Oct. 1 (Bloomberg) -- The AIDS virus is infecting more women, heterosexual couples and gay men in China as the epidemic spreads from intravenous drug users to the general population, a study has found.

Infections transmitted by heterosexual contact rose to 38 percent of all cases in 2006, according to a study in Yunnan province. The proportion of cases in intravenous drug abusers in Yunnan declined to 40 percent that year after accounting for 100 percent of all infections in 1989. Nationally, infections have risen in women and shot up eightfold among men who have sex with other men.

The study, to be published tomorrow in the journal Nature, reported data from Yunnan, a major site of the AIDS epidemic in southwestern China. Chinese researchers who collaborated on the study cited a ``dramatic increase in sexual transmission'' that overcame prevention programs.

``HIV/AIDS is spreading beyond the high-risk populations,'' said study author Linqi Zhang, executive director and professor at the Comprehensive AIDS Research Center at Tsinghua University in Beijing, in a Sept. 29 e-mail. ``It is the responsibility of every citizen to help control the further spread. More needs to be done in a much bigger and more effective manner.''

As of October 2007, an estimated 700,000 people in China were infected with the AIDS virus, HIV. Although the prevalence remains low, at less than 1 percent of the population, that represents an increase in infections of 8 percent from 2006, according to the study.

AIDS in Yunnan

China's AIDS epidemic stems from the infection of drug users in Yunnan, the study said. Yunnan, often dubbed ``China's Shangri-la'' for its natural beauty, has a history of opium and heroin trade, according to the study. The majority of illicit drugs in China are trafficked through Yunnan from the Golden Triangle countries on its border, and researchers said the AIDS virus was detected in Yunnan's intravenous drug users in 1989.

Researchers analyzed 3.2 million blood samples collected from 1989 to 2006 to determine the rate of infection HIV in Yunnan's population of 40 million. The testing showed 48,951 HIV cases and 3,935 AIDS patients.

The researchers found that the proportion of women infected with HIV rose to 35 percent in 2006 from 7.1 percent in 1996. For every woman infected with the virus in 2006, there were 1.9 men, compared with a 1-to-13 ratio of women to men in 1996.

Ethnic Pattern Changing

The study also showed that by 2006 more of the ethnic majority in China, the Han Chinese, were infected with HIV, accounting for 60 percent of infections. From 1989 to 1995, the Dai and Jingpo minorities were most affected by the virus, the researchers said.

``The high percentage of infected are now due to sexual contact,'' Zhang said. ``It has begun to move from farmer, minority groups in rural areas into worker, Han-majority urban settings.''

The researchers said that the government must expand programs such as condom promotion among female sex workers, drug rehabilitation and needle exchange to slow the rate of infection. Free medical treatment must be provided to those who are infected, the authors wrote.

Summing up the study findings, the authors quoted a Chinese proverb: ``When there is a crisis, there is an opportunity.'' As the AIDS epidemic moves from high-risk drug abusers to others, they wrote, ``there is still a window of opportunity to prevent further spread to the general population. The time to act is now.''

To contact the reporter on this story: Nicole Ostrow in New York at nostrow1@bloomberg.net.

Last Updated: October 1, 2008 13:00 EDT