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Oct 14, 2020
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Coronavirus on the street: chances of infection

We figure out how high the chances of contracting COVID-19 are in an open space: just walking down the street or attending a public event.

Epidemiological data indicate that infection with the SARS-CoV-2 coronavirus occurs more often indoors and in transport. The US Centers for Disease Control and Prevention (CDC) guidelines indicate that outdoor exposure is lower. It is easier to comply with COVID-19 prevention measures on the street, including social distancing. In many countries, measures to ease quarantine were based on this assumption: outdoor events began to be allowed to be held.

Experts on the risk of contracting coronavirus on the street

There is currently no scientific evidence to support that COVID-19 can be contracted simply by walking down the street. But scientists believe that this is not so impossible.

Lindsey Marr of Virginia Tech told AFP that she recommends wearing masks outside if there are a lot of people. In her opinion, which she, however, does not consider an absolute rule, it is necessary to resort to a protective measure if you pass by one person per minute.

“When we walk among people on the street, we can catch the air they breathe out. Each individual breath poses a low risk, but this impact can accumulate over time, ”she said.

Wearing a mask outdoors is considered the safest strategy by Yale professor Kristal Pollitt. She reminds that passers-by can sometimes literally sneeze at each other.

The Rospotrebnadzor recommendations are consistent with these statements. The agency advises wearing a mask outdoors, since social distancing is not always possible.

Scientific evidence for outdoor coronavirus infection

A group of British scientists analyzed the existing evidence of the possibility of COVID-19 infection in open spaces. A review of them is published on medrxiv.org, a resource for hosting preprints.

In one of the studies reviewed by the authors, Japanese scientists indicated that the risk of infection outdoors is 18.7 times higher than the same risk indoors. This work looked at how many people had infected 110 SARS-CoV-2 infected people.

A study by Chinese scientists, which took into account cases of infection outside the province of Hubei, which is hardest hit by the coronavirus, found that among 7,324 infections, only two people were infected on the street. The virus was transmitted during a conversation. The reviewers find this data particularly reliable, citing the quality work done by the Chinese health care system to track infections. In both studies, it was about the likelihood of infection before the introduction of quarantine measures, that is, in ordinary life.

The most extensive information scientists have received from research database of the London School of Hygiene and Tropical Medicine. It contains information on more than 20 thousand cases of infection. Only 6% of coronavirus infections and 7% of COVID-19 clusters were associated with outdoor transmission (in whole or in part). Infections took place at sporting events, outdoor parties, markets and rallies. Increased risk was associated with shouting and singing.

What factors increase the risk of infection at outdoor events

Crowd density

Important factors predicting the risk of infection are the density of the crowd and the location of the people in it. Close contact, in which you can get an infection, is considered to be:

  • at a distance of less than two meters for 15 minutes;
  • less than a meter away for five minutes face to face;
  • less than a meter away for one minute without face-to-face contact;
  • skin contact.

People circulation

The more people move in the top, the higher the likelihood of transmission. An infected person who moves can infect more people. At sports competitions, people often sit without changing seats, and at festivals they have more contact.

Event size

The more people come to the event, the higher the risk that they will be infected. Scientists point out that the degree of this risk is related to the incidence of COVID-19 in a particular area.

Duration of the event

Plays a role as the duration of the event itself (competition or concert), and concomitant crowds (queues, visits to the toilet and bars).

Scientists point out that all factors are equally important. So, with a large crowd of people, the risk can be reduced by increasing the distance and restricting movement. Longer activities are safer when there is less concentration of people.

conclusions

The available information suggests that it is indeed much more difficult to get infected with COVID-19 outdoors than indoors. This is facilitated by natural social distance and generally accepted in society ideas about personal space. Better air circulation in open spaces also plays a protective role, which prevents the formation of high concentrations of aerosol containing viruses.

In certain cases, these protective factors can "fail" and infection becomes possible. Therefore, on the street, it is necessary to remember about the prevention of COVID-19: monitor the distance, wear a mask if necessary, and behave prudently at public events.


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