He tested negative, then positive weeks later

Nanjing, Jiangsu province, reported a new asymptomatic case of COVID-19 on Thursday — a 19-year-old patient who did not test positive until four weeks after arriving in China.

The patient, surnamed Zhou, arrived in Nanjing from the United States on Aug 11. He tested negative twice during his two-week quarantine at a designated hotel before going to his home in the city's Jianye district.

Zhou tested negative again on Sept 1, but then came up positive on Tuesday and Wednesday. He has been transferred to Nanjing Public Health Medical Center, a designated hospital for treating COVID-19 patients, for further observation.

The hospital has confirmed that Zhou is an asymptomatic coronavirus carrier.

The local health department has quarantined people who had been in contact with Zhou and warned the public to take responsible precautions.