Jan. 26 (UPI) -- COVID-19 transmission in schools is nearly 40% lower than spread in surrounding communities, thanks to high compliance with mask-wearing protocols among students and teachers, according to data released Tuesday by the U.S. Centers for Disease Control and Prevention.
There were 191 cases of the new coronavirus among 5,530 students, teachers and administrators in 17 elementary, middle and high schools in Wood County, Wis., between Aug. 31 and Nov. 29 of last year.
Fewer than 4% of these cases were associated with in-school transmission, and all of the cases involved students, according to the CDC.
This equates to an infection rate of 3,453 cases per 100,000, the data showed, compared to a rate of 5,466 cases per 100,000 people in the surrounding communities of the county.
"Despite widespread community transmission, COVID-19 incidence in schools conducting in-person instruction was 37% lower than that in the surrounding community," CDC researchers wrote.
"The absence of identified child-to-staff member transmission during the 13-week study period suggests in-school spread was uncommon, [although] this study was unable to rule out asymptomatic transmission within the school setting because surveillance testing was not conducted," they said.
Wood County encompasses a rural area in central Wisconsin with a population of just under 75,000 people, according to U.S. census figures.
The county's 17 schools opened in August "under district and statewide mask mandates," and were found to have "high teacher-reported student masking compliance," the CDC said.
More than 92% of students, teachers and administrators in the schools complied with regulations calling for the wearing of face coverings to prevent the spread of COVID-19.
In addition, a little over 12% of the students in the 17 schools attended classes virtually, meaning they were not directly exposed to their fellow students and others at school facilities.
Mask wearing among those in the surrounding communities was not assessed as part of the research released Tuesday.
High levels of masking compliance, small groups of students -- with a maximum of 20 students -- and limited contact between those groups "likely helped mitigate in-school [COVID-19] transmission and could be responsible for the low levels of transmission detected in schools," the agency researchers wrote.
"Investigation of 191 school-related COVID-19 cases in students and staff members suggested that most transmission occurred outside of required school activities," they said.