Officials are investigating whether the variant had spread at a Chinese restaurant at the Festival Walk shopping mall in Kowloon Tong.
The 44-year-old aircrew member returned to Hong Kong on Christmas Day and he had lunch with his family at the restaurant, Moon Palace, on December 27.
He was confirmed with the variant on Wednesday.
A 76-year-old family member subsequently tested preliminary positive for the virus.
The 76-year-old lives at Wing Chak House in Shek Kip Mei, and residents there have been put under an overnight lockdown and ordered to get tested for Covid.
A 34-year-old construction worker, who had lunch at the restaurant around the same time, also tested preliminary positive for the virus. He lives at a village house in Tuen Mun.
The Centre for Health Protection said officials had collected 44 environmental samples from the restaurant and are assessing whether the virus had been transmitted there.
The restaurant has been closed for disinfection.
Meanwhile, another Cathay Pacific aircrew member – a 47-year-old man – who returned to Hong Kong from the United States on Christmas Day, has also tested preliminary positive for the virus.
The building where he lives, Block A of Hoi Tao Building in Kennedy Town, has also been put under an overnight lockdown. Residents are required to get tested for Covid.
The aircrew member has been triple jabbed with the BioNTech vaccine.