Hong Kong health authorities on Wednesday reported the territory's first case of human swine flu where the person had caught the virus within the city.
Thomas Tsang, controller of the Centre for Health Protection, said the patient, a 55-year-old man, had caught the A(H1N1) virus at an event which another known swine flu patient had attended.
"He had no travel history during the incubation period. We find he had been at the same cocktail party function as the confirmed case on June 5," Tsang told reporters.
Tsang said the man had not travelled outside the city in the previous month.
There have been more than 45 confirmed cases of human swine flu infection in Hong Kong, but all the previous cases caught the virus while travelling abroad.
In a separate case, Tsang said that a 16-year-old secondary school student had tested positive in initial tests for swine flu.
Another seven of the girl's classmates were also displaying flu-like symptoms and officials had advised the school to close, Tsang said.
The latest cases came more than a month after Hong Kong officials confirmed Asia's first case of the A(H1N1) virus, sparking the week-long quarantine of around 300 guests and staff at a city hotel.
The city is very nervous about infectious diseases following the outbreak of the SARS virus in 2003, which killed 300 people here and 800 worldwide after one carrier spread the disease in a Hong Kong hotel.
According to the latest World Health Organisation figures, human swine flu has infected more than 26,000 people in 73 countries across the world, killing 140 people, mainly in Mexico and North America.
WHO assistant director general Keiji Fukuda said Tuesday the WHO was on the verge of declaring an official swine flu pandemic, saying it was working to prepare countries for raising its alarm to the highest level.
On Tuesday, Chinese state media said the country now had 100 confirmed cases of swine flu, while Lebanon, Egypt and Italy all reported fresh infections.