4 things you need to know about CDC's new stance in favor of wearing masks
As COVID-19 cases surge nationwide, the U.S. Centers for Disease Control and Prevention has new guidelines about the wearing of masks.
According to the CDC, the coronavirus infection is transmitted predominately by respiratory droplets generated when people cough, sneeze, sing, talk, or breathe.
The CDC is now recommending community use of multi-layered cloth masks to prevent transmission of the virus.
Below are a few things you should know about the new stance in favor of wearing masks:
1. Why are masks important:
Masks are primarily intended to reduce the emission of virus-laden droplets, which is especially relevant for asymptomatic or pre-symptomatic infected wearers who feel well and may be unaware of their infectiousness to others. These individuals are estimated to account for more than 50% of transmissions.
Masks also help reduce inhalation of these droplets by the wearer. The community benefit of masking for COVID-19 control is due to the combination of these effects; individual prevention benefit increases with increasing numbers of people using masks consistently and correctly.
2. How does wearing a mask protect you and others?
Multi-layer cloth masks block release of exhaled respiratory particles into the environment, along with the microorganisms these particles carry. Cloth masks not only effectively block most large droplets, but they can also block the exhalation of fine droplets and particles, which increase in number with the volume of speech and specific types of phonation.
Multi-layer cloth masks can both block up to 50-70% of these fine droplets and particles, and limit the forward spread of those that are not captured. Upwards of 80% blockage has been achieved in human experiments that have measured blocking of all respiratory droplets. In some studies, cloth masks performed on par with surgical masks as barriers for source control.
3. What kind of masks are best?
Studies demonstrate that cloth mask materials can also reduce wearers’ exposure to infectious droplets through filtration, including filtration of fine droplets and particles less than 10 microns.
Multiple layers of cloth with higher thread counts have demonstrated superior performance, compared to single layers of cloth with lower thread counts, in some cases filtering nearly 50% of fine particles less than 1 micron.
Some materials may enhance filtering effectiveness by generating triboelectric charge that enhances capture of charged particles, while others may help repel droplets and reduce fabric wetting and thus maintain breathability and comfort.
4. What is the "real-world" data regarding masks and transmission?
An investigation of a high-exposure event, in which 2 symptomatically ill hair stylists interacted for an average of 15 minutes with each of 139 clients during an 8-day period, found that none of the 67 clients who subsequently consented to an interview and testing developed infection. The stylists and all clients universally wore masks in the salon as required by local ordinance and company policy at the time.
In a study of 124 Beijing households with > 1 laboratory-confirmed case of SARS-CoV-2 infection, mask use by the index patient and family contacts before the index patient developed symptoms reduced secondary transmission within the households by 79%.
A retrospective case-control study from Thailand documented that, among more than 1,000 persons interviewed as part of contact tracing investigations, those who reported having always worn a mask during high-risk exposures experienced a greater than 70% reduced risk of acquiring infection compared with persons who did not wear masks under these circumstances.
A study of an outbreak aboard the USS Theodore Roosevelt, an environment notable for congregate living quarters and close working environments, found that use of face coverings on-board was associated with a 70% reduced risk.
Investigations involving infected passengers aboard flights longer than 10 hours strongly suggest that masking prevented in-flight transmissions, as demonstrated by the absence of infection developing in other passengers and crew in the 14 days following exposure.