- An important factor in virus transmission is how long it takes a droplet to evaporate because it
can’t survive in a dry environment. - The likelihood of SARS-CoV-2 surviving on a surface increases roughly 5 times in a humid environment compared to a dry one. Higher temperatures can kill the virus more quickly.
- Moisture-friendly surfaces, such as smartphone screens, cotton, and wood, should be cleaned more often than glass and steel surfaces since the droplets evaporate faster on these surfaces.
With the spread of the virus that causes COVID-19, behaviors previously considered strange have become commonplace: opening doors with our elbows, office workers wiping their desks with disinfectant, and use of hand sanitizer that borders on obsessive.
The virus is most often spread via respiratory droplets but can also be spread via contaminated surfaces.
SARS-CoV-2, the virus which causes COVID-19, can be spread by tiny droplets expelled from a person’s mouth or nose with a cough or sneeze.
Just
If a person with COVID-19 coughs or sneezes into their hand and then touches a doorknob, it means another person is at risk of developing the disease if they touch it.
Researchers have been wondering how a change in weather could affect the transmission of the virus.
While it seems clear that hot weather won’t stop the virus from spreading, new data finds it may help keep the virus from surviving for long periods of time on surfaces.
An important factor in virus transmission is how long it takes a droplet to evaporate, because it
Risk is associated with droplet drying time
New research published June 8 in the Physics of Fluids journal examines the drying time of contaminated droplets on various surfaces. This was done in six cities worldwide under different weather conditions to understand which areas may be at highest risk.
“Motivated by [the] ongoing COVID-19 pandemic, we conducted this research to understand the drying of respiratory droplets deposited on a surface because we know COVID-19 spreads through these droplets,” study author Rajneesh Bhardwaj, PhD, and associate professor at the Indian Institute of Technology in Mumbai, told Healthline.
“The droplets could be expelled from mouth/nose in the event of coughing, sneezing, or even talking,” he said. “Their size is on the order of width of [a] human hair.”
He explained these surfaces include those touched very often, such as a door handle or touch screen.
“The survival of virus inside the droplet is linked to [the] drying of the droplet since previous studies have shown that once there is no medium [droplet], the chances of the survival of the virus are much less,” said Bhardwaj.
Bhardwaj and his team analyzed droplet drying times under various outdoor weather conditions to find if this data is connected to the growth rate of the pandemic.
They looked at data from New York, Chicago, Los Angeles, Miami, Sydney, and Singapore and then plotted the growth rate of COVID-19 cases in those cities with the drying time of a ‘typical droplet.’
They discovered that in cities experiencing greater increases in cases, the drying time was longer.
“We were surprised a bit, since there seems to be a correlation between the outdoor weather and growth rate of COVID-19. In a way, that could explain a slow or fast growth of the infection in a particular city. Perhaps it is one of the factors in determining the growth rate,” said Bhardwaj.
According to study findings, the likelihood of SARS-CoV-2 surviving on a surface increases by roughly 5 times in a humid environment compared to a dry one, and higher temperatures can kill the virus more quickly.
“This can be illustrated by comparing the drying time of Singapore and New York City. The time is shorter for the former as compared to the latter, despite with a large humidity for the former (70–80 percent) as compared to the latter (50–60 percent),” the study authors wrote.
The findings also suggest that hydrophilic (moisture-friendly) surfaces, such as smartphone screens, cotton, and wood, should be cleaned more often than glass and steel surfaces, since the droplets evaporate faster on these surfaces.
Crowded areas will increase transmission risk
Bhardwaj believes these findings mean we must be much more careful about spreading COVID-19 during humid summer weather.
“Yes, this is a likely scenario since humidity may help to survive the droplet and the virus inside it for a longer time. Singapore data shows that there is a slight surge in number of daily infections in late May, perhaps due to the advent of Southwest Monsoon,” he said.
Two big factors could lead to an increase in cases in the United States — the reopening of businesses like casinos in Las Vegas, where people may crowd on the Strip, and the rise of protests against police brutality.
In some cases, protests were so large people were unable to physically distance. Additionally, as people have been arrested, they have reportedly been put in jail cells where they’re unable to keep a safe distance.
Experts say it’s possible we may see an increase in cases if people are unable or unwilling to physically distance.
“The center of a large crowd is no different than a sealed off, unventilated room filled with potentially infected individuals — many holding large signs which will block the flow of clean air,” said Dr. Stephen Berger, an infectious disease expert and co-founder of GIDEON (Global Infectious Diseases and Epidemiology Network).
“If even one carrier of COVID-19 was present at these gatherings, we can expect to see a wave of cases appearing during the next 2 to 14 days. Most will begin to experience symptoms 5 to 6 days after the event,” he said.
According to Berger, we can reduce this risk by taking common sense precautions.
“Those planning to attend additional protests and similar gatherings must, at a minimum, wear face masks and maintain social distancing as much as possible. Wash hands frequently and assume that the stranger standing next to you is spreading the virus,” he said.
The bottom line
Not only does the coronavirus spread by contact with contaminated surfaces, but new research finds that weather can influence how long the virus survives.
Scientists found that higher humidity could allow the virus to remain infectious longer on surfaces.
Also, the likelihood of SARS-CoV-2 surviving on a surface increases by about 5 times in a humid environment compared to a dry one, but higher temperatures can kill the virus more quickly.
Experts say this may mean mass protests currently underway could cause a new spike in COVID-19 cases. They also say this risk can be reduced if protesters use masks and follow physical distancing guidelines.
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