About two years ago, I attended a continuing education class about HIV and STDs where the guest speaker was Dr. Bernard Branson, a researcher at the Centers for Disease Control and Prevention (CDC). Dr. Branson has an affable, matter-of-fact style. A soft-spoken man, you find yourself listening harder, endeavoring not to miss a word. That day, Dr. Branson talked about reinfection and answered a question: Is it possible to be reinfected with HIV?

From virtually the beginning of this epidemic, there seemed to be a unanimous opinion that HIV-positive individuals could be reinfected by other strains of the virus. Two years ago, Dr. Branson told a roomful of HIV counselors that to date no evidence existed to support the theory of reinfection. He further stated his personal belief, not sanctioned by the CDC, that reinfection does not occur. I was not the only person in that room who bristled. This was radical stuff. And from that day forward I would hear his name and think, "Oh, yeah...that heretic guy from the CDC...I wonder when they'll fire him?"

April, two years later, I found myself sitting in the same room listening to Dr. Bernard Branson one more time. As he was reintroduced I took note of his credentials. He was one of the founders of a Maryland sexually transmitted diseases clinic way back in 1978 that later became an AIDS service organization; he joined the CDC in 1990; and he's one of only a handful of people on the planet who've done comprehensive research about the potential for reinfection with HIV. I'm impressed, but no less skeptical. He's back. And he's talking about reinfection again.

Two years on, Dr. Branson amends his view only slightly: "Reinfection, if it occurs, is rare." And again Branson's personal footnote: "My personal belief is it does not occur." This would be the part where you say to yourself, "I wonder what David thinks?" I think you have to look at the existing data and other opinions.

Dr. David Ho, esteemed AIDS researcher, was quoted in Treatment News magazine saying, "There is little evidence to document that additional superinfection or reinfection with a second strain of HIV occurs at a period of time after infection." Jay Levy, an AIDS researcher at the University of California at San Francisco, states in his article in HIV and the Pathogenesis of AIDS that "in the host, resistance to superinfection appears to occur once the immune system has responded (or after seroconversion). Coinfection between individuals with HIV appears to be an uncommon event." Levy further acknowledges that "the prevalence of infection by more than one strain of HIV-1 in vivo (the body) is unknown but is most probably rare."

A 1997 study published in the journal AIDS, describes the evolution of HIV in an infected couple. One partner, infected by blood transfusion, passed HIV to her partner sexually. They continued having unprotected sexual intercourse. HIV mutates naturally in the body and the genetic makeup of the virus changes over time into closely related versions of the original HIV. In this couple, time showed that the virus diverged separately in each individual, but there was no continual exchange of HIV after initial transmission. This would seem to support the idea that once you're HIV-positive, you're positive. Period.

Similarly, a study from as far back as 1988 in the journal Nature reported on multiply exposed HIV-positive individuals and found no evidence for reinfection or superinfection (simultaneous infection by two or more strains). Researchers did not find HIV-1 strains that were unrelated to the predominant viral forms.

But there's also an as-yet unpublished CDC study first presented at the 11th World AIDS Conference which confuses the picture. Laboratory workers tried to establish a mixed infection in macaques (monkeys). They discovered the monkeys could be dually infected (superinfected) if both viruses were introduced simultaneously or if the second virus was introduced after the first but before seroconversion (the development of antibodies to HIV). But exposing an animal to a second strain of HIV after seroconversion to the first strain did not result in reinfection.

There's other animal research going on at the University of Alabama in Birmingham as reported in the Journal of Virology. These researchers exposed one chimpanzee to several strains of HIV. Two distinct HIV populations did establish themselves and coexist in this chimpanzee. I'm sure I don't have to remind you that we are not macaques or chimpanzees, so any attempt to imply scientific ramifications for human beings based on this research is both irresponsible and faulty. (Personal note: animal studies like these give me the creeps anyway.)

What have we learned? Reinfection research is inconclusive for now. Uncommon. Rare. Little evidence. Unknown. Not exactly the words most of us are looking for here. Research continues. In two more years, maybe Dr. Bernard Branson will tell me and my colleagues that reinfection in humans is not possible, and perhaps it will be more than just his personal opinion; maybe it will be the CDC's official conclusion.

Until more comprehensive human research is done, most of us living with HIV will continue to weigh the risks of positive on positive sex without condoms. Even if you choose to believe that reinfection isn't possible, remember that other sexually transmitted diseases can threaten your health and have been known to contribute to an increased viral load. Sure, we can cure a lot of STDs, but some we can't. Other infections require more medications or unpleasant treatments. It's a personal call, of course, but I advocate continued risk reduction and safer sex techniques especially when having sex with partners of undetermined HIV and STD status.