Health officials said the 31-year-old woman from the Philippines arrived in Hong Kong last month, and the six tests conducted during her stay at the Penny’s Bay quarantine centre all came back negative.
She went for another test on Thursday after leaving the facility last week, and the sample tested preliminary positive with a low viral load. Her specimen carried the L452R mutant strain, officials added.
But officials said one of her test results after she was admitted to hospital was indeterminate, while her antibody test was positive.
The Centre for Health Protection said due to the presence of a mutant strain, the risk of infection in the building is likely to be higher and so it decided to put Way Man Court on 50-52 Village Road into lockdown.
People who live in the building are required to undergo testing and stay at their homes until the overnight exercise is completed.