HONG KONG: Stool tests may be more effective than respiratory tests in identifying COVID-19 infections in children and infants since they carry a higher viral load in their stool than adults, researchers at the Chinese University of Hong Kong (CUHK) said.

Stool samples may carry the virus even after it has cleared from a patient’s respiratory tract and that could lead to better identification of asymptomatic cases, particularly in infants and others who have difficulty providing nasal or throat swabs, CUHK researchers said in a press release on Monday.

The potential for stool testing in young people was a conclusion reached after researchers from CUHK’s Faculty of Medicine carried out stool tests on more than 2,000 asymptomatic children and others who needed such tests who arrived at Hong Kong airport from March 29. As of Aug. 31, of samples collected, six children were confirmed with a COVID-19 infection.

Paul Chan, the chairman of CUHK’s Department of Microbiology and associate director of the Centre for Gut Microbiota Research, said the viral load in the stool of infants and children was “many times higher” than that in adults, and could be equivalent to that of adult respiratory samples.

The activity of viral infection and replication also persists longer in the guts of infants and children, he said.

“Stool specimens are more convenient, safe and non-invasive to collect in the paediatric population and can give accurate results,” Chan said in the CUHK press release.

This makes stool tests “a better option for COVID-19 screening in babies, young children and those whose respiratory samples are difficult to collect.”

Researchers also investigated the stool samples of 15 COVID-19 patients in Hong Kong between February and April and found active gut viral infections in seven of them even in the absence of gastrointestinal symptoms.

Three patients continued to display active viral infection up to six days after clearance of the virus from their respiratory samples.

The finding highlights the threat of potential faecal-oral viral transmissions, the researchers said.

They also said there was more than one coronavirus patient in Hong Kong who had a positive stool test, while respiratory tests were negative, which could mean stool tests were “more effective” for screening specific groups of people.

The study of 15 adults was published in the international medical journal GUT.