What Have We Learned About COVID-19 From Case Clusters?

by Kroger Health Staff

Last Updated: July 24, 2020

As the U.S. begins to open back up, family parties, a crowded bar, a daycare center in North Carolina, a drive-in graduation in New York, and a meat processing plant in South Dakota are all considered case clusters. But just what is a case cluster, and what can we learn from them to help contain the spread of COVID-19?

A case cluster is a location or event where multiple people contract COVID-19 infections. A cluster can be a workplace, a destination, a social event, or an institution.

Contact tracing is a critical component of identifying clusters. It is a process in which health staffers interview patients who have tested positive for COVID-19 to find out who they’ve been in contact with and where they’ve been, with the goal of discovering who else could potentially be infected.

As contact tracing increases, more individual cases are linked to a cluster, and some clusters may be linked to each other. Public health officials are particularly concerned about clusters because it isn’t only the people who attended an event who are at risk of infection. Infected people may spread the virus to grandparents or other vulnerable family members too.

Some patients are more contagious than others.
Contract tracing provides some insight into the spread of COVID-19. It appears some COVID-19 patients are highly contagious, while others don’t seem to spread the virus at all. On average, most COVID-19 patients infect three other people, but studies and public health officials are identifying so-called “superspreaders” who infect many more. A new study that is in preprint analyzed 9,500 COVID-19 cases and estimated just two percent of people were responsible for 20 percent of transmission.

Loud talkers and singers may increase the spread.
Clusters also suggest some patients’ personal characteristics may play a role. COVID-19 appears to transmit mostly through droplets, although it does occasionally spread through finer aerosols that can stay suspended in the air, enabling one person to infect many others at once. A study of healthy people showed some people disperse more particles when they talk, especially if they are a loud talker. Another study found singing may also release more virus particles than talking. The Centers for Disease Control and Prevention (CDC) issued a report about a case cluster linked back to a choir practice in Washington state in mid-May. One of the attendees reported symptoms similar to a cold, but days later was diagnosed with COVID-19. In the days that followed, 53 other choir members were infected with the virus, and two died.

COVID-19 impacts all ages.
Early in the pandemic, most clusters were centered around nursing homes, affecting mostly older, vulnerable Americans. Data from mid-March found that half of COVID-19 patients were 55 or older. Now that reopening is underway in most states, suspected clusters are tied to bars and parties where younger people socialize and might not be wearing masks. In June, statistics from the CDC showed nearly 70% of positive COVID tests were from patients younger than 60.

Research on the risk factors for COVID-19 is still underway. Until more is known, the best way to protect yourself is to avoid exposure to the virus. The CDC recommends washing your hands often, covering your nose and mouth when around others, and practicing social distancing.

Disclaimer: The information in this story is accurate as of its publication. However, the situation surrounding COVID-19 is ever-evolving. We are working to keep our stories up-to-date as changes occur, but we also encourage everyone to check news and recommendations from the CDC, WHO, and their local authorities.