SHANGHAI, CHINA - The virus that causes AIDS is now spreading fastest in China through heterosexual sex, a trend demanding new strategies to stave off a rebound in the epidemic after years of progress in containing it, a United Nations report said.

Data show that 40 per cent of new HIV infections diagnosed in China were acquired through heterosexual contact, with homosexual sex accounting for 32 per cent and most of the remainder related to drug abuse, which was previously the main source of infections and the government's main focus for prevention.

The rate of infections through heterosexual sex in China tripled between 2005-2007, according to the report released Tuesday in Shanghai by UNAIDS. Since 2007, the number of infections through homosexual sex has more than doubled.

"We are transitioning. We are seeing a shift in the nature of the epidemic," said Michel Sidibe, executive director for UNAIDS. Similar trends in Asia and Africa highlight the need to focus on populations most at risk, such as migrants and sex workers, he said.

"We need to ensure resource allocation is responding to that change," Sidibe said.

China's health minister, Chen Zhu, reported that as of the end of October, the number of Chinese confirmed to be living with HIV-AIDS was 319,877, up from 264,302 last year and 135,630 reported in 2005. But Chen said the actual level of infections is probably near 740,000.

AIDS was the top killer among infectious diseases in China for the first time last year, a fact that may reflect improved reporting of HIV/AIDS statistics in recent years as the country slowly acknowledges the problem.

"In China, we have a long way to go to prevent and control HIV-AIDS," Chen said, while defending the government's policies toward the disease as "open and transparent."

The HIV virus that causes AIDS gained a foothold in China largely due to unsanitary blood plasma-buying schemes and tainted transfusions in hospitals. But last year, health authorities said sex had overtaken drug abuse as the main cause of HIV infections.

The government remains sensitive about the disease, regularly cracking down on activists and patients who seek more support and rights.

HIV's spread has been accelerated by China's thriving sex industry: about 37 million men are estimated to be clients of female sex workers, and surveys show that 60 per cent do not regularly use condoms, the UNAIDS report said.

Such factors contributed to a doubling in women's share of HIV cases in China in the past decade, it said.

China's policy of tolerating the sex industry while outlawing it has long prevented effective efforts to promote education and testing among sex workers, though Chen said the government intends to improve education and prevention.