Doctors say it may soon be possible to quickly predict how effective a particular anti-AIDS treatment will be for HIV infected patients. The development comes at the same time the World Health Organization is calling for governments, the private sector, and U.N. agencies to fund anti-retroviral therapy for three million people worldwide by the end of 2005.

The World Health Organization estimates there are 42 million people worldwide who are infected with HIV, the virus that causes AIDS.

Programs by drug makers to slash prices of expensive anti-retroviral therapies and generic versions of the drugs mean more people are gaining access to Highly Active Retro-viral Therapy treatment, known as HAART.

It usually consists of at least two anti-retroviral drugs that are given to people infected with HIV in the hopes of prolonging their lives. But there is a nagging question.

"The long-term prognosis of patients with HIV who are taking these treatments, who are taking HAART is not really known," explained Matthias Egger, a member of an international group of researchers who looked at the three-year outcomes of 9,000 people on HAART worldwide.

He says normally doctors predict the effectiveness of a therapy by first measuring the amount of virus in the patient.

But in a study published in the journal The Lancet, investigators found that predictions are more accurate later. Patients who had a good response within the first six-months of anti-retroviral treatment did the best. That included patients who had very large amounts of virus in their blood when they started therapy.

"So, it is really difficult to say at the beginning of treatment what [the] prognosis will be," said Matthias Egger. "You really have to see how the patient responds to that treatment. And after six months, as we have shown in our study, it seems to be a good time to look at this initial response and then to gauge the long-term prognosis depending upon that initial response."

In the study, two-thirds of patients with undetectable levels of virus in their blood after six months of therapy continued to do well for three years. Only about two percent of patients experienced a relapse in which the amount of virus in their blood shot up, resulting in illness or death.

"At six months, if they get there, they are fine," he said.

Researchers plan to return to the patients after about five years to see if they are still doing well. Dr. Egger says investigators also want to look at the outcomes of anti-retroviral therapy in developing countries, where the need is greatest.