The man arrived in Shanghai on Sunday from northeast China's Jilin Province. He visited the Zhongshan Hospital affiliated to Fudan University the next day and tested positive for COVID-19 without showing symptoms.
He was sent to a designated hospital for medical observation and treatment.
In April, the man was diagnosed as a confirmed imported case of COVID-19.
So far, Shanghai authorities have traced 23 close contacts who have tested negative and have been quarantined. The man's activity areas have been disinfected.
On Wednesday, authorities in central China's Hubei Province said a woman had again tested positive for COVID-19, months after recovery.
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