Coronavirus: Who gave you COVID-19? It’s not who you think

COVID-19 has sparked fierce debate about the risks posed by that careless stranger in the grocery aisle, post office or sidewalk.

But there’s a growing body of evidence that it’s close contact during gatherings of beloved friends and family that is most likely driving the spread of the novel coronavirus.

Brief interactions — like passing by someone during a walk outside — don’t seem to be the primary force behind the epidemic, based on what we know so far from contact tracing studies.

“Studies indicate that close and prolonged contact is required for COVID19 transmission,” said Dr. Muge Cevik, a respected infectious diseases clinician and researcher from Scotland’s St. Andrews University, in an analysis of COVID-19 clusters posted on Twitter.

“The risk is highest in enclosed environments: household, long-term care facilities and public transport,” she wrote. The highest risk is within the first five days of symptoms, she added.

While casual, short interactions are not the main driver of the epidemic, “keep social distancing!” she urged.

Here are some examples of how the coronavirus has spread in the past few months:

Households: Compared to other contacts, people living in the same house as an infected individual have a higher chance of being infected.

A study from Shenzhen, China found that 11.2% of household contacts developed COVID-19, compared to 6.6% for all close contacts. Another study from China had similar findings: When checking the contacts of 105 COVID-10-positive individuals, the researchers found 16% of contacts in the same household tested positive for the virus.

An Illinois woman with symptoms spread the virus to her husband. Of the other 347 actively-monitored close contacts that interacted with these two patients, 43 developed symptoms and none tested positive for the coronavirus.

Family gatherings: In Chicago, the coronavirus was most likely spread from one infected person to other people — not from the same household — at a funeral in February and a birthday party three days later. Both events were several hours long and the infected individual, who had symptoms, embraced others and shared food. In total, this single individual caused six confirmed and nine probable COVID-19 cases.

Group gatherings: Public health officials believe that one infected individual spread the virus to choir members in Skagit County, WA. Of the 61 people who were at a 2.5-hour choir practice in early March, there were 32 confirmed and 20 probable COVID-19 cases.

Restaurants: In a restaurant in Guangzhou, China, one infected individual may have spread the coronavirus to customers at two neighboring tables. The tables overlapped for about an hour. The report’s authors think that infectious droplets spread between the tables via airflow from the restaurant’s air conditioning system.

Homeless shelters: In early April, tests in a Boston homeless shelter showed that the virus had infected 147 residents, or 36% of the shelter’s population.

So there’s no need to fear the passing stranger — but don’t invite them home for drinks.

Lisa M. Krieger contributed to this article.