Catching coronavirus outside is rare but not impossible, experts say

A sticker on the pavement reminds pedestrians to social distance in London. AFP/Daniel Leal-Olivas

WASHINGTON - Almost all documented coronavirus transmissions have occurred indoors, but experts say that wearing a mask outside is justified because there is still a risk of infection.

The likelihood of catching the virus increases at events where people stand near each other and talk for long periods of time, such as parties or election campaign rallies.

In an analysis of 25,000 cases, which has not yet been independently reviewed, six percent of cases were linked to environments with an outdoor element, such as sporting events or concerts.

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These were enclosed areas where social distancing was not observed, or where people stayed for a while, moving around and talking loudly or singing.

"There were virtually no cases that we could identify that took place in sort of everyday life outdoors," study author Mike Weed, a professor and researcher at Canterbury Christ Church University, told AFP.

The data indicates that "outdoors is far safer than indoors, for the same activity and distance," according to a group of scientists and engineers, including professors from American, British and German universities.

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"The risk of transmission is much lower outside than inside because viruses that are released into the air can rapidly become diluted through the atmosphere," the group explained, comparing the virus-carrying "aerosols" to cigarette smoke.

Since February, multiple studies and health authorities have pointed to the airborne path of transmission, by invisible clouds of microscopic droplets (aerosols) that we release by breathing, talking and singing.

This is in addition to the relatively larger droplets that we expel by coughing or sneezing, which can land directly on someone else's face within a perimeter of one or two meters (up to six feet).

The smallest droplets float in the air for minutes or hours, depending on an area's ventilation. In a poorly ventilated room, but also outside between two buildings with no air circulation, the droplets can accumulate and get inhaled by a passerby.

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The time spent near a contagious person will be a key factor: a second on the sidewalk doesn't seem to be enough to catch COVID-19. It probably takes at least several minutes. 

On restaurant patios, the group of scientists recommends keeping a safe distance between tables and wearing masks while not eating.

In terms of public health, experts believe that it is ultimately more efficient to have simple and clear guidelines.

"Having a universal agreement of continued use of mask is really the safest strategy," said Kristal Pollitt, a professor of epidemiology and environmental engineering at Yale University.

Source
AFP