What’s Cooking? Face Mask Decontamination via Rice Cookers to Ward Off COVID-19

April 28, 2020

Medical investigators throughout the world are cooking up ideas that will hopefully put an end to COVID-19, sparing thousands of lives while bringing our old way of life back. (Maybe.) Count among them, investigators with the Louis Stokes Cleveland VA Medical Center, and the ideas they’re cooking up come right from the kitchen. 

In a pre-print article in the American Journal of Infection Control, the investigators found that rice cookers—an appliance found in kitchens all over the world—can decontaminate cloth masks, and they urge that further studies be conducted to see if the rice cookers could also decontaminate surgical and N95 masks as well. 

“Given the recommendation that cloth face masks be worn in public settings, steam treatment using these readily available kitchen items could provide safe and effective decontamination of cloth masks,” the investigators conclude.

One of the questions investigators wanted to answer: Which is better at decontaminating masks, moist or dry heat? They studied surgical face masks, 3M 1860 N95 respirators, and masks made of fabric that were being distributed to visitors and personnel who were not involved in direct patient care at a Cleveland area hospital. The test organisms were a clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA). Also included, a single-stranded RNA virus bacteriophage MS2. 

The article states that “10-μL aliquots containing 10 colony-forming units (CFU) or plaque-forming units (PFU) of the test organisms suspended in 8% simulated mucus were inoculated onto 1-cm areas on both the outer or inner surfaces of the respirators or face masks.”

The inoculated masks or respirators were put in a steamer for about 13 to 15 minutes, “including 8-10 minutes of heating and 5 minutes of steam. For comparison, inoculated masks or respirators were subjected to dry heat at 100°C for 15 minutes in an oven….”

The inoculated sections of the face masks and N95 respirators were then vortexed for 1 minute “in 1 mL of phosphate-buffered saline with 0.02% Tween and serial dilutions were plated on selective media to quantify viable organisms.”

The tests were performed in triplicate. Log10reductions were compared to untreated controls. A reduction of 3-log10 or greater in recovery of organisms from the masks or respirators was determined to be effective decontamination. 

Investigators wrote that “the steam treatment resulted in a greater than 5 log10reduction in bacteriophage MS2 and MRSA applied to the outer and inner surfaces of the face masks and respirators, whereas dry heat at 100°C for 15 minutes did not result in a greater than 3 log10reduction of either organism at any of the inoculated sites on any masks or respirators. No visible changes were observed in any of the masks or respirators after 5 cycles of decontamination.”

Put simply, rice cookers—with their moist heat—can decontaminate face masks; dry heat at the same temperature didn’t do as well, although further studies are needed to evaluate how well a rice cooker can decontaminate surgical face masks and N95 respirators. 

In terms of practical applications, one cannot get much more practical than a rice cooker, as the investigators note. When it comes to COVID-19, we’ve had to innovate, with healthcare facilities being “forced to adopt strategies to extend or reuse personal protective equipment (PPE) such as N95 filtering facepiece respirators and surgical face masks.” 

Cloth face masks are often worn many times between laundering. Ultraviolet light and hydrogen peroxide vapor have been tried. “However, sending used respirators to a central processing facility for hydrogen peroxide vapor treatment is likely to be labor-intensive and costly and ultraviolet light is suboptimal for decontamination of soft surfaces,” the article states. “There is an urgent need for simple and widely available methods to decontaminate PPE, including cloth masks.”