Better Safe Than Sorry

In theory, anyway, combination therapies that reduce viral load to undetectable levels ought to reduce the likelihood that HIV can be transmitted during sex. In medical lingo, people on maximally suppressive anti-HIV regimens are no longer "efficient transmitters" of the virus: they've got far fewer particles of virus circulating in their bodies, so they've got less virus to pass to their partners during unprotected sexual relations.

This makes considerable sense, at least in mathematical terms. The crucial question for all of us is: Does this reduction in viral burden really translate into a reduction in transmission risk? This is the question that must be answered definitively before HIV-positive women consider getting pregnant, and it is one that so-called serodiscordant couples -- one positive, the other negative -- will need an answer to before they contemplate unprotected sex.

In time, epidemiology and clinical experience will provide an answer to this intriguing question. For now, what we have is fragmentary but tantalizing evidence that decreases in viral load do correlate with a decreased risk of transmitting HIV during sex. Some of that early evidence comes from a recent study of 39 seropositive hemophiliacs, all male, and their HIV-negative sexual partners. What researchers at Pittsburgh's Hemophiliac Center of Western Pennsylvania found is that men with higher viral loads were significantly more likely to transmit HIV to their partners during unprotected sexual intercourse.

What does this mean? What this does not mean is that you can resume having unsafe sex once your viral load drops below the level of detection of the tests now being used to measure HIV RNA in the bloodstream. For one thing, "undetectable" means only that the tests we currently use to look for HIV in the bloodstream are not sufficiently sensitive to detect viral particles in the blood once they fall below a certain level. It does not mean that there are no viral particles in the blood. Moreover, when HIV has been eradicated from the bloodstream it can lurk in lymph tissue and other "reservoirs" of HIV infection in the body, waiting to re-enter the bloodstream. And, finally, for all we know it may take relatively few particles of this rapidly replicating virus to cause infection -- in which case transmission of HIV may be possible whenever the virus is present, even when it is present in quantities too small to be detected.

These notes of caution seem especially relevant in light of a recent report on the sexual practices of several hundred HIV-infected men who were treated at hospitals in Massachusetts and Rhode Island. What this survey revealed is that four out of ten infected individuals fail to tell their sexual partners that they have HIV, and two out of three fail to use condoms regularly. Men who had only one sexual partner were three times more likely to have revealed their HIV status than men who had multiple partners, and whites and Hispanics were three times more likely to have done so than blacks.

What these grim statistics tell us is that sex these days is a very risky business, especially in minority communities, especially for those who have numerous sexual partners. In the end, the question of whether people on maximally suppressive antiretroviral therapy are less likely to transmit HIV is almost irrelevant -- because nearly half the people who are infected aren't bothering to share that essential information with their sexual partners, and substantially more than half aren't bothering to use a condom each time they have sex.

The real question, then, is not whether you will or will not infect a sexual partner once your viral load has fallen to "undetectable" levels, but whether or not that partner will reinfect you -- possibly with a drug-resistant strain of the virus -- because he or she hasn't accepted the moral responsibility of saying to each new sexual partner, "You need to know that I am HIV-positive."

Paul A. Volberding, M.D., is Editor-in-Chief of AIDS Care and AIDS Program Director at San Francisco General Hospital.

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