In 2006, the annual report by UNAids said that 2.5 million people in India were infected with the virus - down from estimates of 5.7 million cases in 2005.
"The single biggest reason for the reduction in global HIV prevalence figures in the past year was the recent revision in India after an intensive reassessment of the epidemic in that country," UNAids said in its report.
UNAids 2007 Report
Breakdown of HIV/Aids cases by region
- North America, 1.3 million.
- Western and Central Europe, 760,00
- Eastern Europe and Central Asia, 1.6 million
- Caribbean, 230,000
- Middle East and North Africa, 380,000
- East Asia, 800,000
- South and South-East Asia, four million
- Latin America, 1.6 million
- Sub-Saharan Africa, 22.5 million
- Oceania, 75,000
Dr Peter Piot, executive director of UNAids, told Al Jazeera that the discrepancy in the figures is due to new methodology.
"Let's take India, today there are over 1,000 sites where the trends in HIV prevalence are being followed... Five years ago, that was just a few hundred.
"So, we have far better and more accurate information from most countries in the world.
"We also have population-based surveys which we didn't have before... We are far more confident that what we have now is the best there is in terms of information about health problems."
Paul de Lay, UNAids director of evidence, monitoring and policy, told a press briefing that the fall in numbers should not be taken as a sign that the battle had been won.
"This is an epidemic where we need eternal vigilance and to never let our guard down," he said.
"If we start to neglect our prevention programmes, the epidemic turns around and starts to increase again."
Kevin De Cock, head of HIV/Aids at the World Health Organisation (WHO), said: "Reliable public health data are the essential foundation for an effective response.
"We need to continue investing more in all countries and all aspects of strategic information relating to health," he added.
The report more than two million people died from the incurable disease in 2007.
Children under the age of 15 totalled 2.5 million of the total number of those living with the virus.
About 1.7 million new infections were recorded in sub-Saharan Africa, two-thirds of the global total, and Aids remains the leading cause of death in the region.
About 22.5 million people living in Africa have HIV/Aids, 68 per cent of the global total, the report said.
In Asia, there are now 4.9 million cases, up from 440,000 last year. Indonesia has the fastest growing HIV prevalence on the continent, while the number of infections in Vietnam has more than doubled between 2000 and 2005.
Unprotected sex is the main factor behind the spread of the virus, with contaminated drug injecting equipment also playing a key role, the report said.