The 26 year-old Pakistani national was the only patient with no clear source of infection among the four local cases reported on Sunday.
Officials believe the man might not be very infectious at the time of his arrest, as his viral load was low.
But Dr Chuang Shuk-kwan of the Centre for Health Protection said the patient had refused to divulge his address or whereabouts, and his failure to cooperate meant people he was with had to go to quarantine.
“Because we cannot get cooperation from the case, so we cannot exclude that they may be the same group of friends who might meet previously, not only on that day,” she said.
“For the other police officers and also ambulancemen, we’ll assess the risks individually on whether anyone of them have close contact with the patient. For example, [whether] they searched him or fought with him, in case he struggled. But if [it was] just normal checking the ID or taking down some information, we won’t count them as close contacts.”
Chuang added that the man arrived in Hong Kong five to six months ago, and has a ‘going-out pass’ issued by the Immigration Department.
A staff at the Castle Peak Bay Immigration Centre, where he had twice visited this month, also has to be quarantined.
Meanwhile, officials reported four imported cases for the day – from Bangladesh, Canada, the US and the Philippines.
With the drop in new local infections, Chuang said she believes the outbreak linked to Ursus Fitness in Sai Ying Pun, which involved 142 patients so far, has now been brought under control.
But she called on members of the public to remain vigilant.
“Although the number has dropped a bit these few days, we still have recorded some unknown cases here and there. So I think there are still some silent transmissions in the community,” she said.
More than 10 people have tested preliminary positive, including a 71 year-old taxi driver who lives in Siu Sai Wan.