Drying time of COVID-19 virus respiratory droplets plays a major role in infectivity of COVID-19Â
In a new research, investigators examined the drying time of respiratory droplets from COVID-19 infected subjects and inferred that temperature, humidity and surface play vital roles in the infectivity of COVID-19.
How long the coronavirus causing the disease remains alive after someone infected with it coughs or sneezes has been a major query in the scientific community. Once the droplets carrying the virus evaporate, the residual virus dies quickly, so the survival and transmission of COVID-19 are directly impacted by how long the droplets remain intact. The droplet size is of the order of human hair width, and the researchers examined frequently touched surfaces, such as door handles and smartphone touchscreens.
Findings were published in Physics of Fluids, by AIP Publishing.
Using a mathematical model well established in the field of interface science, researchers compared the drying time of COVID-19 virus infected respiratory droplets on various surfaces in six cities – New York, Chicago, Los Angeles, Miami, Sydney and Singapore. Results showed higher ambient temperature helped to dry out the droplet faster and drastically reduced the chances of virus survival. In places with greater humidity, the droplet stayed on surfaces longer, and the virus survival chances improved. In the cities with a larger growth rate of the pandemic, the drying time was longer.
(left) A droplet on a surface. (right) Comparison of the growth rate of the infection of different cities/regions (bars) with respective drying times (squares) of a 5-nanoliter droplet. The error bar represents the variability in outdoor weather. CREDIT : Rajneesh Bhardwaj and Amit Agrawal
“In a way, that could explain a slow or fast growth of the infection in a particular city. This may not be the sole factor, but definitely, the outdoor weather matters in the growth rate of the infection,” said Rajneesh Bhardwaj, one of the authors.
The study suggests that surfaces, such as smartphone screens, cotton and wood, should be cleaned more often than glass and steel surfaces, because the latter surfaces are relatively hydrophilic, and the droplets evaporate faster on these surfaces.
