The 35 percent drop in HIV cases among people aged 15-24 was the result of better prevention and not due to deaths from AIDS, researchers from the University of Toronto said in a study published on the Web site of the Lancet, a British medical journal.
The researchers singled out efforts by the Indian government, the World Bank and other non-government groups to educate sex workers and men who frequent them about the dangers of HIV, efforts that "appear to have contributed to a drastic decline" in new infections.
The study was conducted by a team of Indian and Canadian researchers who tracked HIV prevalence among 204,050 young women and nearly 60,000 men between 2000 and 2004 in both the north and south of the country.
They found that the prevalence rate in the four southern states of Tamil Nadu, Andhra Pradesh, Maharashtra and Karnataka, which account for about 75 percent of India's HIV infections, fell from 1.7 percent in 2000, to 1.1 percent in 2004.
India has an estimated 5.13 million people with HIV, second only to South Africa, although the percentage of those with the AIDS-causing virus is much lower than in many parts of Africa, where the infection rate is well into the double digits.
Still, there are fears that ignorance and the stigma attached to the disease could hamper prevention efforts and lead to an explosion in new infections across India.
"HIV remains a huge problem in India and we have to remain vigilant," Rajesh Kumar, one of the authors of the study, said in New Delhi on Thursday. "We're not saying the epidemic is under control yet, we are saying that prevention efforts with high-risk groups thus far seem to be having an effect."
In fact, another of the report's authors, Prabhat Jha, warned: "The not-so-good news is that trends in the north remain uncertain and poorly studied."
The survey found that over the four-year period there was no evidence to suggest a decline in the number of men visiting sex workers — just that more people were practicing safe sex.
"What our study shows is that safe sex campaigns do work," Jha said in New Delhi.
He said since HIV awareness campaigns began, the use of condoms among sex workers had increased 70 percent.
The study recommends enhancing surveillance and more testing for sexually transmitted diseases.
While the Indian government's HIV prevention campaign was concentrated on high risk groups such as sex workers, it was important to take the message to wider audiences, Jha said.
"We have to identify the hot spots; highways, factories, places where young men gather, and scale up prevention efforts," said Jha.