Last March 29, as states relaxed masking and distancing rules and new COVID-19 infections began to rise, Rochelle Walensky, director of the Centers for Disease Control and Prevention (CDC), issued an emotional appeal for continued caution. At a press briefing, she confessed to a sense of "impending doom" if Americans moved too quickly to resume prepandemic business and social interactions. Other commentators decried the patchwork of safety measures adopted by individual states, including inconsistent mask rules, that left the United States vulnerable to continuing viral spread.

An outbreak of COVID-19 linked to a Chicago exercise facility in August 2020 that infected 55 of 81 people (68%) participating in exercise classes illustrates the vulnerability created by patchwork or inconsistent infection control measures.

The Chicago Department of Public Health investigated the outbreak, finding that while the exercise facility operated at reduced capacity and required masks, temperature checks, and symptom screenings upon arrival, clients were not required to wear masks during classes and most did not. The more infrequent the mask use among individuals, the greater the chances of contracting COVID-19. Among the 58 people participating in exercise class who provided information to investigators, 44 (76%) reported infrequent mask use, including 32 of 38 (84%) who contracted COVID-19 and 12 of 20 (60%) who didn't.

The report on the Chicago health department investigation, published in the CDC's March 5 Mortality and Morbidity Weekly Report, noted that "the increased respiratory exertion that occurs in the enclosed spaces of indoor exercise facilities facilitates transmission" of the COVID-19 virus. Thus, in addition to mask wearing, proper indoor infection control should include improved ventilation, limited class size, enforced physical distancing of six feet or more, increased opportunities for hand hygiene, and consistent reminders to staff and clients to self-quarantine following exposure or a positive test result (several of those interviewed by the researchers admitted to participating in classes after testing positive or having symptoms). Even better, noted the researchers, would be to conduct exercise classes outdoors, where transmission risk is lowest, or virtually.-Frank Brodhead