Earlier this year, medical experts have categorized COVID-19 as a severe acute respiratory syndrome, a part of the coronavirus family along with SARS and MERS. A recent study published in the Centers for Disease Control and Prevention (CDC)'s journal, Emerging Infection Diseases, gives insight on the environmental conditions which affect the stability of the virus.
M. Jeremiah Matson, a student from the Marshall University Joan C. Edwards School of Medicine, led the team to discover what stabilizes the virus within a patient's sputum and nasal mucus. They describe in the study the importance of temperature.
SARS-CoV-2 strands were significantly longer in surface nasal mucus and liquid sputum at 4°C, the typical temperature in a home refrigerator. However, at 27°C, a little warmer than room temperature, the higher humidity level, and warmth caused the virus to be less stable.
The team accomplished this by mixing virus pathogens with nasal mucus and sputum samples. These specimens were then exposed to three varying sets of temperature - 4°C, 21°C, and 27°C - and relative humidity (RH) for one week. The four and 21-degree environments both had a 40% RH while the warmest setting was 27°C/85% RH.
The viral DNA, which is not infectious on its own, was present in the samples for the entire duration of the experiment. However, the infections virus was only detectable within 12 to 48 hours depending on which environmental conditions the samples were exposed to. After the computation of their results, they predicted that the virus can remain infectious in both mucus and sputum on surfaces for more than 10-12 hours even in humid and warm temperatures.
Reused N95 Mask
Matson was also involved in another study evaluating the effectiveness of a decontaminated and reused N95 mask against coronavirus. They compared four different decontamination methods of personal protective equipment.
Due to the worldwide shortage of N95 respirators and the high rate of infection transmission in hospitals, medical health workers could not dispose of masks after a single usage but had to regularly decontaminate them. Previous guidelines of decontaminating masks include UV light, ethylene oxide, vaporized hydrogen peroxide (VHP), gamma irradiation, ozone, and dry heat.'
The team explored UV light, 70% dry heat, 70% ethanol, and VHP decontamination. The N95 contains two main parts, the strip of stainless steel and the porous fabric, which was more difficult to decontaminate. In conclusion, the best, rapid inactivation of the SARS-CoV-2 virus while preserving the N95 mask's integrity was a combination of ultraviolet light and VHP.
Virus Stability
Commenting on the virus stability study, Matson said, 'the COVID-19 pandemic has been a sobering reminder that infectious diseases continue to be a major public health threat and require sustained research commitment.' He continued, 'while this is a small study that only addresses the potential for fomite [an object that may be contaminated with infectious agents] transmission, which is thought to be less important than droplet transmission for SARS-CoV-2, it nevertheless is informative for public health risk assessment.'
Researchers have yet to determine the 'stability in relationship to infectious dose for humans.' There are several other factors to consider such as infection duration and transmission alongside environmental conditions.
