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Infectious Diseases

Updated 01 September 2020

Children can carry Covid-19 virus in their respiratory tracts for weeks, study finds

A recent study found that asymptomatic children can carry the virus for over two weeks, suggesting the need for systematic, wide-ranging tracking of cases.

  • A new study suggests that children may continue to harbour the Covid-19 virus in their throats and noses for weeks
  • The findings also shed light on the question of how likely children are to transmit the virus to others
  • The researchers emphasise strict physical distancing measures and good hygiene as schools reopen

The role of children in the transmission and dynamics of SARS-CoV-2, the virus that causes Covid-19, was not entirely clear at the beginning of the pandemic. However, in the meantime, several studies have helped to clear up any doubts.

A new study by South Korean researchers found that children can carry the virus in their noses and throats for weeks. They also found cases of asymptomatic (without symptoms) and pre-symptomatic (not looking or feeling sick at the time, but eventually developing symptoms) infection – a discovery that might help to explain the silent spread of SARS-CoV-2.

The study was published in the journal JAMA Pediatrics.

Mild cases can remain symptomatic for a long time

For the study, researchers looked at data on 91 asymptomatic, presymptomatic, and symptomatic children diagnosed with Covid-19 between February and March at 22 centres throughout South Korea.

Overall, 71 children (78%) displayed symptoms, which included fever, cough, diarrhoea, abdominal pain and loss of smell or taste.

However, they found that 20 of these children did not display any obvious symptoms and remained asymptomatic throughout the study. Another 18 children were pre-symptomatic.

In those who were symptomatic, symptoms lasted from one to 36 days.

Another critical factor the researchers mentioned was that, according to the data, only 8.5% of those paediatric patients with symptoms were diagnosed with Covid-19 at the time their symptoms began, as most (66.2%) of the symptomatic patients showed symptoms that were not recognised before diagnosis, while 25.4% developed symptoms after they were diagnosed.

"This suggests that even mild and moderately affected children remain symptomatic for long periods of time… [and] this highlights the concept that infected children may be more likely to go unnoticed either with or without symptoms and continue with their usual activities, which may contribute to viral circulation within their community," Dr Roberta DeBiasi and Dr Meghan Delaney, both of Children's National Hospital in Washington, DC, wrote in an accompanying editorial. Neither was involved in the research.

Research adds to the belief that children are silent spreaders

This study lends weight to previous findings that children are "silent spreaders" of the virus.

"In this case series study, inapparent infections in children may have been associated with silent Covid-19 transmission in the community," the researchers wrote.

Earlier in August, Health24 reported on a study that reported a significantly higher level of virus found in the airways of infected children, compared to hospitalised adults in ICUs (intensive care units) for Covid-19 treatment, suggesting that children do play a key role in transmitting SARS-CoV-2.

"Interestingly, this study aligns with adult data in which up to 40% of adults may remain asymptomatic in the face of infection," DeBiasi and Delaney wrote.

Virus remained in respiratory tract

The researchers also report that genetic material from SARS-CoV-2 was detectable in the children for a mean of 17.6 days overall.

In the children who were asymptomatic, the virus was detectable for 14 days on average.

Since the date of initial infection wasn't identified, there is a possibility that the virus remained in the children’s respiratory tract even longer, they wrote.

Does this mean they were spreading the virus during this time?

Not necessarily. According to Calum Semple, a professor in child health and outbreak medicine at the University of Liverpool, the presence of the virus genetic material in swabs does not necessarily equate with transmission, particularly in people who do not have important symptoms such as cough and sneeze. Semple was not involved in the study and commented in a statement.

DeBiasi and Delaney also wrote that "sensitive molecular detection methods may detect viable, infective virus but also nonviable or fragments of RNA with no capability for transmission".

Despite this, the two authors further wrote that the latest study can be used by public health officials when considering the spread of the virus in schools. "A surveillance strategy that tests only symptomatic children will fail to identify children who are silently shedding virus while moving about their community and schools," they wrote.