Masked students in school (Gundam Ai via Shutterstock)

Contact tracing and genomic sequencing helped Centers for Disease Control scientists track COVID-19 spread from a workplace cluster and household transmission to limited spread in a Connecticut classroom last fall. 

The process was outlined in an early CDC article on a study set to be released in October. All told, the CDC and the state Public Health Department identified 16 intertwined cases stemming from six infections at a workplace. Much of the spread outlined in the study hinges on one worker, identified as W-3, who also worked in a school and a fitness center. The virus moved from W-3 to at least six other people in their household, classroom, or fitness classes.

The spread, particularly the school-based transmission, is of interest as students begin returning to Connecticut classrooms this week amidst a surge of cases driven by the more-transmissible delta variant. 

“Classroom transmission of SARS-CoV-2 is uncommon in the context of prevention strategies such as masking and distancing; previous studies have suggested that most school-associated cases are acquired outside of school,” the CDC conclusion read. “However, our results suggest that staff-to-staff and staff-to-student transmission occurred in this classroom.”

A spokesman for the Public Health Department did not return calls for comment on this story. 

In this case, the spread in the classroom of about 15 students was limited. Two students, who experienced no symptoms, eventually tested positive for the disease. Symptoms did appear in two family members of one of those students. Meanwhile, a substitute teacher who briefly supervised the class also contracted the virus. 

The relatively limited spread in a classroom with more than a dozen people may have been due in part to mitigation efforts. According to the study, both staff members reported strict adherence to public health guidelines including masking and distancing. Classroom windows remained open to improve ventilation.

This year, Gov. Ned Lamont has once again required students and staff to wear masks in schools. Although recommended by the CDC and the American Academy of Pediatrics, the order has been met with outspoken opposition by a group of parents. 

Other elements will impact school transmission this year. Last fall, when the CDC study was conducted, there was no vaccine available to reduce spread of the virus. This year, the governor has mandated school staff be vaccinated. Students are also returning to classrooms this year amidst a surge of the more transmissible delta variant. On Friday, the state infection rate stood at 3.44%.

Meanwhile, the study tracked COVID transmission beyond the classroom. W-3 also taught an indoor class at a local fitness center before experiencing symptoms of the virus. About six people attended the class and two of them felt symptoms in the next five to seven days. A family member of one of the positive attendees later contracted the virus. According to the study, masks were removed during exercise but participants were more than six feet apart during that time. 

“Fitness centers might consider moving high-exertion exercise outdoors, improving ventilation, and promoting mask use during indoor exercise,” the study concluded. State public health orders changed last November to require patrons to wear their masks at all times, even while actively exercising. That order is no longer in effect for vaccinated people. 

Although a cluster of COVID cases appeared at W-3’s initial workplace, the study concluded that it was not due to transmission there. Rather viral sequencing suggested the cases were contracted individually elsewhere. 

“However, workplace transmission from unidentified employees or customers remains possible. In addition, a workplace employee and their household contact had unrelated sequences, suggesting that they also were infected independently,” the authors concluded. “This apparent workplace cluster, disproven by sequencing, highlights challenges in defining transmission chains during widespread SARS-CoV-2 community transmission. These findings highlight the crucial role of genomic sequencing in clarifying transmission chains.”