A COVID-19 patient who had recovered in Pingdu, a county-level city in Qingdao, Shandong province, tested positive for the virus again on Wednesday, the local health authority said on Thursday.

The 34-year-old patient, surnamed Liu, was diagnosed as a confirmed case of COVID-19 on March 6 when he was isolated in Guangzhou, Guangdong province, after returning from Dubai, United Arab Emirates, where he had been working, the Qingdao municipal health commission said.

Recovering after treatment, Liu returned to Pingdu and continued to monitor his health. Follow-up tests had been negative until a positive result came back on Wednesday, 28 days after he had been discharged from the hospital.

Now he is under medical observation at a designated hospital. He is said to have no close contacts, since he lived alone.

The commission said residents should not worry, as no patient, once recovered, is known to have passed a new infection to others.