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July 7, 1999

High Rates of Sexual Transmission of HIV Found in Married Couples

A Thailand-based study of heterosexual transmission of the human immunodeficiency virus (HIV) has shown that both the infected male's CD4 lymphocyte count as well as the couple's history of sexually transmitted disease affect whether the female partner becomes infected with HIV. Researchers at the Johns Hopkins School of Public Health looked at 467 Thai couples, most of whom were married, in which the men were found to be HIV-positive when they donated blood. Wives were twice as likely to be infected by their husbands if either partner in the marriage had a history of sexually transmitted disease (STD). Further, the rate of heterosexual transmission to these women was 46.3 percent, substantially higher than the 12 to 24 percent transmission rates reported for heterosexual couples in the United States and Europe.

Nearly 98 percent of the men enrolled in the study said they had had unprotected sex outside the marriage with a commercial sex worker prior to detection of the HIV antibody in their blood. The study appeared in the August issue of The Journal of Infectious Diseases.

Three-hundred-sixty-five of the males in the study had CD4 lymphocyte levels below 500 cells per microliter of blood at baseline--CD4 levels below 500 indicate a debilitated immune system--and the study showed a significant trend for more infection among female partners of men with lower CD4 levels at the time of enrollment. Several previous studies have reported that lower levels of CD4 lymphocytes may be predictive of a more rapid onset of AIDS; however, those women married to men infected with HIV-1 subtype E, the strain of virus that has caused the epidemic in Thailand, had a high risk of infection even when the CD4 cell count was relatively high: 39.2 percent of the women in this study were infected when the men's CD4 levels were relatively high.

Lead author Kenrad E. Nelson, professor, Epidemiology, said, "Several factors could have contributed to the relatively high transmission rate we found, including low condom use, the direction of transmission, frequency of sexual contact during the period of acute HIVinfection, and STD rates." The men in the study rarely used condoms with their wives or regular sex partners prior to be being notified they were HIV-positive.

Heterosexual spread of HIV is the major route of infection in Asia and throughout most of the world. A better understanding of the epidemiology of heterosexual transmission is crucial to controlling the spread of HIV. Few careful studies of sexual transmission of HIV among married couples in developing countries have been reported.

Support for this study was provided by a grant from the Contraceptive Research and Development Program (CONRAD), Eastern Virginia Medical School, under a cooperative agreement with the United States Agency for International Development (USAID). Scientists from Chiang Mai University, Thailand, and the U.S. Centers for Disease Control and Prevention collaborated on this study.

Public Affairs Media Contacts for the Johns Hopkins Bloomberg School of Public Health: Tim Parsons or Kenna Brigham @ 410-955-6878 or