dcyphr | Effect of various decontamination procedures on disposable N95 mask integrity and SARS-CoV-2 infectivity


This study was done to see if a disposable N95 mask can be sanitized and reused. Being able to reuse N95 masks would help with the shortage of masks for healthcare workers. Vaporized hydrogen peroxide, ultraviolet light, and ethanol were all tested as decontaminants. The best decontaminant was determined by how well the masks were decontaminated and how well the physical material of the masks held up, known as integrity.


As we know, the SARS-CoV-2 has become a global pandemic. This has caused a high demand in hospitals for personal protective equipment. Due to how SARS-CoV-2 spreads, the N95 mask is a very effective piece of protective equipment. N95 masks are often used when the healthcare worker is trying to protect themselves from a respiratory disease. The N95 mask is supposed to be a one time use mask. But, in these desperate times many healthcare workers have to reuse their masks if they want to stay protected. Some healthcare workers are sanitizing the masks with whatever decontaminant they can find. However, the effect of these household decontaminants on the mask's structural integrity have not been tested on the N95. There have been previous studies done on how vaporized hydrogen peroxide, ultraviolet light, and ethanol affect the function of the N95 mask. However, the decontaminants have not been tested on how well they kill the SARS-CoV-2 if it is on the N95 mask. In this study, they test how well the decontaminants will kill SARS-CoV-2 present on the masks and if it affects the mask's ability to function.



First, they tested the integrity of the mask after the treatment with vaporized hydrogen peroxide, ultraviolet light, and 70% ethanol. This test used a respirator to measure the air particles inside and outside of the mask. A FIT score was calculated based on the ratio of particles inside to particles outside. A FIT score of over 100 means the mask is safe to use in a hospital setting. The FIT score of a new, untreated N95 mask is about 200, so it is well beyond the minimum requirement of 100. The ethanol and ultraviolet treatments lowered the FIT scores, but still averaged over 100. The vaporized hydrogen peroxide maintained a high FIT score without altering the function of the N95 mask.


Second, the vaporized hydrogen peroxide, ultraviolet light, and ethanol were tested to see how well they would decontaminate the mask from SARS-CoV-2. Nose swabs from SARS-CoV-2 positive patients were collected and applied to N95 masks. Then, the masks were decontaminated using the three methods. After decontamination, the masks were dipped in a liquid solution of cell culture media. Dipping the masks allowed any of the viral RNA to be transferred into the cell culture media. The media containing viral RNA can now be tested to see if the decontamination worked. The viral RNA was found in every mask that SARS-CoV-2 nasal swabs were applied to. Just because RNA was found, doesn’t mean the virus is alive and infectious. To test if the RNA was still infectious, a cell culture was treated with the RNA positive media of each sample. These cells were grown for four days in an incubator. Then, the level of RNA was tested again. There were lower levels of RNA in the vaporized hydrogen peroxide and ultraviolet light samples compared to the samples which did not go through decontamination. In the samples that had been treated with ethanol, zero RNA was detected.


Three factors are necessary for a mask to be considered safe for decontamination and reuse. The decontaminant must be safe for human use, successfully kill the virus, and maintain the function of the mask. Ethanol had the worst integrity of the mask after treatment, but was very effective against the viral RNA test. With the ethanol treatment, the decrease in function of the mask was time dependent. So, 30 minutes after treatment with ethanol, the mask was less functional than 4 hours after treatment. Throughout the entire time span, the average FIT test was still over 100. Overall, all decontamination strategies did lower the amount of viral RNA present. Though this study is consistent with prior research, there are some clear limitations that should be noted. First, the viral RNA test was only done once because of lack of time, risk of exposure to SARS-CoV-2, and lack of resources. Another limitation is that there are several types of N95 masks, and this study only tested N95 types 1860 and 1870+(healthcare grade), and 8511(non health care grade). The different mask types had slightly different outcomes and this may be due to the fluid resistant coating on the healthcare grade masks. This study did not test the effect of the decontaminants on the fluid resistant coating specifically. Due to the way the FIT test measures mask fitness, it also may have given a false low fitness of the treated masks. The viral RNA test may not also be accurate compared to a real healthcare setting. This is because 100microliters of the SARS-CoV-2 positive nasal swab solution was applied directly to the mask. This is a large volume compared to a couple of droplets landing on the mask after a patient coughed. So in actual practice, vaporized hydrogen peroxide and ultraviolet light would most likely be very effective in decontamination.The study confirms that the decontamination of the N95 mask does reduce the function of the mask. This is not normally recommended for N95 use, but these are unprecedented times. If there was a mask shortage, this study can help guide healthcare providers to safely consider mask decontamination.