1. In a group of 13 school districts in North Carolina where school activities were held in-person with several mitigation strategies in place, in-school transmission of COVID-19 was low, with an attack rate <1%.
2. 75% of cases acquired in high schools were associated with school-sponsored sports.
Evidence Rating Level: 2 (Good)
Study Rundown: Nearly all U.S. schools closed for in-person education early in the COVID-19 pandemic. As numbers of SARS-CoV-2 infections have risen and fallen in the United States, decisions about school reopening at state and district levels have often taken community infection rates into account. This study tracked school-acquired infection rates in 13 North Carolina districts with more than 100,000 students and staff between October 2020 and February 2021 to determine whether surging COVID-19 cases in the community led to increased in-school infections. All schools used a hybrid model of in-person and virtual learning, and engaged in various mitigation strategies to prevent spread amongst students. Overall, while community cases surged, there was minimal in-school transmission; 209 school-acquired infections were recorded in the study period among 26,000 close contacts, which represented an attack rate of < 1%. 75% of high school cases were transmitted during athletic activities. The specific measures implemented in these districts, particularly the regular input of public health officials, may not be realistically reproducible in all U.S. schools. Without centralized testing or surveillance testing, this study also speaks only to the role of symptomatic cases. Overall, this study shows that school openings need not be contingent upon low community-spread, and that with appropriate mitigation strategies, in-school transmission of COVID-19 is low.
In-Depth [prospective cohort]: The 13 school districts included in this study voluntarily submitted weekly data on numbers of molecular test-confirmed COVID-19 cases and on contact tracers’ determinations of community versus in-school transmission. The districts had wide variation in the racial, ethnic, and socioeconomic makeup of their student populations. The schools used a hybrid model in which up to 50% of students attended school each day, and all districts allowed in-person extracurricular activities including sports. Schools implemented universal masking, hand-washing, and 6-foot distancing in middle and high schools, although distancing was not enforced for elementary school students. The districts did not install new ventilation systems or air filters. Cases were defined based on positive molecular diagnostic tests; contact tracing was then used at a district or county level to determine whether each case was school or community-acquired. Districts issued guidelines on when students and staff should be tested, but did not provide surveillance testing or in-school testing. During the 4-month study period, 4,969 community-acquired infections were recorded in the school districts. The 209 school-acquired infections occurred due to more than 26,000 close contacts between infected students and staff with others, yielding a secondary attack rate of <1%. An interrupted time-series analysis was used to compare rates of in-school infection between the study period and a previous period (August to October 2020), yielding a relative rate of 2.3 (95% confidence interval 1.2-4.7).
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