June 27, 2022: UF researchers determined how long children remain infectious with the omicron viral variant after receiving a positive test result for SARS-CoV-2.
Children infected with COVID-19 may need more than the five days of isolation recommended by the Centers for Disease Control before returning to school, new research by University of Florida investigators shows.
The study, published on the preprint server MedRxiv while it awaits publication in a scientific journal, assessed how long children remained infectious after their symptoms began and after an initial positive test result for COVID-19.
The findings raise questions about current guidelines from the CDC and the Florida Department of Health, which both specify a five-day quarantine for children before returning to school. Current guidelines from the CDC also recommend an additional five days of wearing a mask after isolation has ended, while the FDOH outlines no further mask requirements.
The study, spearheaded by researchers at the UF Emerging Pathogens Institute, enrolled 31 children in a two-month period when the omicron viral variant was burning through the state last winter.
The researchers report that 67% of the children were positive for SARS-CoV-2 on day five after their first positive test. And 48% were still positive with a rapid antigen on day seven. Only about 10% were still positive by day 12.
“Our data suggest that close to half of children are still infectious by the seventh day after onset of symptoms, and that they may spread the virus to family, friends, and classmates even after the recommended five-day isolation period,” said the study’s senior author, UF EPI Director J. Glenn Morris, M.D. & M.P.H.
To establish how long a child was still infectious after initial onset of symptoms with a positive COVID test result, researchers obtained nasal swabs from 31 study participants 0-16 years old. Participants were sampled multiple times over several days until they had a negative test result. Parents from two families that had multiple children who were infected were included in the study too.
Two swabs from the front part of the nose were collected from each child each time they were sampled. Material from one swab was tested with a rapid antigen, while material from the second sample was used to screen for the virus by real-time polymerase chain reaction, or RT-PCR, to determine the amount of virus present and to genetically sequence the virus. In a subset of samples, researchers also attempted to culture the virus.
The researchers used a well-established protocol to determine infectiousness. They grew viruses collected from the nasal swabs in cultured cells, observed it kill these cells, then genetically confirmed that the active virus was SARS-CoV-2, the agent that causes COVID-19. This method is considered the gold-standard for determining infectivity. This allowed them to determine whether or not the SARS-CoV-2 viruses collected in the study were actively infectious at the time of sampling.
In the study, all positive results from rapid antigen tests had matching positive results from the previously described culture and RT-PCR test methods. This showed that the rapid antigen test is a reliable marker for the presence of infectious virus.
But there were some samples that were positive by RT-PCR but negative by rapid antigen testing and culture. This confirmed previous observations that PCR test results can remain positive for an extended period after an infection, but that this does not necessarily indicate the presence of a virus capable of infecting a new host.
Genomic sequencing confirmed that all samples used in the study were of the omicron BA.1 viral variant, with strains from a single family—children and parents—showing virtually identical sequences, consistent with viral spread within a household.
Study participants were sampled between Dec. 20, 2021 and Feb. 21, 2022.
The findings show that more time is likely needed to allow infected children safely back to school. They also underscore the importance of having a negative test result before allowing an individual back to school without a mask, as other studies have demonstrated the airborne nature of SARS-CoV-2 transmission.
The new research comes on the heels of changing, and sometimes confusing, public health guidelines.
In late February, the Florida Department of Health revised its guidelines to shorten the isolation period of school-aged children who tested positive for COVID-19, from 10 days to just 5 after a positive test or symptom onset. This adjustment was based on new Centers for Disease Control guidelines.
But while the CDC recommended that children and adults should then wear a mask around others for an additional five days after their isolation ended, to reduce the risk of onward transmission of the virus, the FDOH did not adopt this recommendation.
“Clearly, at a social level, it is important for children to return to school as quickly as possible after being infected with the COVID-19 virus,"said Dr. Morris. "However, from a public health standpoint, longer periods of isolation, or requirements for a negative rapid test result before return to school, may reduce the risk of further transmission of the virus.”
Additional authors include Zoe M. Lohse, Jerne J. Shapiro, John A. Lednicky, Melanie N. Cash, Inyoung Jun, Carla N. Mavian, Massimiliano S. Tagliamonte, Cyrus Saleem, Yang Yang, Eric J. Nelson, Marco Salemi, and Kathleen A. Ryan. These researchers are affiliated with the UF College of Public Health and Health Professions, UF College of Medicine and the UF Emerging Pathogens Institute.
Written by DeLene Beeland, Science & Medical Writer for the UF Emerging Pathogens Institute.