How difficult is it to get HIV? The 7th Conference on Retroviruses and Opportunistic Infections offered a mixed bag of evidence that both soothed and disconcerted.
Heterosexual transmission between married couples did not occur if the viral load was 1500 or less, in a study done in Uganda. Thomas Quinn, MD, from Johns Hopkins University, monitored 415 couples over 30 months and reached that encouraging conclusion. He also confirmed that risk of transmission from the infected to the uninfected partner increased with the viral load. It made little difference whether male or female partner was infected.
But don't go throwing those condoms away just because your viral load is undetectable, there are some serious questions about relevancy of the data. The number of people in the study with a low viral load was small, so statistically speaking, one would not necessarily expect to see any new infections in this subset.
HIV is a rapidly mutating virus. It is not clear that virus held in check by drugs has the same infective capacity as virus held in check by the immune system. Nor is it clear what role non-vaginal sex played in transmission. Many believe that unprotected anal sex carries a higher risk.
Michelle Roland, MD, a researcher at the University of California at San Francisco, told the Associated Press that she knows of one case in that city where a man passed the virus to his female sex partner, even though his plasma viral load was undetectable.
That could be because the testes are behind a blood barrier, which some anti-HIV drugs do not penetrate very well. The virus can have separate patterns of activity and mutation within this tissue compartment. Also, viral load can "blip" or show a short-term rise due to a cold, minor infection, or even a vaccination.
Prevention messages within the gay community have long taught that oral sex is "safer" than unprotected anal sex. Some have been lulled or deluded themselves into thinking that low risk meant no risk. They were shocked to read a report that assigned 6.6 percent of HIV infections in one study to oral sex. Beth Dillon, MD, from the Centers for Disease Control and Prevention ( CDC ) , presented the work.
Over a three-year period her research team interviewed 122 patients in San Francisco who were recently infected [ within the last 12 months ] , to ascertain how they became infected. It found eight who claimed to engage only in oral sex, or who always used condoms when getting fucked. While condoms are highly effective in preventing the transmission of HIV, they are not 100 percent effective. Aside from the noticeable complete break, from time to time a small bit of material may slip through, as illustrated by the occasional pregnancy, even though a condom was used during sex.
Seven of the eight performed oral sex to orgasm, little is known of the viral load of their partners. Several likely had gum or mouth disease at the time of infection, which may have facilitated transmission. Use of poppers, which dilate blood vessels and hence exposure to HIV, was not recorded. The study did not report information on the number of sexual contacts each patient had, so it offers nothing on the relative risk of each contact.
"It's a little piece of evidence," said James Learned, an educator with the Community Research Initiative on AIDS ( CRIA ) . "But there are big questions in it." He urged people to read it "in context" and not get too upset or discouraged. Oral sex is still more than a hundred times less risky than unprotected anal sex.
"Is there original immunogenic sin?" asked Gary Nabel, MD, director of the Vaccine Research Center at NIH. Many believe that once infected with HIV, one cannot become infected with a second strain. The few exceptions to the rule have been attributed to virtually simultaneous exposure to two viruses.
J.B. Angel, MD, documented the first example of "superinfection," where a second HIV infection occurred years after the first. The subject was a patient at the Ottawa Hospital in Canada who was diagnosed with HIV in 1989, a blood sample was taken and stored. He eventually went on a combination regimen and his health was stable when he began a relationship with another HIV-positive man in the fall of 1997. They did not use condoms. Soon his regimen began to fail and his disease began to progress rapidly.
The researchers ran a genetic analysis of the patient's virus from 1989 and 1998. The later sample contained gene segments that were not present in the early sample, and were unlikely to have evolved from it. Those new segments did match segments found in his partner's virus. Angel concluded that superinfection had occurred and led to more rapid progression of HIV disease.
Further complicating the infectious picture is the story of prostitutes in Nairobi, Kenya, whom researchers have followed for years. The women did not seem to become infected with HIV despite repeated exposure to the virus. Researchers speculated that something in their immune system allowed them to fight off infection. It was the basis for hope that a preventative vaccine could be developed.
But increasing numbers of the women began turning seropositive. It came when they either retired from the profession or adopted safer-sex practices that reduced their exposure to HIV. The ironic hypothesis that observers have proposed is that it was the very massiveness of their exposure to HIV that somehow contributed to the prostitute's protection.
Healthcare workers exposed to HIV on the job through needle sticks or other means have long had the option of immediately beginning a month of antiviral therapy. The theory was that it might knock out the virus before infection could become established. There is no definitive data on the effectiveness of this approach.
The San Francisco Department of Public Health and UCSF decided to try it with non-job related exposure to HIV. The Post-Exposure Prevention ( PEP ) program offered to people within 72 hours of exposure a course of four weeks of therapy [ AZT/3tc ] and periodic follow-up out to one year.
Mitchell Katz, MD, said that 401 people enrolled in the program in its first 16 months of operation. Anal sex was the greatest exposure risk at 57 percent, while oral sex was only 4 percent. More than half, 55 percent, did not know the serostatus of their partner. These were not highly promiscuous people. Katz explained, "Even though they were high risk exposures, generally they had relatively few partners and were unlikely to have had multiple unsafe exposures."
Repeat visitors were not common, only 12 percent within six months. Katz related how one young man returned four times in five months, each time vowing to be more careful having sex with his HIV positive boyfriend. It has been eight months since his last visit. "When you think about behavioral change, that is not surprising," Katz said. "Many people quit smoking or drinking multiple times until it sticks. It is not a failure if ultimately we were able to work with him to stop putting himself at risk."
None of the participants have become infected with HIV. But Katz is not claiming that PEP prevented infections. "In a cohort this size you wouldn't necessarily expect to see any seroconversions." He called PEP "a reason for high risk people to talk to a doctor and be counseled to prevent future exposures."