People who tested positive again after they had been treated for COVID-19 and discharged from the hospital were not contagious, a study has found.

No live virus was detected in those people, and no transmission occurred to any of their close contacts in their communities, Hu Fengyu, a researcher at Guangzhou Eighth People's Hospital affiliated with Guangzhou Medical University, told the media recently.

Hu cited research conducted jointly by a team from the hospital and a team under Zhong Nanshan, a prominent respiratory expert. The report on the study was published in China's National Science Review in October.

The study was based on 837 people who had acquired the Delta variant — either locally or overseas — and who were treated at the hospital last year.

Of the total, 514 patients retested positive after they were discharged. The virus found in those who retested positive was inactive — dead or just viral fragments — Hu said.

The patients had recovered from pneumonia or were in the recovery process. The majority of them had no symptoms. A small number said they felt unwell in the throat or nose but did not need to be hospitalized again, said Li Feng, another researcher at the hospital.