Weekly COVID-19 testing of asymptomatic students and staff at three K-12 public schools in Omaha, Nebraska, roughly doubled the detection rate of symptom-based testing and exceeded that of the rest of the local county, according to a study yesterday in JAMA Network Open.
The pilot quality-improvement project, led by University of Nebraska Medical Center scientists and the Omaha Public School District, involved weekly self-collected saliva testing and twice-weekly sampling of school wastewater and air and surfaces of high-risk areas from Nov 9 to Dec 11, 2020.
At that time, all district schools offered hybrid instruction, alternating cohorts for distance and in-person instruction; 50% to 60% of students chose in-person learning. Routine staff COVID-19 testing was mandatory, while it was optional for students.
Interrelated school, community risk factors
Over the study period, the team tested 2,885 saliva samples from 458 employees and 315 students. Routine testing detected 22 SARS-CoV-2 infections in students and 24 in staff members, representing a 1.2% to 7.0% higher case detection rate among students and a 2.1% to 5.3% increase among staff, relative to symptomatic testing.
"Compared with conventional reporting in our setting (passive case finding), our results suggest that as many as 9 in 10 student COVID-19 cases and 7 in 10 staff COVID-19 cases may have been missed by conventional reporting mechanisms," the study authors wrote.
A geographic analyses of coronavirus cases districtwide showed higher community risk in ZIP codes closest to the pilot schools. "The differences between the pilot program case rates and observed community case rates indicate that [such pilot programs] may assist in mitigating school-based transmission risk through informing case isolation, contact tracing, and management of school activities and may serve as a trigger to escalate community-based surveillance, particularly among school-aged children," they wrote.
Most COVID-19 cases among staff were identified within 1 week of their last negative test result, while half of the student infections were detected 2 or 3 weeks later, indicating more inconsistent student participation, the researchers said.
Staff were, on average, 42.9 years old, 66.2% were women, 68.1% were White, 18.1% were Hispanic, 5.5% were Black, and 7.6% were of other or unknown race. Students, on average, were 14.2 years old, 48.0% were girls, 63.8% were Hispanic, 23.8% were White, 6.3% were Black, and 6.0% were of other or unknown race.
Possible role for environmental monitoring
Whole-genome sequencing of saliva samples from 21 coronavirus-infected participants and wastewater sampling from all schools and air samples from two choir rooms detected SARS-CoV-2 RNA (not live virus) in 3.3% of 60 air samples and 1.7% of 60 surface samples. There were two infection clusters consisting of two employees and two students at one school.
While the researchers noted that wastewater samples over 2 weeks at one school tested negative for SARS-CoV-2 despite positive saliva test results, "the use of wastewater autosampling instruments for the collection of time-distributed composite wastewater samples may increase sensitivity for case detection and will be further explored," they wrote.
The cost of wastewater sampling was roughly $750 per week per school, or 75 cents per person, for a school of 1,000 students and staff members, relative to $10 to $50 per person for testing individual or pooled samples.
"Thus, wastewater and other environmental monitoring may ultimately provide cost-effective, building-level surveillance to identify SARS-CoV-2 transmission hotspots and prioritize more resource-intensive individual screening, a strategy that has been successfully pursued in university housing and nursing home settings," the researchers said.