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Young children under age 5 with mild to moderate COVID-19 had high amounts of SARS-CoV-2 in their upper respiratory tract versus adults or older children, researchers found.

A cohort of 145 patients younger than age 1 month to 65 years separated by age found that the youngest children had significantly lower median cycle threshold (CT) values than older children or adults, suggesting they had equivalent or more viral nucleic acid in their upper respiratory tract than other age groups, reported Taylor Heald-Sargent, MD, PhD, of Ann & Robert H. Lurie Children's Hospital in Chicago, and colleagues.

These differences approximated a 10- to 100-fold greater amount of SARS-CoV-2 in the nasopharynx of young children, the authors wrote in a research letter in .

Importantly, the researchers noted that their findings were limited to detection of viral nucleic acid and not infectious virus.

"Young children can potentially be important drivers of SARS-CoV-2 spread in the general population," the team argued.

Research has been mixed on what role children play in the spread of COVID-19, complicated by school closures in the U.S. in the spring, as well as that data on children has largely been limited. But the subject has come up more frequently with the proposed reopening of schools in the fall.

"Behavioral habits of young children and close quarters in school and day care settings raise concern for SARS-CoV-2 amplification in this population as public health restrictions are eased," the authors said.

They added that children generally present with milder symptoms compared with adults, but that children also "drive spread of respiratory and gastrointestinal illnesses in the population." In addition, the researchers noted that this has been demonstrated with respiratory syncytial virus, where "children with high viral loads are more likely to transmit."

The team performed SARS-CoV-2 reverse transcriptase-polymerase chain reaction (PCR) testing on nasopharyngeal swabs from inpatient, outpatient, emergency department, and drive-through testing sites at a pediatric tertiary care center in Chicago from March 23 to April 27. The investigators then recorded PCR amplification cycle CT values, with "lower values indicating higher amounts of viral nucleic acid."

Patients had mild to moderate illness within a week of symptom onset, and participants included 46 children younger than age 5, 51 children ages 5-17, and 48 adults ages 18 and older. The authors found similar median CT values for older children and adults, but younger children had substantially lower differences in CT values.

These differences persisted in a sensitivity analysis when including those whose symptom duration was unknown. The authors also said they identified a "weak correlation" between symptom duration and CT in all three age groups.

Regarding the public health implications of the findings, Heald-Sargent said this population of younger children will be important to immunize as vaccines against SARS-CoV-2 become available.

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