How COVID-19 Spread Through a University's Soccer Teams, Chicago, 2020

In August 2020, the Chicago Department of Public Health was told of a cluster of COVID-19 cases on a university's men's and women's soccer teams. Its investigation, reported in CDC's MMWR, traced how the virus moved through a group of students who lived, trained and socialized together — and why precautions at practice weren't enough.

Precautions on campus

The student athletes returned to campus in June. Each needed two negative PCR tests before any preseason training. University policy limited gatherings on campus and required masks everywhere except students' own residences, along with social distancing and daily health screening. Masks were mandatory at training, and coaches reported that everyone complied. Voluntary training sessions for both teams began in July.

How the outbreak unfolded

• In August, a men's team player told coaches about COVID-19 symptoms. In the previous 14 days the player had been to several social gatherings with teammates, including a birthday party and an unofficial coed match between the men's and women's teams.
• Over the next two days, five more players reported symptoms, and both teams were told to isolate or quarantine. Of 10 people tested — symptomatic players and others at the party or the match — 9 were positive.
• Three days later, four more players tested positive. When the university then tested every team member, including those without symptoms, four more infections turned up: 17 in all.

COVID-19 cases among the soccer teams by date of specimen collection, with key events, July–August 2020 (CDC).

What investigators found

All 45 students who trained during the investigation period were interviewed — 21 men's players, 23 women's players and one women's team staff member. Their median age was 20.

• 17 of 45 were infected (an attack rate of 37.8%). Eleven had symptoms; none were hospitalized.
• Besides the coed match, students reported 18 social gatherings during the investigation period: the birthday party, visits to friends' dorm rooms or apartments, and outdoor gatherings at a lake. Most students (60%) said they attended at least one, and seven who said they hadn't were named by teammates as having been there.
• Shared housing was the strongest link. Thirty-three students (73.3%) lived with teammates, and infected students had higher odds of living in shared housing than uninfected ones (odds ratio 10.4).
• Three events likely drove transmission, because members of both teams and outsiders attended them:
• • The birthday party. Seven men's players attended, said they wore masks or distanced less than 10% of the time, and all later tested positive. Teammates knew of two athletes outside the soccer teams who were also diagnosed after the party.
  • A dorm or apartment visit, attended by men's players from the party (M2–M7) and one women's player, who later tested positive.
  • The coed match, a week later, attended by those same students and 21 teammates; five more later tested positive. Only half of the students said they wore masks more than 90% of the time at the match.
• Genome sequencing of 12 specimens from 10 students found closely related viruses, consistent with a single introduction, though the exact chain of transmission couldn't be traced. The viruses belonged to a clade circulating in the Chicago area since March.

The university's response

Students with symptoms were taken out of play, tested and isolated; exposed students were quarantined separately and tested. Players in on-campus dorms were moved to quarantine dorms to keep roommates from infecting each other. Students returned to training after completing isolation or quarantine, and the university began mandatory weekly saliva testing for all athletes, students in campus housing and performing arts students.

Lessons

• Precautions at practice can be undone off the field. Masking and distancing at gatherings were minimal, which quickly erased the benefits of pre-training tests and on-campus rules. Encouraging masks and distancing outside official activities could help.
• Regular testing catches silent spread. Periodic screening could have found nine infected players before they went to four social gatherings.
• Shared housing combined with gatherings where precautions weren't followed may have compounded the risk.

The investigation had limits: some students wouldn't name contacts outside the teams, many struggled to recall dates and event sizes, not every positive specimen could be sequenced, and exposure periods for students without symptoms were estimates.

The authors concluded that colleges need more effective messaging and strategies to promote masks and distancing in social settings, and that periodic repeat testing — of exposed students, of groups caught up in an outbreak, and of students without known exposure — can help detect outbreaks sooner where community transmission is moderate to substantial.

Sources

• Teran RA, Ghinai I, Gretsch S, et al. "COVID-19 Outbreak Among a University's Men's and Women's Soccer Teams — Chicago, Illinois, July–August 2020," MMWR Vol. 69, No. 43, CDC; a work of the United States government in the public domain.