CDC: Maine overnight camps hosted over 1,000 kids and counselors, and only 3 contracted the coronavirus. Here is the safety plan they followed.

• The camps all followed the same plan that included rounds of screening, testing, and quarantining before and after camp arrival.
• Campers and counselors were split into cohorts that quarantined together like family units.
• Three asymptomatic attendees at three different camps tested positive for COVID-19 after arrival, but none of them spread the virus to others at camp.

Four overnight camps in Maine implemented a multi-layered strategy to prevent the spread of the coronavirus, and, in doing so, successfully avoided secondary transmission, according to a report out today from the Centers for Disease Control and Prevention.

The four camps hosted a combined total of 1,022 kids and staffers from across the US and abroad.

Two staff members and one camper at three different camps tested positive for COVID-19, though they showed no symptoms, after arriving at camp. They were quickly isolated and their contacts were quarantined, resulting in no spread to other camp members.

A recent outbreak at a camp in Georgia demonstrated how just one case can spread rapidly without proper containment, as 260 campers and counselors tested positive after one staffer came down with the virus.

While the campers in Georgia were not required to wear masks, campers and counselors in Maine were masked when participating in activities outside of their assigned cohorts, which ranged from five to 44 people depending on the camp.

Employing a multilayered strategy allowed the camps to mitigate the spread of coronavirus

Laura Blaisdell, lead author of the report and a camp mom herself, said there's not one gold-standard strategy that is 100% effective at preventing the spread of coronavirus. She said this intervention was successful because it combined multiple strategies including early identification and isolation, quarantining, cohorting, masking, and physical distancing.

"It's like a piece of Swiss cheese. Every layer has a limitation, and it's the putting of the layers on top of each other that allows us to cover up those holes," Blaisdell said.

Camp attendees were instructed to quarantine at home with their family units for 10-14 days before arrival, then quarantined with their cohorts for 14 days after arrival.

The camps required attendees to show negative coronavirus test results from 5-7 days before arrival, with four attendees delaying their arrival because they tested positive. At one camp, 15 campers were isolated while they waited to learn their test results.

Campers and staffers were tested again a week after arrival, which yielded positive results for three attendees. The positive individuals were isolated until they tested negative, and their cohorts quarantined for 14 days. The camps also implemented daily temperature checks and questioning about COVID-19 symptoms.

The cohort system limited indoor interactions that could lead to transmission

By assigning campers and counselors to small, stable cohorts, the camps cut down on scenarios that could spread the virus and set clear expectations for mask-wearing.

"Those cohorts acted essentially and functionally as family units," Blaisdell said. The groups initially quarantined together, and campers were allowed to not wear a mask while within their cohort.

The cohorts dined together, bunked together, and used the same bathrooms. The camps limited mixed-cohort indoor activities where the virus might spread, and encouraged sports that allowed physical distance between cohorts, according to the CDC report.

Blaisdell said the camps were able to create a "culture of compliance" around mask-wearing within the larger camp community, and they didn't have any issues with people not wearing masks.

"As a public health trained physician, I'm thrilled about the results because we entered into the summer with a small degree of trepidation and a large degree of uncertainty," Blaisdell said. "As a camp mom, I'm equally grateful because my sons were able to play and to connect with friends and to enjoy being outdoors after having a tough spring."