JUDY WOODRUFF:Now to some dramatic findings from arecent AIDS studyand what they suggest about using drugs for the prevention of the disease.

Ray Suarez has the story.

RAY SUAREZ:The power of anti-AIDS drugs in treating patients has been well-documented, but a breakthrough study has found new evidence showing drugs can help prevent the spread of HIV. In fact, the results were so powerful that researchers stopped the trial early.

They followed 1,800 couples in nine countries, including some in Southern Africa. Nearly all were heterosexual. In each case, one partner was infected. Half of the infected partners were given the drugs immediately. Half were given treatment only after their infection level reached a certain threshold. Drugs prevented transmission in the uninfected partners by 96 percent. Out of 28 people who were infected by their partner, 27 were not given the drugs initially.

For more about the findings and the questions they raise, we're joined by the NIH's Dr. Anthony Fauci, thehead of the National Institute of Allergy and Infectious Diseases, which funded the study.

Well, bottom line, what do you know now that you weren't sure of before?

DR. ANTHONY FAUCI,National Institute of Allergy and Infectious Diseases: Well, it's a definitive study because, as you pointed out, it was randomized in the sense of half of the couples got the drug immediately, earlier than you normally would give it to them, and half waited until they reached a certain threshold.

And the difference—we already know from many studies that, if you give a drug to an individual who is infected, you benefit the person. And there was some suggestions that, if you -- if you treat a person, you would lower the probability of their transmitting the infection to their sexual partner.

But this study was definitive and extremely impressive, because the differences were extraordinarily significant. Twenty-seven infections of the 28 were in those whose drug was delayed, and only one in those who received the drug immediately. So, this adds very, very strong scientific credence that you can use treatment of HIV as an effective prevention modality by decreasing the possibility that a person who is infected would transmit it to their sexual partner.

RAY SUAREZ:Didn't we already know that, if you put people on AIDS drugs, it suppresses the amount of virus in their system and makes them less likely to infect someone else?

DR. ANTHONY FAUCI:The answer is, we knew it by observational studies, but what we didn't have was absolute, definitive data that the earlier—and when I say earlier, we mean when a person is early in the course of their disease, before their immune system declines to that critical point, where you absolutely must put them on therapy.

So, we knew that the earlier the better broadly, but we didn't specifically ask the question in what we call a randomized study, where you actually divide them into two groups, and you simultaneously compare the results in each. And when we did that, the data were overwhelmingly positive.

RAY SUAREZ:In some countries with a large HIV-positive population, they don't start treatment...

DR. ANTHONY FAUCI:Right.

RAY SUAREZ:... until the disease has already progressed some way...

DR. ANTHONY FAUCI:Right. Right.

RAY SUAREZ:... because they simply don't have the wherewithal to do it.

DR. ANTHONY FAUCI:Exactly.

RAY SUAREZ:What's the lesson that those countries should take away from this study?

DR. ANTHONY FAUCI:Well, you know, it—there's going to be a lot of soul-searching and examination on the part of authoritative organizations like the WHO, who are very interested in this, a variety of other organizations that are making investments in how—the best way to contain the HIV pandemic.

There's obviously going to be tension between the fact that there are many people with advanced disease who we still have not gotten to, in the sense of getting treatment to them. So, when you're trying to balance an investment in treating people even earlier to prevent infection, we're going to have to balance the risk-benefit of that, in the sense that one of the ways of up-front investment now of treating people early will have a secondary benefit of preventing new infections, which you're ultimately going to have to treat anyway.

So, there's a lot of good active discussion going on right now about what this is going to mean to policy, to guidelines or what have you.

RAY SUAREZ:Well, in places in the world where they don't have money to do everything, they have got to decide with every dollar whether...

DR. ANTHONY FAUCI:Right.

RAY SUAREZ:... they use that money to check on people's status, whether they use that money to do screenings for other diseases, whether they use that money to treat things that have nothing to do with HIV.

DR. ANTHONY FAUCI:Exactly.

RAY SUAREZ:How do you make that call in poor countries?

DR. ANTHONY FAUCI:Well, that's—you make calls based on scientific data. So, just because this study shows this doesn't mean that every country or any country is going to have the resources to be able to enact this, given the points that you just made, that there are a lot of competing priorities.

But it's important to at least have the scientific data, and not guess. Let me give you an example. Right here in this country, we recommend that if—an individual should start therapy if they're infected when their CD4 count is between a certain bracket. And also, they recommend you should even consider if it's higher—in other words, the earlier, the better.

And when the physicians speak to the patient, they have to give them all the data about what the risk and the benefit is. Now, when you consult with the physician and you're trying to make a decision when you should start therapy, the physician can say with absolute certainty that we know from a very good scientific trial that, not only would it be beneficial to you, but it would also dramatically decrease the possibility that you would transmit it to your sexual partner.

Whatever that decision means is up to them. But it's important to know the scientific data. And that's why this study is important.

RAY SUAREZ:If you are in the United States, is it already accepted as a given that you should be put on antiretrovirals once it's found that you're HIV-positive?

DR. ANTHONY FAUCI:Yes.

RAY SUAREZ:Or are there places that make you wait, or there's a waiting list or a shortage here in the United States?

DR. ANTHONY FAUCI:Well, certainly, unfortunately, there's waiting lists.

But there's another issue. There's 1.1 million people in this country who are infected with HIV. 21 percent of them do not know that they're infected. And we and the CDC and a variety of other organizations are trying to push what's called seeking out people, getting them voluntary tested, and putting them on therapy.

The fact that that would be good not only for the individual, but would also prevent them from infecting others, has huge implications, because the people who are transmitting infection for the most part are those who don't even know that they're infected.

And if you know you're infected, and you get on a treatment program, and you are linked to care, you have a dual positive effect, good for the person and good to prevent infection. So it has implications in the developed world, like the United States and Australia and Western Europe, Canada, et cetera. But it also has implications for policy in the developing world.

Treatment can be used as one of a combination of modalities for prevention.

RAY SUAREZ:Dr. Anthony Fauci, thanks for joining us.

DR. ANTHONY FAUCI:Good to be here.