A 17-year-old girl and her mother were confirmed with the highly contagious strain over the weekend, and the girl’s elder sister has also tested preliminary positive.
But they had not left Hong Kong for a while and authorities have so far been unable to find the source of their infection.
Speaking on an RTHK programme on Monday, Ho said he believes the family was infected by a patient who had been overseas and whose infection was not picked up during the quarantine period.
“What can be done now, is to contact people who arrived in the past 3 to 4 weeks from places categorised as high risk, and have left their quarantine hotels. Authorities should trace their contacts, and conduct both antibody tests – which are currently not being done now – as well as nucleic acid tests,” he said.
Ho said this would involve testing around two to three thousand people.
“If any cases were missed earlier, their antibody tests would now be positive. Trace the contacts from there and see how they are linked to the [infected] family. It’d be easier that way, because so far we still can’t find the family’s source of infection and we don’t know how many cases there are in the community,” Ho added.
He said whether the cases lead to a new wave of infections depends on whether there are any super-spreading events in the coming two weeks which might involve a lot of people staying indoors for a long period of time without wearing masks.
Ho also called on authorities to step up anti-epidemic controls to guard against imported cases – by doing antibody tests both at the airport and shortly before the end of the hotel quarantine period for arrivals.