A study by Chinese and US scientists showed that 14.5 percent of patients released from hospitals after undergoing Covid-19 treatment have retested positive for infection.
According to researchers, in a report undertaken by health authorities in southern China's Guangdong province at the end of February, 38 out of 262 participants – all of whom were studied for at least two weeks – retested positive, almost similar to the proportion – 14 percent, reports South China Morning Post.
However, last month's work by a Tongji Hospital team in Wuhan – the central China city at the epicentre of the original outbreak – produced a promising figure of just 3 percent.
The latest study, which was conducted by researchers from Shenzhen 3rd People's Hospital, Beijing Tsinghua Changgung Hospital, Southern University of Science and Technology and MIT, was published on Medrxv.org and has yet to be peer-reviewed.
The subjects had all been patients at Shenzhen 3rd People's Hospital in Guangdong between January 23 and February 25.
The researchers said the results appeared to suggest that younger people were more likely to retest positive, as were those who had suffered only mild symptoms.
Of the 38 patients who retested positive after discharge, just one was aged over 60, while seven were under 14, it said.
Also, of the 38, only "a small number reported a mild cough and chest tightness, which was not worse than before", while none experienced a fever, it said.
The researchers also tested 21 people with whom the 38 subjects had been in close contact and they all came back negative for the coronavirus.
Despite their findings, the researchers said that because of discrepancies in the results found with different test kits, they had not ruled out the possibility that people who had recovered from Covid-19 might become carriers.
The researchers found that 18 of 24 patients who returned a negative result using a commercially available test kit – known as an RT-PCR – actually tested positive when subjected to more "sensitive" tests, according to Feng Zhang from MIT who was a co-author of the study.
Professor Leo Poon Lit-man, who heads the public health laboratory sciences division at the University of Hong Kong, said that although RT-PCR tests were generally reliable, it was possible to have discrepancies in the results they produced.
"If you do a series of tests [on people discharged from hospital], most of the time they will come back negative because the amount of virus in the sample is low," he said. "It will only come back positive after doing multiple tests."
While some studies have suggested that the virus in patients who retested positive was no longer infectious, experts needed to consider how to deal with such cases, Poon said.
China's National Health Commission does not publicly report the number of patients who test positive for the coronavirus after being discharged from hospital.