Virus detected in the gut of recovered patients

Covid-19 patients could have prolonged gut viral infections even after they have been cleared of the virus in their respiratory sample, making their stools a channel of infection for the others, scientists from CUHK warned.

The team from the Chinese University of Hong Kong ’s faculty of medicine screened 2,218 stool samples from airport arrivals between March and August, and detected the virus in six children. 

Among them, a two-year-old infant was sent to the hospital after his respiratory sample tested positive at the airport. Although his respiratory sample tested negative on the second day, they still found the virus in his stools in the next 36 days. 

The viral load found of his stool samples was equivalent to that of respiratory samples from adult patients.

Paul Chan Kay-sheung, chairman of the department of microbiology and associate director of the Centre for Gut Microbiota Research at CUHK, said it showed that Covid-19 could still persist in the gut despite respiratory clearance of the virus. 

“[These children] are easily silent carriers as they are asymptomatic with high viral load, and the virus stayed in their body for a relatively long period,” said Chan.

He explained that stool test is a more convenient, safe and non-invasive method to identify hidden transmission links in the community. 

“The stool test is more appropriate for those who cannot follow instructions to take respiratory samples. Obviously, children and infants belong to this category,” Chan added. 

To further study the coronavirus activity in gastrointestinal tracts, the team has also investigated stool samples of 15 Covid-19 patients aged between 20 to 65, among which seven cases had viral gut infections even in the absence of related symptoms.

Ng Siew-chien, associate director of the centre for gut microbiota research at CUHK, said it was unprecedented that Covid-19 was detected in stool samples even though patients didn’t experience any discomfort in their stomachs.

She added the stool specimens contained a large amount of Covid-19 “3’ prime-end DNA”, which favors the virus’s activity and replication.

From yesterday, the university has started operating a test center that would conduct up to 2,000 Covid-19 tests per day, mostly stool screenings.

High-risk groups targeted by the department of health, such as babies and toddlers, would be referred for the test, with results available within a day.

According to the Hospital Authority’s regulation, Covid-19 patients can be discharged if they pass an antibody test, regardless of the virus's presence in stool samples.

But Chan said it’s impossible to conclude that a patient is completely uninfectious after discharged from the hospital, but the infectivity of those who have generated antibodies is greatly reduced. 

He urged discharged patients and their caretakers to stay vigilant and observe strict personal hygiene at home, like cleaning contaminated areas in toilets with proper disinfectants.