Children spread SARS-CoV-2 less than adults

A study conducted by researchers in Canada suggests that children may be less likely than adults to spread the novel coronavirus 2 (SARS-CoV-2) with severe acute respiratory syndrome that causes coronavirus disease 2019 (COVID-19).

As recently reported in the Canadian Medical Association Journal (CMAJ), the study found that samples from 175 children aged 17 years or younger were about half as likely to contain culturable viruses as samples from adults.

When SARS-CoV-2 was successfully cultured, samples from children had significantly less viable virus than those from adults.

The team at Cadham Provincial Laboratory in Winnipeg, Manitoba, says the results suggest that children do not appear to be the main drivers of SARS-CoV-2 transmission, which has important public health and clinic implications.

Jared Bullard and colleagues say the study also suggests that the cycle threshold – the number of cycles required for the virus to be detected by polymerase chain reaction (PCR) testing – is used to determine a child’s potential infectivity can be of great value.

A better understanding of child transmission is essential

Public health measures taken to reduce the transmission of SARS-CoV-2 have included the suspension of personal schooling. This decision was mainly based on observations that children previously played a role in the transmission of respiratory viruses such as influenza.

However, Bullard and the team say the role children play in transmitting SARS-CoV-2 remains unclear, given the lack of studies and conflicting results.

“As more jurisdictions consider whether to continue or resume learning in school, daycare, and extracurricular activities, there is a better understanding of the relative contributions of children and adolescents to SARS-CoV-2 transmission compared to adults by crucial. ” You write. “This is particularly important given the increased likelihood of asymptomatic infection in this group.”

Studies lacked a “critical dimension”

An important indicator of the in vivo infectivity is the recovery of the living virus in the cell culture. According to the researchers, almost all pediatric studies of SARS-CoV-2 transmission lacked an assessment of this critical dimension, which limited the ability to conduct a more comprehensive risk-benefit analysis of the role of children in the spread of the virus.

In addition, evidence suggests that SARS-CoV-2 infectivity can be predicted using data such as the cycle threshold generated during reverse transcription PCR (RT-PCR).

The cycle threshold is a relative measure of the amount of genetic material in a sample, with a lower value indicating the presence of more viral genetic material.

What did the researchers do?

The researchers received nasopharyngeal swabs from COVID-19 cases in adults and children and their contacts who tested positive for SARS-CoV-2 between March and December 2020.

SARS-CoV-2 culture positivity rates were quantified and compared between adults and children. The cycle thresholds from RT-PCR and the tissue culture infectious dose of 50% (TCID50 / ml) were also compared between adults and children. The TCID50 / ml is a widely used assay for quantifying infectious virus titers.

What did the study find out?

Of 305 cultured specimens, 97 were from children aged 10 years or younger, 78 from children aged 11-17 years, and 130 from adults (aged 18 years or older).

The team successfully bred SARS-CoV-2 in 93 (31%) of the 305 samples, including 57 (44%) of the samples from adults.

In contrast, the virus could only be cultured in 18 (19%) samples from children aged 10 years or younger and 18 (23%) samples from children aged 11-17 years.

The likelihood of live virus growing from the children’s samples was 55% lower than the adult samples.

For the children aged 10 years or younger and the children aged 11-17 years, the mean cycle thresholds were 25.1 and 22.2, respectively, compared with 18.7 for adults.

For both children and adults, the cycle threshold was a strong indication of the positivity of the SARS-CoV-2 culture.

In addition, the mean TCID50 / ml in the samples from children aged 11 to 17 years was significantly lower at 316 versus 5620 than in the samples from adults. The mean TCID50 / ml did not differ significantly between adults and children aged 10 years or younger.

What are the effects of the study?

The researchers say the results show that RT-PCR positivity does not necessarily equate to culture positivity.

“In children who tested positive for SARS-CoV-2 using RT-PCR, knowing the cycle threshold can be more meaningful for determining a child’s potential infectivity and have an impact on the duration of isolation,” write Bullard and colleagues.

“Given the difficulty of keeping children isolated in the home environment and the significant impact of prolonged isolation on child development and parental function (e.g. loss of work or income), this is a robust tool to help out the end or reduce the need for quarantine. This would be an important public health development, ”the team concludes.

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