Higher HIV levels among men significantly increase the likelihood they will spread the virus that causes AIDS to their female sex partners, according to research conducted by the Johns Hopkins Bloomberg School of Public Health. The study, which appears in the March edition of the Journal of Acquired Immune Deficiency Syndromes, found that with every 10-fold increase in the HIV viral load, the likelihood of transmission increased 81 percent. In addition, the study is the first to document this trend among people infected with HIV subtype E, which is closely associated with heterosexual transmission of the disease and is a common strain in Thailand and other parts of Asia.
"For our study, we examined many factors involved in the heterosexual transmission of HIV from men to women," says Kenrad Nelson, professor of epidemiology at the Bloomberg School. "As the viral loads increased among men, the likelihood of HIV transmission increased dramatically."
For the cross-sectional study, Nelson and his colleagues examined 493 married couples living in Thailand between 1992 and 1998. All the men selected for the study were married and had been diagnosed with HIV during a blood donation drive. The wives were enrolled in the study if they did not have any risk factors for HIV exposure other than having contact with their HIV-positive husbands. The women were examined and interviewed about their sexual history, use of birth control and the length of their relationship with their husband. The couples were referred to medical treatment and counseled extensively about HIV and methods for preventing its transmission.
The study found the greatest correlation between increased viral loads among HIV-positive men and transmission of the virus to their wives. Forty-four percent of the women had contracted HIV from their husbands, the transmission having occurred prior to enrollment in the study. The average viral load of the men was 72,204 copies per milliliter; no transmission occurred to the wives of men with viral loads less than 1,094 copies per milliliter. As the virus levels increased by 10-fold, the rate of HIV transmission increased 81 percent. The results showed that 33 percent of men with a viral load between 5,000 and 15,810 copies transmitted the virus to their wives. The transmission rate jumped to 60 percent for men with viral loads exceeding 500,000 copies per milliliter.
Women who reported having a history of sexually transmitted disease, had their first sexual encounter before age 20 or used hormonal contraceptives also were associated with high rates of HIV transmission. However, the frequency of sexual contact and the length of the relationship were not associated with an increased transmission rate among the women.
"In addition to increased viral load levels, a history of an STD was also a significant factor in HIV transmission from husband to wife," Nelson says. "In this case, the wife must have received the STD from her husband. This supports previous findings that STDs may increase the concentration of HIV in the genital secretions." Continued efforts to reduce STDs in Thailand and other parts of the world might reduce the spread of HIV as well, Nelson adds.
Ninety-seven percent of the men studied were infected with HIV subtype E, which is more closely associated with heterosexual transmission of the disease. Nelson says his findings support the hypothesis that subtype E is more infectious and easily transmitted sexually, but he stresses that more research is needed.
"These findings will add to our knowledge and understanding of HIV transmission so that we can develop more effective policies to prevent the spread of AIDS," he says.
The research was funded by grants from the Contraceptive Research and Development Program, Eastern Virginia Medical School, under a cooperative agreement with USAID.