What Turns A Gathering Into A Super-Spreader Event?

Understanding why some get-togethers become super-spreading events is going to be critical in the continued fight against coronavirus, as a growing body of research seems to confirm that a relatively small group of people tend to be responsible for a huge number of cases.

For example, in a preprint of a study that became available last week, researchers analyzed cases in Georgia and found that 20% of all infections were caused by just 2% of people with COVID-19. Other earlier research of coronavirus clusters in Hong Kong indicated that about 20% of cases were responsible for a full 80% of infections.

What specifically puts a gathering at risk for becoming a super-spreading event is less clear. Preliminary data seems to indicate that the racial justice protests that are being held country-wide cannot be linked to the current huge spike in cases, for instance. Researchers have pointed to a few possible reasons for that: Rally-goers may be wearing masks, or self-quarantining after attending a protest; they may tend to be younger in age, and therefore less likely to develop severe symptoms. It’s being reported that outdoor activities are not a high-risk form of transmission, as well. 

Other events, however, have been directly linked to dozens of transmissions. There was the biotech conference in Boston in February that infected nearly 100 attendees. A funeral in Georgia resulted in over 100 people testing positive for COVID-19. Then there was the person who infected 52 others at choir practice, two of whom died. A birthday party in Texas left 18 people with COVID-19. What was it about these gatherings that made them breeding grounds for the coronavirus?

While more research is needed before experts can say for sure which events are most likely to become super-spreaders, a few different factors appear to be important.

“An event held indoors with larger group sizes, louder talking (such as over music) or heavy breathing (such as exercise), and for longer duration are all factors that increase the likelihood of super-spreading from attendees who have the virus but no symptoms,” says Sachin Nagrani, MD, the medical director of Heal, a telehealth and house call app. Most of the super-spreader events identified earlier had many of these very things in common.

Talking, shouting, singing, and heavy breathing all cause people to expel respiratory droplets, which we know are the main way coronavirus is passed along — particularly if people aren’t wearing face masks, one easy and proven way to reduce transmission. Indoors, there's “less ventilation, limited sunlight sanitizing surfaces, and typically less space to distance from others,” Dr. Nagrani tells Refinery29. As a result, those droplets can hang around, infecting a maximum number of people.

"Large indoor events with no masks or distancing could result in massive amounts of transmission as compared to smaller, outdoor events where people cover their faces and stay away from each other," confirms Ben Althouse, Ph.D., a research scientist at the Institute for Disease Modeling in Bellevue, WA. He tells Refinery29 that whether or not the attendees of the get-together are susceptible to infection also plays a role.

“In a study of 110 case-patients from 11 clusters in Japan, all clusters were associated with closed environments, including fitness centres, shared eating environments, and hospitals; the odds for transmission from a primary case-patient were 18.7 times higher than in open-air environments,” the Centers for Disease Control and Prevention states.  

The timing of the event may matter too. A great deal of transmission seems to occur in the window of time after a person is infected but before they are symptomatic, according to a study in the journal Nature Medicine. A person attending an event within that period may create a super-spreading situation, whereas if they had attended just a few days before, they wouldn’t have. It's also possible that people with a higher viral load — which means they have more virus in their droplets than others — could make a person more likely to become a super-spreader, reports CNN. 

The bottom line is, we’re not out of the woods yet. In many states, case counts are rising alarmingly quickly. On Tuesday June 30, Anthony S. Fauci, MD, said there’s a risk that the U.S. could reach 100,000 cases a day if something doesn’t change. “I’m not satisfied with what’s going on because we’re going in the wrong direction,” Dr. Fauci, the director of the National Institute of Allergy and Infectious Diseases, said, according to The Washington Post. That day, the U.S. recorded more than 48,000 additional cases.

“Coronavirus cases are surging in many areas of the country right now, so unfortunately the responsible choice is to avoid many events we may desire attending,” Dr. Nagrani says. “Indoor or combined indoor-outdoor gatherings, outdoor gatherings of more than 10 people, or any type of gathering in areas where the virus is increasing in activity should be avoided right now.” 

If you’re going to go to a small outdoor get-together, and the place you live is allowing it, “wear a mask, maintain six feet of distance from others, limit touching surfaces, and use hand sanitizer if you contact any common surface,” Dr. Nagrani advises. "If you or your family exhibit any symptoms of COVID (fever, cough, muscle pain, loss of smell) do not attend the event and call your primary healthcare provider for advice," adds Althouse.

We know: We’ve been stuck inside for months, and we all want to start getting back to normal. But if we don’t stay the course now, we’ll only be setting ourselves back. So skip the party in favour of an intimate, social distancing picnic or a solo Netflix marathon instead. It’s the right, socially responsible thing to do. And if you do leave your home? Wear a face mask!