How long can coronavirus survive on difference surfaces?

In a paper in Physics of Fluids, by AIP Publishing, researchers have examined the drying time of respiratory droplets from COVID-19-infected subjects on various surfaces in six cities around the world. The droplets are expelled from the mouth or nose when someone with COVID-19 coughs, sneezes or speaks. The droplet size is in the order of human hair width, with researchers examining frequently touched surfaces, such as door handles and smartphone touchscreens.

Using a mathematical model well established in the field of interface science, the drying time calculations revealed that ambient temperature, type of surface and relative humidity play critical roles. Higher ambient temperatures help to dry out the droplet faster and reduce the chances of virus survival. In places with greater humidity, the droplet stayed on surfaces longer and virus survival chances improved.

Researchers determined the droplet drying time in different outdoor weather conditions and examined if this data connected to the growth rate of the COVID-19 pandemic. Researchers selected New York, Chicago, Los Angeles, Miami, Sydney and Singapore and plotted the growth rate of COVID-19 patients in these cities with the drying time of a typical droplet, finding that the drying time was longer in cities with a larger growth rate of the pandemic.

“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.

“Understanding virus survival in a drying droplet could be helpful for other transmissible diseases that spread through respiratory droplets, such as influenza A,” said Amit Agrawal, another author.

The study suggests that smartphone touchscreens, cotton and wood should be cleaned more often than glass and steel surfaces, as the latter surfaces are relatively hydrophilic, with droplets evaporating faster on these surfaces.

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