Amid the coronavirus pandemic, health experts reiterate infection control measures, such as frequent hand washing, wearing masks, and social distancing, which are vital means to prevent infection. Many health agencies recommend covering the mouth and nose with cloth masks to prevent depleting the supply of medical and surgical masks among health care workers.
A team of researchers reports that cloth masks effectively protect against infection if they are washed every day. The researchers recommend daily washing of cloth masks at high temperatures to reduce the likelihood of contamination and transmission of viruses such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the coronavirus disease (COVID-19).
Efficacy of cloth masks in preventing viral infections
In previous randomized controlled trials (RCT) in hospital healthcare workers, cloth masks resulted in a higher risk of respiratory infections compared with medical masks. The current study was the only published RCT of cloth masks amid the coronavirus pandemic.
The study aims to perform a post hoc analysis of unpublished data on mask washing and contamination from the original RCT to provide a better understanding of the poor performance of two-layered cotton cloth masks used by healthcare workers in the previous study.
The original RCT was published in 2015 in the journal Infectious diseases and has been the only RCT ever conducted on the effectiveness of cloth masks in preventing viral infections. It was conducted in 2011 among hospital workers in Vietnam.
The team studied results from a subgroup of 607 healthcare workers in selected high-risk areas in secondary and tertiary-level hospitals in Hanoi, Vietnam. These healthcare workers used a two-layered cloth mask and were part of a trial comparing medical or surgical masks and cloth masks.
The team has found that if cloth masks were washed in the hospital laundry, they were as effective as surgical or medical masks.
“Both cloth masks and surgical masks should be considered ‘contaminated’ after use,” Professor Raina MacIntyre, a study co-author, said.
“Unlike surgical masks, which are disposed of after use, cloth masks are re-used. While it can be tempting to use the same mask for multiple days in a row or to give it a quick hand-wash or wipe-over, our research suggests that this increases the risk of contamination,” she added.
The study findings showed that viral contamination with rhinovirus was detected on both used medical and cloth masks. Most of the healthcare workers said they washed their masks by hand. The study also revealed that the risk of infection was more than double among those who washed their masks on their own, compared to the masks that were washed in the hospital laundry.
Further, the team discovered that there was no difference between surgical or medical masks and cloth masks that were washed in the hospital laundry.
“Using a self-reported method of washing, we showed double the risk of infection with seasonal respiratory viruses if masks were self-washed by hand by HCWs. The majority of HCWs in the study reported hand-washing their mask themselves. This could explain the poor performance of two-layered cloth masks if the self-washing was inadequate,” the authors wrote in the paper.
They added that cloth masks washed in the hospital laundry were as protective as medical masks. It is important to wash cloth masks daily using the proper method, which may reduce the risk of being infected with COVID-19.
Applicable to the public
Though people wearing cloth masks in the public are unlikely to be exposed to the same amount of pathogens like viruses as healthcare workers, the researchers still recommend washing cloth masks every day, especially for those who are working outside their homes or those who need to go outside.
COVID-19 is a highly infectious virus, and there is still more to learn about it. It is essential to take precautions to protect oneself against the virus, like making sure masks are effective.
“The WHO recommends machine washing masks with hot water at 60 degrees Celsius and laundry detergent, and the results of our analysis support this recommendation,” Professor MacIntyre explained.
“Washing machines often have a default temperature of 40 degrees or 60 degrees, so do check the setting. At these very hot temperatures, hand-washing is not possible. The clear message from this research is that cloth masks do work – but once a cloth mask has been worn, it needs to be washed each time properly before being worn again; otherwise, it stops being effective,” she added.
- MacIntyre, R., Dung, T.C., Chughtai, A., Seale, H., and Rahman, B. (2020). Contamination and washing of cloth masks and risk of infection among hospital health workers in Vietnam: a post hoc analysis of a randomized controlled trial. Infectious Diseases. https://bmjopen.bmj.com/content/5/4/e006577