A recent study and an accompanying editorial published Sept. 5 in the New England Journal of Medicine cast doubt on the widely held assumption among HIV-positive persons that they can't be re-infected with the AIDS virus.

The research findings could have profound implications for prevention and the search for an AIDS vaccine, AIDS experts say.

The "HIV-1-Superinfection" study documents the case of a 38-year-old HIV positive man who became infected with a second strain of the AIDS virus. He acquired the first strain of HIV — primarily found in Southeast Asia — in 1998.

For 28 months, the man had only that strain of the virus and was treated with a four-drug regimen, which ended because of drug toxicity. The man later traveled to Brazil and had unprotected sex, according to the study. Three months after the treatment ended and three weeks after the unprotected sex, the man was "superinfected" — or re-infected with a second strain of HIV that is "endemic" to Brazil, the study reports.

This is the second documented case of HIV reinfection. The first was confirmed in July 2002 in the Journal of Virology, said Bruce Walker, author of the study and director of Partners AIDS Research Center at Massachusetts General Hospital.

In that instance, an HIV-positive intravenous drug user in Thailand became infected with a second HIV after sharing needles with another drug user. That article didn't get as much attention as the "Superinfection" study, he said.

The "question of superinfection has been around before," Walker said. "But, the public health implications of this [superinfection] study can't be denied."

In the editorial that accompanied the latest study, Walker took aim at HIV-positive persons who have long assumed that unprotected sex with HIV-positive sex partners carried no AIDS-related risk for eeither. "Infected and uninfected persons should … exercise the same degree of vigilance to prevent HIV-1 exposure," Walker wrote.

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Risks to HIV-positive men

Philippe Chiliade, medical director of the Whitman-Walker Clinic in Washington, outlines a hypothetical situation in which an HIV-positive person is doing well on AIDS drugs and has unprotected sex with his HIV-positive partner.

"He could acquire a new HIV that is resistant to medication," Chiliade said. "He could end up having to be on two different drug regiments: one for his first HIV and another for his second HIV. It would expose him to another set of side effects.

"It could accelerate the progress of his disease," he adds. "It could speed up his demise."

The superinfection study shows clearly that re-infection is a risk, said Frederick Hecht, associate professor of medicine at the University of California in San Francisco.

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"But it's still not clear how much risk of superinfection there would be for HIV-positive people who begin treatment at a later period of time [than was the case with the patient in the superinfection study]," Hecht said.

Hecht is still advising most of his patients "not to be excessively alarmed," but said the risk of superinfection "is another reason to be cautious about unprotected sex."

After years of telling HIV-positive men to use condoms, the superinfection study finally confirms that re-infection is a threat, said Matthew Tye, managing director of program services for Gay Men's Health Crisis in New York.

"It adds another layer to the conversation and reinforces what we've done in the past," Tye said. "We'll distribute scientific information and educational materials in sex venues, clubs, the streets and parks."

But, prevention won't be easy, said Scott Brawley, director of public policy of AIDS Action in Washington, D.C. Superinfection and safe sex raise difficult questions about personal sacrifice and free will, he said.

"How much should you be able to chose to place yourself or others at risk versus being responsible?" he asked.

The issue of whether HIV-positive persons should engage in protected sex with one another isn't a simple matter, and older patients are "getting tired of having safe sex," Chiliade said.

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"It's easy to say, 'You must have safe sex,' but, it's hard to do all your life," he said. "Who wants to think clearly — to think about condoms during sex? It's such a marvelous moment."

Superinfection could also make it more difficult to develop an AIDS vaccine, researchers say. Vaccines against any virus are usually a "killed" or "weakened, live" form of the virus so that a later exposure to the same virus doesn't take effect because the vaccine has already exposed the patient to it, Chiliade said.