The 18-year-old man was confirmed as a local case on December 16, 2020, and recovered and was discharged after treatment at hospital two weeks later.
He tested negative for the virus before travelling to Macau via the Hong Kong-Zhuhai-Macao Bridge Port on Sunday.
But he tested “weakly positive” for the virus on Tuesday during quarantine in Macau. He also has antibodies against Covid-19.
The CHP said, as a precaution, the man’s close contacts would be sent to quarantine, and residents who live in the same Pok Fu Lam building as him are required to get tested for Covid.
Meanwhile, the CHP reported one imported Covid-19 case.
The 45-year-old man, who doesn’t have any symptoms, flew in from Sri Lanka and carries a mutant strain of coronavirus.