But while staff were required to wear cloth masks, the camp did not ask campers to do so, and did not open windows and doors to increase air circulation in buildings. The campers stayed overnight in cabins, with an average of 15 occupants in each.
Many camp activities — which took place indoors as well as outdoors — included “vigorous singing and cheering,” which can enhance spread of the virus, the report said.
The case highlights the limitations of asking for proof of negative coronavirus tests before large gatherings, Dr. Malani said.
“Testing doesn’t always mean safety,” she added. “It has to be combined with individuals adhering to strict quarantine. And that’s hard to do for young people, on a college campus, and in K through 12.”
Inconsistent mask wearing is also problematic, she said.
“Even if the staff were wearing masks around the campers, it’s likely that when they were back in their quarters at night, they weren’t — because that’s what happens,” Dr. Malani said. “It’s hard to do, because it’s not natural to have to distance all the time and wear a mask.”
In a recent study of an outbreak at a high school in Jerusalem that began 10 days after in-person classes resumed in late May, 13 percent of the student body and 16 percent of the staff ultimately tested positive.
Though the students were supposed to wear face masks and practice social distancing, researchers concluded crowded classrooms of up to 38 students made distancing impossible. Air conditioning may have accelerated the spread of the virus.