2019 coronavirus disease (COVID-19) pandemic, which continues to pose a persistent threat to global public health and the economy.
Using a cough aerosol simulator to expel small aerosol particles into various face coverings, the team found that the N95 ventilator, procedural mask, cloth mask, and neck gaiters were effective at reducing the emission of aerosols, while the face shield did not.
“Our results suggest that face masks and neck gaiters are preferable to face shields as source control devices for cough aerosols,” write William Lindsley and colleagues.
A pre-print version of the paper is available on the medRxiv * server while the article is being peer-reviewed.
Cough aerosol simulator system for source control measurements. The system consists of an aerosol generation system, a bellows and a linear motor to generate the simulated cough, a flexible skin head shape on which the face mask, neck seal or face shield is placed, a 105 liter collection chamber into which the aerosol is coughed and a Andersen impactor to separate and collect the aerosol particles by size.
Community transmission can be through infected aerosol droplets
SARS-CoV-2 can be transmitted from person to person via large breathing aerosols (diameter larger than approx. 10 µm), which occur when an infected person coughs, sneezes, breathes, speaks or sings.
However, smaller aerosols are also released during these activities, suggesting that short-range airborne viruses may also be transmitted.
To protect themselves from this potential community route of transmission, various public health agencies, including the CDC and the World Health Organization (WHO), have recommended the public wear face masks or other face coverings as version control devices.
“Source control devices are designed to protect other people from infectious aerosols emitted by the wearer, compared to personal protective equipment such as N95 respirators, which are primarily designed to protect the wearer,” the team explains.
However, people often don’t like wearing face masks, and compliance levels can be low and inconsistent, the researchers say.
Individuals can repeatedly remove, replace, and further adjust the mask, which can contaminate the hands. This potentially leads to the transmission of the virus, especially in cases where the masks are reused.
Face shields have been proposed as an alternative
In an opinion piece in the Journal of the American Medical Association, the researchers suggested that face shields may be more effective at reducing transmission in the community because they are more comfortable and therefore more likely to be widely adopted by the public.
However, a few studies have examined face shields as source control devices and lack quantitative data on effectiveness.
What did the current study include?
Now, Lindsley and colleagues have used a cough aerosol simulator to eject a cloud that simulates small breath aerosols (0 to 7 µm in diameter) into various types of face coverings and assess the amount of particles that could move through and around each device.
Researchers tested the collection efficiency (the amount of aerosols blocked by the device) of an N95 ventilator, a medical procedure mask, a commercially available 3-layer fabric face mask, a polyester neck seal, and a commercially available disposable face shield.
Neck gaiters are worn either as a single layer of fabric or as a folded two-layer fabric. For the experiments conducted in this study, the researchers tested both configurations.
Face masks and gaiters were much more effective than face shields
On average, the N95 ventilator prevented 99% of all cough aerosol from being expelled into the environment, while the procedural mask blocked 59% and the cloth mask blocked 51%.
The neck gaiter blocked 47% of the cough aerosol when worn as a single layer and 60% when worn as a double layer.
The face shield, however, only prevented 2% of the cough aerosol from being released into the atmosphere.
There were no significant differences in the collection efficiency of the procedural mask, cloth mask, and neck seal, but all of these devices were significantly more effective than the face shield.
“Our results suggest that face coverings as source control devices are more effective than face shields in reducing the release of breath aerosols into the environment as a public health measure and in reducing the transmission of SARS-CoV-2 in the community,” the team concludes .
* Important NOTE
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or be treated as established information.