The study found that delaying treatment until a patient's immune system is badly damaged nearly doubles the risk of dying in the next few years compared to patients whose treatment started earlier.
Doctors have thought it would be better to spare patients the side effects of Aids drugs as long as possible.
Those with Aids advised to take their drugs
"The data are rather compelling that the risk of death appears to be higher if you wait than if you treat," said Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, which helped pay for the study.
If the results prompt doctors to change practice - as Fauci and other Aids specialists predict - several hundred thousand people who are not taking Aids drugs now would be advised to start. The study was reported Sunday at an infectious diseases conference in Washington.
HIV ravages T-cells - "helper cells" of the immune system that fight off germs. Once that happens, people can fall prey to a host of diseases that prove fatal.
Powerful drug combinations available since the mid-1990s have transformed HIV infection into a manageable chronic condition rather than the death sentence it once was. But they can cause heart and cholesterol problems, diarrhoea , nausea and other side effects. They also must be taken faithfully or resistance develops and the drugs stop working. That is why guidelines by the US government and the International Aids Society recommend that patients who are not yet having Aids symptoms delay starting on the drugs until their T-cell counts fall below 350 per cubic millimeter of blood (healthy people have more than 800).
The South African HIV Clinicians Society also currently recommends starting antiretroviral treatment at T-cell levels below 350 per cubic millimetre.
The current T-cell level for the commencement of treatment in the South African public health system is much lower than this at 200 per cubic millimetre. There is however a strong suggestion that this figure will be pushed upwards as new health minister Barbara Hogan reassesses some of the country's Aids policies.
How the study was done
"There was this thinking, maybe the drugs were worse than the disease. If you could wait as long as you possibly could wait, you would have fewer side effects," said Dr Robert Schooley, infectious diseases chief at the University of California, San Diego.
The new study is the largest to look at whether that advice is sound. Researchers led by Dr Mari Kitahata of the University of Washington in Seattle pooled information on 8 374 people in the United States and Canada with T-cell counts of 351 to 500 from 1996 to 2006. About 30% started taking Aids drugs right away; the rest waited until their T-cell counts fell below 350, as guidelines recommend.
"We found a 70% improvement in survival for patients who initiated therapy between 350 and 500" compared to those who waited, Kitahata said.
Two other recent studies found that people who start taking Aids drugs while their T-cell count is above 350 have a better chance of getting their count back to normal than those who start later. Another key study found that briefly interrupting treatment to give patients "drug holidays" puts them at grave risk.
"These studies have all shown the same thing - that we were starting too late" and need to keep treatment going once it starts, said Schooley. He helped write the Aids society guidelines and consults for several companies that make Aids drugs.
People still being tested too late
The bigger problem is that as many as a third of people diagnosed with HIV only discover they are infected after their T-cell counts already have fallen below 350 and they have serious complications.
"People are still being tested and identified way too late," and the new study shows how important it is to test and find people sooner, said Dr Daniel Kuritzkes, an Aids specialist at Brigham and Women's Hospital in Boston. Newer drug combinations that have come out in recent years have fewer side effects. Also, some require only a pill or two a day, making adherence less of an issue.
These advances and the new study justify a fresh look at the guidelines, Fauci said. He predicted that doctors would not wait for them to change to start treating patients sooner.
The new study's findings do not apply to HIV patients who also have hepatitis, kidney damage or other medical problems, or who are pregnant - doctors have long advised that these people start treatment as soon as they are diagnosed. - (Sapa. October, 2008)