From the CDC, more on the Breathing vs. Touching debate:
Sukbin Jang, Si Hyun Han, and Ji-Young Rhee
Author affiliations: Dankook University Hospital, Dankook University College of Medicine, Cheonan, South Korea
During 24 days in Cheonan, South Korea, 112 persons were infected with severe acute respiratory syndrome coronavirus 2 associated with fitness dance classes at 12 sports facilities.
… We interviewed consecutive confirmed cases and found all had participated in a fitness dance class. We traced contacts back to a nationwide fitness dance instructor workshop that was held on February 15 in Cheonan.
This was a training session for Zumba instructors. South Korean ladies have gotten into doing aerobics to Latin American rhythms:
Fitness dance classes set to Latin rhythms have gained popularity in South Korea because of the high aerobic intensity (2). At the February 15 workshop, instructors trained intensely for 4 hours. Among 27 instructors who participated in the workshop, 8 had positive real-time reverse transcription PCR (RT-PCR) results for severe acute respiratory syndrome coronavirus 2, which causes COVID-19; 6 were from Cheonan and 1 was from Daegu, which had the most reported COVID-19 cases in South Korea. All were asymptomatic on the day of the workshop. …
By March 9, we identified 112 COVID-19 cases associated with fitness dance classes in 12 different sports facilities in Cheonan (Figure). All cases were confirmed by RT-PCR; 82 (73.2%) were symptomatic and 30 (26.8%) were asymptomatic at the time of laboratory confirmation. Instructors with very mild symptoms, such as coughs, taught classes for ≈1 week after attending the workshop (Appendix). The instructors and students met only during classes, which lasted for 50 minutes 2 times per week, and did not have contact outside of class. On average, students developed symptoms 3.5 days after participating in a fitness dance class (3). Most (50.9%) cases were the result of transmission from instructors to fitness class participants; 38 cases (33.9%) were in-family transmission from instructors and students; and 17 cases (15.2%) were from transmission during meetings with coworkers or acquaintances.
Among 54 fitness class students with confirmed COVID-19, the median age was 42, all were women, and 10 (18.5%) had preexisting medical conditions (Appendix Table 1). The most common symptom at the time of admission for isolation was cough in 44.4% (24/54) of cases; 17 (31.5%) case-patients had pneumonia. The median time to discharge or end of isolation was 27.6 (range 13–66) days after symptom onset.
Before sports facilities were closed, a total of 217 students were exposed in 12 facilities, an attack rate of 26.3% (95% CI 20.9%–32.5%) (Appendix Table 2). Including family and coworkers, transmissions from the instructors accounted for 63 cases (Appendix Figure 2). We followed up on 830 close contacts of fitness instructors and students and identified 34 cases of COVID-19, translating to a secondary attack rate of 4.10% (95% CI 2.95%–5.67%). We identified 418 close contacts of 34 tertiary transmissions before the quarantine and confirmed 10 quaternary cases from the tertiary cases, translating to a tertiary attack rate of 2.39% (95% CI 1.30%–4.35%). …
Characteristics that might have led to transmission from the instructors in Cheonan include large class sizes, small spaces, and intensity of the workouts. The moist, warm atmosphere in a sports facility coupled with turbulent air flow generated by intense physical exercise can cause more dense transmission of isolated droplets (6,7). Classes from which secondary COVID-19 cases were identified included 5–22 students in a room ≈60 m2 [650 square feet or, say 30′ x 22′] during 50 minutes of intense exercise. We did not identify cases among classes with <5 participants in the same space. Of note, instructor C taught Pilates and yoga for classes of 7–8 students in the same facility at the same time as instructor B (Figure; Appendix Table 2), but none of her students tested positive for the virus. We hypothesize that the lower intensity of Pilates and yoga did not cause the same transmission effects as those of the more intense fitness dance classes.
OK, so, if I am reading this right, 26% of students who took one or two 50 minute salsa aerobic classes with infected instructors got infected. Nobody got infected in classes with fewer than 5 students in a 650 square foot room, although that could be a small sample size problem.
But students in Pilates and yoga classes held in the same room at other times didn’t pick up the virus either from an instructor or from touching things. In both Pilates and yoga, you put your hands on the floor, but apparently nobody got infected from germs left on the floor by the salsa aerobics classes. (But perhaps the gym sprayed down the mats or something?)
The implications appear to be that high intensity indoor aerobics are quite risky due to heavy breathing, but less so less intense aerobic workouts. Nor is there all that much evidence from this of transmission by touching things in gyms, such as floor mats.
Perhaps high intensity aerobic workout classes should remain online for the time being, while lower intensity aerobic workouts and anaerobics like weightlifting can be moved outdoors. As I’ve been suggesting for a long time, let storefront businesses temporarily colonize their parking lot spaces in front of their stores.