An Illinois church summer camp and men's conference in June has been linked to 180 confirmed and probable COVID-19 cases, the Centers for Disease Control and Prevention reported Tuesday.
The camp and conference did not require attendees to be vaccinated, tested or masked, the CDC reported, and the high rate of transmission was likely to have been driven by the delta variant of the coronavirus.
The report, published in the Morbidity and Mortality Weekly Report, found that as of Aug. 13, a five-day overnight summer camp and a two-day men's conference, both sponsored by a church, had led to 180 confirmed and probable cases identified by contact tracers.
The Chicago Tribune reported that the camp outbreak occurred at the Crossing Camp in Rushville, in central Illinois, about 70 miles southwest of Peoria.
Calls to the Crossing Camp went unanswered, and it did not immediately respond to an email requesting comment.
Illinois officials first reported the outbreak to the CDC on June 30, the report said.
The June 13-17 summer camp session did not require COVID-19 vaccinations or testing and did not mandate masks, and campers slept in groups of about 100 people in "large, shared boarding facilities."
Campers were in frequent close contact with small groups of staff members and campers for indoor and outdoor activities.
On June 16, a camper left early because "fever and respiratory symptoms" and tested positive for the coronavirus.
Six of the camp staff members who eventually tested positive left camp to attend the men's conference at a different location June 18 and 19. All six tested positive after the conference ended.
The men's conference, like the camp, required no vaccinations, testing or masking.
By Aug. 13, the CDC had found 87 primary cases linked to the summer camp and 35 linked to the men's conference. Through contact tracing, the CDC identified 58 more secondary cases among close contacts of camp or conference attendees.
The study found that the attack rate — which the CDC says is "the risk of getting the disease during a specified period, such as the duration of an outbreak" — was 26% among campers and staffers and 7% among conference attendees.
Of all 180 cases, 29, or 16.1%, occurred in fully vaccinated people, none of whom required hospitalization, the CDC said.
Of the 31 samples that were genetically sequenced, 87% were identified as the delta variant, 10% were identified as the alpha variant, and 3% — one case — was identified as the gamma variant.
The CDC report warned that the 180 cases are likely to be an underestimate because it did not have access to camp rosters and not all people participated in contact tracing. In addition, at-home positive antigen tests were not counted.