MORE than half a million people in Hongkong are highly vulnerable to HIV infection, AIDS experts warned yesterday as they released the territory's first comprehensive survey on the disease. The figure was projected from findings that 7.8 per cent of men and 2.3 per cent of women of the 1,245 respondents confessed to high-risk behaviour, such as casual sex, sex with prostitutes, or sharing needles to inject drugs. Such behaviour was most common among men between 21 and 31 (13.5 per cent) and those who had not married (13.7 per cent). A total of 634 men and 611 women aged between 18 and 56 were interviewed in the survey last year by the Hongkong AIDS Foundation. The findings will be crucial in formulating territory-wide strategies to combat AIDS. Researchers claimed that about 220,000 people were directly or indirectly threatened by HIV infection, according to the survey. But the actual number could be two or three times more, they said. An executive board member of the foundation, Dr Patrick Li Chung-ki, suspected some respondents did not admit they practised high-risk behaviour. None of the male respondents admitted they were homosexual. Dr Li said: ''I think the real number should be two or three times more. We are worried about these people practising risk behaviour and not taking precautions.'' He warned that the problem could worsen more quickly with the spread of the disease, he said. Latest government statistics reveal there are 348 HIV carriers in the territory, but officials estimate there are actually between 4,000 and 7,000 carriers. Dr Li said the foundation would work out its strategy after the release of a final report, which would include more analysis. Saying that the study revealed a ''hidden danger'', Dr Li said future plans would focus on young men and women with steady sexual partners and inform them of the importance of taking precautions when having sex. Researchers were alarmed that 5.3 per cent of married men confessed to high-risk behaviour, putting their wives in danger. Dr Li said more education was needed because only 36 per cent of respondents said they consistently used condoms. And a majority said they were reluctant to use condoms when having sex with their regular partners. Mr Mike Sinclair, an HIV carrier and an education officer at the AIDS Foundation, said the media had to help get the message across. The survey showed that 92 per cent of people obtained information primarily from the television. The survey showed a majority of respondents still held misconceptions about AIDS. Seventy per cent thought AIDS could be transmitted by kissing. A total of 77 per cent thought it could be transmitted by mosquito bites, 41 per cent by coughing and 36 per cent by blood donors. Dr Li siad the misunderstanding explained why the society had so far only shown limited support for HIV infected patients. The survey also found 70 per cent of respondents would avoid daily social contacts with HIV carriers. 'Such negative attitudes correlated with misconceptions about the risk of social contacts in transmission of HIV,' he said.