To Your Health: Why Covid Is Short-Lived On Porous Surfaces!

Part-time Telluride local, Dr. Alan Safdi, is a world-renowned internist and gastroenterologist with encyclopedic knowledge of mind-body wellness and preventative medicine. He posts regularly on Telluride Inside… and Out under the banner of “To Your Health.” Dr. Alan’s blogs feature the most current information in his fields: health, wellness and longevity.

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This week, Dr. Alan curated a story about a recent study explaining why Covid is short-lived on porous surfaces.

For Dr. Alan’s regular posts and podcasts, go here.

Respiratory droplets evaporate faster on porous surfaces than on impermeable surfaces, a contributing factor behind why SARS-CoV-2 does not live long on surfaces like cloth and paper, according to a study published in Physics of Fluids.

“Based on our study, we recommend that furniture in hospitals and offices, made of impermeable material, such as glass, stainless steel, or laminated wood, be covered with porous material, such as cloth, to reduce the risk of infection upon touch,” Sanghamitro Chatterjee, PhD, a postdoctoral researcher at the Indian Institute of Technology, said in a press release.

In the study, Chatterjee and colleagues placed 1 µl droplets of pure water on a variety of porous and impermeable surfaces — which were chosen by the researchers to allow them to feasibly compare virus titer measurements from previous studies — and recorded them using high-resolution cameras. Optical microscopy was also used to evaluate porous surfaces.

The researchers defined virus survival time as the length of time the virus titer decayed to an undetectable level in previous studies. They compared the timings from previous studies with their findings.

Chatterjee and colleagues determined that droplets remain in liquid form for less time on porous surfaces compared with impermeable surfaces.

On both types of surfaces, 99.9% of liquid from droplets evaporated within a few minutes. However, a microscopic thin residual liquid film, in which the virus could survive, is left on solid parts of both impermeable and porous surfaces.

Chatterjee and colleagues found that this film evaporated much faster on porous surfaces due to the fibers of these surfaces and the void spaces in porous materials. Based on previous titer measurements, the researchers determined that the virus survival times were 4 days for glass, 7 days for plastic and 7 days for stainless steel. They noted that this ratio of virus survival time agreed qualitatively with their experiment on droplet evaporation.

For porous surfaces, they determined that the virus survival time was 3 hours on paper and 2 days on cloth, based on previous virus titer measurements. In their experiment, they found that the thin film lifetime was approximately 60 hours on cloth, which the researchers noted reasonably agreed with the previously observed virus survival time. On paper, they determined that the thin film lifetime was approximately 5 hours, which they noted was also reasonably consistent with the previously observed virus survival time.

“The fact that just the geometric features rather than the chemical details of the porous material make the thin-film lifetime significantly less was surprising,” Rajneesh Bhardwaj, PhD, an associate professor of mechanical engineering, IIT Bombay, said in the press release.

Chatterjee S, et al. Phys Fluids. 2021;doi:10.1063/5.0037924.

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Dr. Alan Safdi is board-certified in Internal Medicine and in Gastroenterology and is a Fellow of the American College of Gastroenterology. A proven leader in the healthcare arena, he has been featured on the national program, “Medical Crossfire” and authored or co-authored numerous medical articles and abstracts. Safdi has been involved in grant-based and clinical research for four decades and is passionate about disease prevention and wellness, not just fixing what has gone wrong. He is an international lecturer on the subjects of wellness, nutrition and gastroenterology.

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