COVID-19 Outbreak Among Attendees of an Exercise Facility — Chicago, Illinois, August–September 2020

Investigation and Results

During August 24–September 1, 2020, an exercise facility offered four to eight high-intensity indoor classes daily. All classes were held at ≤25% capacity (i.e., 10–15 persons). Mask use, temperature checks, and symptom screenings were required on entry; however, patrons were allowed to remove masks during exercise. Patrons brought their own mats and weights and were stationed ≥6 ft apart. On September 1, a patron notified the facility of receipt of a positive test result. The dates of symptom onset and last exercise class attendance were both August 28. The facility closed for 13 days and informed all attendees of their possible COVID-19 exposure. On September 8, during routine case investigation, CDPH identified a cluster of cases linked to the facility. When CDPH first contacted the facility on September 10, the facility had already notified all attendees (employees and patrons) of potential COVID-19 exposure and learned of 41 patrons with COVID-19–compatible symptoms or positive test results. The facility provided contact information and last attendance date for all persons who had attended classes during August 24–September 1.

Case investigations were conducted using standardized REDCap data collection tools (version 10.3.3; Vanderbilt University). All August 24–September 1 class attendees were contacted for interview during September 14–22. Testing and outcomes data,^† social activities,^§ and in-class behaviors (i.e., mask use and physical distancing) were assessed.

A laboratory-confirmed case was defined as a positive SARS-CoV-2 RT-PCR test result for any facility attendee during August 24–September 15. Attendees with symptoms clinically compatible with COVID-19^¶ who did not have a positive test result were considered to have probable COVID-19. Self-reported positive test results were confirmed through Illinois’ National Electronic Disease Surveillance System (I-NEDSS). Characteristics of attendees with and without COVID-19 were compared using Fisher’s exact test. Associations between in-class behaviors and COVID-19 case status were estimated using logistic regression.** The primary analyses included probable and confirmed cases. A complete-case sensitivity analysis included only attendees with laboratory-confirmed positive or negative COVID-19 status (i.e., a positive or negative SARS-CoV-2 test result) who also provided information on frequency of in-class mask use and distancing. Analyses were completed using SAS (version 9.4; SAS Institute). This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.^††

Among 91 facility attendees (88 patrons and three employees), 10 had neither testing nor interview data available and were excluded. Among the remaining 81 attendees, 55 (68%) COVID-19 cases were identified, including 49 (60%) laboratory-confirmed cases and six (7%) probable cases; all identified cases were among patrons. Seventy-three (90%) attendees were interviewed, including 47 (85%) of 55 with COVID-19. Eight attendees with laboratory-confirmed COVID-19 (16%) were not interviewed.

Sixty-eight (84%) attendees were Chicago residents, 71 (88%) were women, and 72 (97%) were non-Hispanic Black; the median age was 42 years (interquartile range [IQR] = 29–55 years) (Table 1). Among 73 interviewees, 24 (33%) reported medical conditions associated with severe COVID-19 illness^§§; asthma was the most frequently reported underlying condition, reported by 11 (15%) attendees.

Twenty-two (40%) attendees with COVID-19 reported measured or subjective fever (Table 2). Two (4%) visited an emergency department; one (2%) patient was hospitalized for 8 days. No deaths were reported. Symptom onset dates ranged from August 19 to September 11. Twenty-two (40%) attendees with COVID-19 attended an exercise class on or after the date of symptom onset, including three (5%) who attended on the same day or after they received the positive test result. Overall, 43 (78%) attendees with COVID-19 attended an exercise class during their estimated infectious periods. Attendees with COVID-19 reported participating in a median of five exercise classes (IQR = 3–7); attendees without COVID-19 reported attending a median of three exercise classes (IQR = 1–6).

Two attendees with COVID-19 (attendees A and B) reported symptom onset during August 19–20; each attended five classes during August 24–September 1 while symptomatic (Figure). Attendees A and B both received positive SARS-CoV-2 RT-PCR results after the facility closed; both reported mask use ≤60% of the time in class (infrequent mask use).

Among 58 (72%) interviewees who provided information on in-class behaviors, including 38 (69%) attendees with and 20 (77%) without COVID-19, infrequent mask use during class was reported more commonly among attendees with COVID-19 (32; 84%) than among those who did not have COVID-19 (12; 60%) (odds ratio [OR] = 3.5; 95% confidence interval [CI] = 0.9–15.1). Twelve attendees with COVID-19 and eight who did not have COVID-19 reported social exposures outside the exercise facility during August 19–September 2 (Table 1). Sensitivity analyses included 32 attendees with positive SARS-CoV-2 RT-PCR test results and 10 with negative results (Supplementary Table; https://stacks.cdc.gov/view/cdc/103076). Findings were similar to those of the primary analysis: 28 (88%) attendees with COVID-19 and six (60%) without COVID-19 reported infrequent mask use during an exercise class; the odds of infrequent mask use were greater (OR = 4.5; 95% CI = 0.6–32.2) among attendees with COVID-19 than among those without COVID-19.