Study: Late-quarantine students spread coronavirus

Many high school students on day nine or later of their COVID-19 quarantine period tested positive for the virus, a University of Florida study published in JAMA has found. The finding suggests schools should adopt a policy of testing quarantined students if they return to class before the end of the standard 14-day quarantine period in order to limit COVID-19 transmission in schools.

In the study, the UF team found more than 8 percent of high school students who were quarantined as a close contact of a person infected with COVID-19 (within 6 feet for 15 total minutes) tested positive for the virus on days 9 to 14 of quarantine.

“The study underscores the importance of testing,” said Dr. Sarah McKune, Ph.D., one of the study’s authors and a research assistant professor at the UF College of Public Health and Health Professions. “If you do no testing and send kids back between days 10 to 14 of quarantine, a substantial portion of high school kids will go back to school infected.”

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The Centers for Disease Control and Prevention currently recommends a 14-day quarantine period for close contacts of COVID-19 cases, but in December released guidelines for local public health authorities to shorten quarantines. Options include ending quarantine after Day 10 without testing if no symptoms have been reported, or ending quarantine after Day 7 if a diagnostic test is negative and no symptoms are reported.

“Our findings indicate that this is probably not a good practice for high school students,” McKune said.

The UF team evaluated COVID-19 test results among students in Alachua County. The Florida Department of Health in Alachua County conducted testing, contact tracing and follow-up as part of its COVID-19 surveillance in schools.

At the start of the fall semester, the county implemented a policy of quarantining students who were contacts of confirmed COVID-19 cases and offering testing at Day 3 and at Day 9 of quarantine, which was sometimes delayed to days 10 to 14, according to student scheduling and how the days fell around weekends. Students without symptoms who tested negative on days 9 to 14 could return to school on the day following their negative tests. If no test was administered, a 14-day quarantine was required.

Between Aug. 1 and Nov. 30, 2020, 2,189 students at the county’s 49 public and charter K-12 schools were quarantined as close contacts of confirmed cases. Of those, 134 students were tested on Day 3 and 839 students were tested on days 9 to 14. Among high school students, 8.2 percent tested positive for COVID-19 on days 9 to 14, compared with 1.8 percent of elementary and middle school students on days 9 to 14 of quarantine.

The age difference in late-stage quarantine positivity rates may be caused by both biological and behavioral differences between high school students and younger students, the researchers said. Scientists are increasingly finding teens are clinically similar to adults when it comes to COVID-19 infection.

“In addition, high school students have behaviors that increase their risk of infection in general,” McKune said. “They are more likely to be involved in extracurricular activities, including sports, which is where many of these contacts are occurring. They are also more likely to break social distancing norms and engage in close social contact with friends.”

Testing all students before return from quarantine may not be possible in some school systems because of the expense, the researchers said, so following the CDC’s recommendation for a full 14-day quarantine may be a good option, particularly for high school students.

“As more data are available, there needs to be consideration that high school students may need to fall under different policy guidelines than elementary school students,” McKune said. “It is unclear how a rise in SARS-CoV-2 variants will impact guidance moving forward, but our team continues to monitor the data in case changes need to be made.”

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