Hong Kong is estimated to have up to 3,200 people with HIV/Aids, almost double the number disclosed in official figures, the United Nations said in a study released yesterday. Up to March, the Department of Health reported that 1,798 people had tested positive for HIV, of whom 570 had developed Aids since monitoring began in 1984. The UNAids Report on the Global HIV/Aids Epidemic released yesterday said that by the end of last year, between 2,100 and 3,200 people in Hong Kong were estimated to be living with HIV/Aids. Of those, 660 were women and fewer than 100 were under 14. Fewer than 100 had died of Aids. But an academic said the figure could be as high as 5,000 and warned cross-border sex was putting the SAR at risk. Professor Joseph Lau Tak-fai, former chairman of the Hong Kong Coalition of Aids Service Organisations, said experts had estimated between 3,000 and 5,000 people in Hong Kong were HIV-infected. However, with continued high-risk behaviour by Hong Kong men who cross the border and have unprotected sex, these figures could rise. 'It is worrying. Our data does not show any change in behaviour. Many people who go to China do not use condoms. The percentage of inconsistent condom usage has remained high over the past few years,' said Professor Lau, who is also director of the Chinese University's Centre for Clinical Trials and Epidemiological Research. He said Hong Kong people mistakenly believed they were not susceptible to HIV. He added the figures had remained low only because vulnerable populations such as homosexual men and sex workers did not mix, because the SAR was not a sex tourism destination and because of the low HIV prevalence among drug users. 'However, because we have high-risk behaviour and we have close links to the mainland, where the Aids [situation] is uncertain, we are not a 'closed' population as are countries like Japan or South Korea which have low prevalence of HIV,' he said. The UNAids report said the Aids epidemic on the mainland - where up to 1.5 million could be infected - was spreading through heterosexual contact. In Guangxi province, HIV infection rates in studies among sex workers showed growth from nil in 1996 to 11 per cent in 2000, the report said. Professor Lau said a recent study in Guangdong found that 13 of 900 prostitutes were HIV-positive. The report was released ahead of the 14th International Aids Conference which begins on Sunday in Barcelona.