Coronavirus super-spreader events all have notable similarities — and they reveal the types of gatherings we should avoid for years

• An average person with coronavirus infects between 2 and 2.5 other people, but sometimes, an infected individual passes the virus to far more people during a "super-spreader event."
• There have been reports of super-spreaders in South Korea and the US; these events have sparked local outbreaks.
• Most super-spreader events are similar: The infected person attends an indoor gathering with lots of people, like a religious service, choir practice, or birthday party.
• The commonalities between these events inform health officials about the types of gatherings with the highest chances of facilitating the virus' spread.
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In mid-February, a 61-year-old woman attended church services in Daegu, South Korea. Soon thereafter, she tested positive for the coronavirus, then so did dozens of others. South Korea's coronavirus case count quickly jumped from 29 cases on February 15 to more than 2,900 two weeks later.

Throughout this pandemic, clusters of coronavirus infections like this have cropped up almost overnight, sprouting outbreaks that spiral out of control. Such spikes in cases can often be traced back to a super-spreader event like the one in Daegu, in which one individual infects an atypically large number of people.

So far, coronavirus super-spreader events have all shared a few key characteristics: They've mostly involved indoor gatherings in which lots of people from different households were in close, extended contact, such as religious services, birthday parties, and choir practices.

In that sense, it's not individual people who pose an inherent risk as "super-spreaders" or "super-emitters" — it's a certain type of activity, one that's unlikely to be considered safe again until we have a vaccine.

At least 43 people in the South Korean church got sick

A virus's R0 value (pronounced R-naught) refers to the average number of people that one sick person goes on to infect in a group that has no immunity. Experts use this metric to predict how far and how fast a disease will spread. The number can also inform policy decisions about how to contain an outbreak. The R0 of the coronavirus, so far, seems to hover between 2 and 2.5, according to the World Health Organization.

But the 61-year-old South Korean churchgoer, dubbed "Patient 31," may have infected at least 43 people after she attended services at Daegu's Temple of the Tabernacle of the Testimony on February 9 and 16. Followers of the fringe religious faction were asked to remove protective masks to pray.

The 30 South Koreans who tested positive for the virus before the church outbreak had either traveled to mainland China or been in contact with someone who had.

However, after Patient 31 attended those religious services, the number of new coronavirus cases per day started to rise. Between February 20 and 29, the number of new cases per day in South Korea spiked from 53 to 909.

While the WHO does not define what a "super-spreader" is, experts say it's someone who is more likely to infect others than a typical infected person. According to a 2011 study, a small percentage of a population — 20% — is responsible for 80% of disease transmission during an outbreak. Those are your super-spreaders.

But the label doesn't necessarily indicate that a given person is more contagious than others, or shedding more viral particles; rather, they have access to a greater number of people in spaces that facilitate infection.

"During the last two decades, super-spreaders have started a number of measles outbreaks in the US," Elizabeth McGraw, an infectious disease expert from Pennsylvania State University wrote in The Conversation. "Sick, unvaccinated individuals visited densely crowded places like schools, hospitals, airplanes and theme parks where they infected many others."

A Westchester super-spreader event boosted New York's outbreak

Research shows time and again that the risk of coronavirus spread is much higher indoors, in poorly ventilated spaces in which lots of people have sustained contact. That's because it primarily spreads via droplets that fly through the air when an infected person coughs, sneezes, or speaks.

A preliminary report from Japanese scientists (which has yet to be peer-reviewed) suggested that the odds an infected person "transmitted COVID-19 in a closed environment was 18.7 times greater compared to an open-air environment." Another pre-print study examined 318 outbreaks in China that involved three or more cases, and found that all but one involved the virus jumping between people indoors.

"The general principle should be: Outside is better than inside; open is better than closed; fewer is better than more people; and stay away from sick people," Dr. Erich Anderer, a neurosurgeon and founding member of the North Brooklyn Runners group, previously told Insider.

That's what makes religious services dangerous.

The story of Lawrence Garbuz, a 50-year-old attorney from Westchester County, New York, underscores that point.

On February 27, Garbuz was hospitalized with pneumonialike symptoms. He had not traveled to China and didn't knowingly interact with anyone who was infected with the coronavirus, but he tested positive for the virus.

A week after his diagnosis, New York state had confirmed 170 cases, including Garbuz's wife and two children. A majority of of them were linked to him, including the neighbor who drove Garbuz to the hospital, the rabbi from his local synagogue, and many other congregants with whom he had interacted during a bat mitzvah and a birthday party on February 23.

Public-health officials created a "containment area" around Garbuz' synagogue in New Rochelle to contain the spread of the virus. Residents were allowed to go in and out, but large gatherings were banned.

A funeral and a birthday party in Chicago led to 13 illnesses and 3 deaths

A case study published in April by the Centers for Disease Control and Prevention described a Chicago super-spreader, known as Patient A1.1, who went to a potluck dinner in February.

The three-person dinner occurred before social-distancing measures were announced; the attendees gathered to eat before attending a funeral. Within a week, both hosts of the dinner and one funeral attendee tested positive for the coronavirus.

Then Patient A1.1, who was experiencing mild symptoms at the time, attended a birthday party, sickening seven others. A week later, three of those infected partygoers went to church, and infected more Chicagoans.

All told, three people who Patient A1.1 came in contact with died, another 13 got sick from coronavirus. According to the CDC, this cluster shows how "extended family gatherings (a birthday party, funeral, and church attendance), might have facilitated transmission of SARS-CoV-2 beyond household contacts into the broader community."

Three other events underscore the role similar gatherings play in the coronavirus' spread:

• In Westport, Connecticut, at least 40 people gathered on March 5 for a birthday party. A week later, half of them were infected; many went from the party to New York City, other parts of the state, and even as far as Johannesburg, South Africa, presumably spreading the virus along the way.
• On May 5, the Walla Walla Union-Bulletin reported that at least 25 residents of the Washington county had been infected with COVID-19 or were under supervision after attending a local party.
• Last week, California health officials revealed that a Pasadena woman who attended a party without a face mask on March 20 (after the state had locked down) passed the virus to at least five other people, CNN reported.

A choir practice became an infection hotspot, too

A choir practice in Skagit County, Washington, was also a super-spreader event, according to a CDC report published Tuesday. During a 2.5-hour rehearsal on March 10, singers sat 6 to 10 inches apart, shared snacks, and stacked chairs together at the end of practice. One of them, it later turned out, had COVID-19.

Of the 61 attendees, 87% were infected; three were hospitalized, and two died.

According to the CDC, super-spreader events like this indicate that the coronavirus "might be highly transmissible in certain settings, including group singing events."

Singing and projecting your voice might be particularly risky activities, since that can send droplets farther than the recommended 6 feet of social distancing.

"These droplets can be pushed farther out, sometimes even beyond 6 feet, if you give the exhalation more energy, with a cough or a sneeze or even singing," William Schaffner, a professor of infectious diseases at Vanderbilt University, previously told Business Insider.

"At this juncture, we don't want people doing voice lessons, even standing 8.5 feet apart," he added.

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