Coronavirus: Studies Find Steam Effective in Sterilizing Used Medical Masks

Researchers in China and Houston show that steam sterilization processes do not damage surgical masks or N95 respirator masks.

Two new studies show steam can effectively decontaminate medical masks including the N95 respirator mask.

Shortages of personal protective equipment (PPE) such as N95 respirators have plagued the U.S. response to the coronavirus disease 2019 (COVID-19) pandemic. On Feb. 22, testimony before Congress asserted that 3.5 billion N95 masks were needed for healthcare workers during the pandemic, and there was about 1% of that figure available.

Houston-based researchers who produced a small-scale study on reprocessing N95 respirators with steam say reusing sanitized masks is crucial in countries facing PPE shortages.

"With each attempt to safely don a contaminated N95 mask, the risk for infection of vital clinicians grows. In countries where equipment shortages have progressed, healthcare workers are currently being infected with COVID-19 at three times the rate of the general population, reducing the ability of hospitals to provide adequate care, and increasing COVID-19 patient death rates. Thus, it is essential to create a protocol for sanitizing masks without reducing efficacy."

Moist heat is among the most promising COVID-19 decontamination methods, according to the Centers for Disease Control and Prevention.

Chinese steam sanitization study

A research team in China published a study in the Journal of Medical Virology on using steam effectively to sanitize surgical masks and N95 respirators.

The sanitization process, which used avian coronavirus of infectious bronchitis virus to mimic the new coronavirus, was simple. Contaminated masks were placed in plastic bags and steamed over boiling tap water in a kitchen pot.

"The avian coronavirus was completely inactivated after being steamed for 5 minutes," wrote the Chinese researchers, who conducted the study at the College of Veterinary Medicine, Qingdao Agricultural University, Qingdao, China.

The effectiveness of the masks was unaffected by exposure to steam as long as two hours, the Chinese researchers wrote. "In this study, mask decontamination with steam on boiling water is without abrasive physical or chemical action. This can account for its excellent performance in maintaining the masks' blocking efficacy."

In addition to not damaging the masks, the steam treatment has other benefits, they wrote. "This measure has other advantages including safety, not requiring special agents or devices, and rapid inactivation of most microbes potentially attached to the surface of masks."

Houston steam sanitization study

Researchers at Houston Methodist Research Institute in Houston published a steam sanitization study for N95 respirators in the journal Infection Control & Hospital Epidemiology. The study featured five test subjects to verify mask fit after the decontamination process.

The immediate-use steam sterilization (IUSS) procedure was more complex than the Chinese research team's steaming method.

• Used N95 respirators were placed in paper-plastic sterilization peel pouches manufactured by Mechanicsville, Virginia-based Medical Action Industries Inc.
   
• The N95 respirators were steamed in a Steris Amsco Evolution HC1500 PreVac Steam Sterilizer autoclave
   
• Chemical and biological indicators were used to ensure there was no contamination after the steaming procedure

The N95 respirators were not damaged in the steam sterilization procedure, the Houston-based researchers wrote. "Five test subjects were used to begin to account for individual differences between faces. For each subject, a fit test was performed before the IUSS cycle to serve as a control value. Fit tests were performed after three IUSS. In all cases, masks retained their structural integrity and efficacy."