SARS-CoV-2 spread rapidly at Wisconsin summer camp; 76% infected
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After a student at an overnight retreat in Wisconsin began exhibiting symptoms of SARS-CoV-2 infection this summer, the virus spread rapidly, infecting more than three-quarters of attendees, researchers said.
The student tested negative for COVID-19 via PCR less than a week before attending the retreat, they added.
The retreat included 152 high school-aged boys — aged 14 to 24 years — and counselors and staff members from 21 states and territories and two foreign countries. All attendees were required to provide documentation of either a positive serologic test result in the last 3 months or a negative reverse transcriptase (RT) PCR test within the last 7 days before travel. Everyone was also required to wear a mask during travel.
Ian W. Pray, PhD, MPH, an epidemic intelligence service officer at the CDC, and colleagues reported that during July 2 to August 11, 116 (76%) attendees had COVID-19 — 78 confirmed (51%) and 38 probable (25%). Of the 38 attendees with probable COVID-19, 34 received negative RT-PCR results on specimens received 11 to 22 days after presenting symptoms.
“The large number of symptomatic individuals early in the outbreak overwhelmed the camp's ability to track, isolate, and quarantine sick and exposed attendees,” Pray told Healio. “We mentioned in the report that earlier engagement with public health authorities to discuss recommended mitigation strategies might have aided prevention and control efforts, and ‘cohorting’ campers (limiting the size of groups) might have helped reduce the number of infections.”
The Wisconsin Department of Health Services (WDHS) was notified about the spread and began an investigation. WDHS instructed retreat organizers on mitigation strategies like symptom monitoring, isolation of symptomatic attendees and quarantine of contacts, but the large volume of symptomatic attendees far exceeded the capacity for such measures.
“The student was isolated as soon as the positive test was received, but unfortunately other campers had been exposed and the outbreak was not contained,” Pray said. “We would recommend that campers are isolated as soon as they develop symptoms, which may have helped if done here, but we also know that people with COVID-19 may be infectious 2 or more days before showing symptoms, so this may not have fully contained the outbreak.”
By the end of the retreat, 118 of the 152 (78%) attendees had a positive serologic test result. Twenty-four attendees with a documented positive serologic test before the retreat tested negative on PCR.
“An interesting finding was that all but one [attendee] developed symptoms, which suggests that asymptomatic transmission was less common here than reported elsewhere,” Pray said.