Study population and setting
This study investigated a suspected COVID-19 outbreak first identified on July 2, 2020 by the Hawaii Department of Health. Fitness Instructor A tested positive by RT-PCR, and displayed signs and symptoms. Instructor A taught at two facilities (X and Y), and was linked to 21 cases. Another instructor, B, came into contact with Instructor A and later tested positive. Instructor A taught a class on June 27 at Facility X (60 hours before symptom onset), and another class on June 28, 38 hours before symptom onset at Facility Y. While Instructor A followed social distancing and sanitization protocols, they shouted instructions at students without a mask at a distance >6 ft. They taught another class on June 29 at Facility Y, 4 hours before symptom onset. A number of students had exposure to Instructor A during multiple classes. Instructor B worked at a third facility, Z, and was exposed via the June 28 class at Facility Y. Instructor B taught five personal training sessions and small-group classes at Facility Z 2 days after their first exposure, and more than 2 days before their symptom onset. They taught another person on July 1, and another 10 participants and 3 small classes on July 2, before developing symptoms 12 hours later.
Summary of Main Findings
The study calculated the attack rate for each class, ranging from 0% to 100%. The highest attack rate (10/10, 100%) was seen at Facility Y during a stationary cycling class with Instructor A where no one was masked on June 29. All participants tested positive by RT-PCR. For Instructor B at Facility Z, the highest attack rate was seen at the kickboxing small group class on July 2, 12 hours before symptom onset, where only 2 participants of 9 who attended were masked, and all (9/9, 100%) later tested positive by RT-PCR. There was a notable gradient of attack rates based on proximity to symptom onset for both instructors. Instructor A had an attack rate of 0% for classes taught >1 day from symptom onset, but 100% attack rate for <1 day. For Instructor B, more than 2 days from onset had an attack rate of 0% for 33 participants in the classes, and 13% attack rate for <2 and >1 day from symptom onset. Finally, <1 day from symptoms, Instructor B had a 95% attack rate in classes.
The study strength was the depth of data collected for the type of classes, whether individuals were masked, and the timing of classes taught. This investigation allowed them to calculate attack rates for each class, as well as based on symptom onset. They also investigated the COVID-19 distancing and sanitation protocols in place, and whether they were being adhered to.
The study notes that participants may have multiple dates of exposure, and so it may be challenging to uncover exactly when transmission could have occurred for some. Additionally, they did not require all contacts be tested, and so some individuals who did not experience symptoms or who refused testing were assumed to not have COVID-19 when calculating the attack rate. Thus, these estimates may underestimate the level of transmission among these classes.
This study shows the high risk of transmissibility of COVID-19 in exercise settings despite other COVID-19 mitigation protocols being followed and demonstrated that transmission in this setting was likely highest in the day of or before symptom onset of the infectious case.
This review was posted on: 12 March 2021