Gender Differences in Risk of HIV Transmission

In heterosexual couples where one partner is HIV-positive, viral load, or the amount of detectable virus in the blood, is a much stronger predictor of the risk of transmission in women than in men, according to a study by researchers at the University of Alabama at Birmingham (UAB).

Posted on October 8, 2001 at 10:33 a.m.

BIRMINGHAM, AL — In heterosexual couples where one partner is HIV-positive, viral load, or the amount of detectable virus in the blood, is a much stronger predictor of the risk of transmission in women than in men, according to a study by researchers at the University of Alabama at Birmingham (UAB). Details of the study were published in a recent issue of the journal AIDS Research and Human Retroviruses.

“Although we’ve known that high viral loads are associated with a person’s risk of transmission, it appears that women with high viral loads are much more contagious than men with high viral loads,” says Dr. Susan Allen, associate professor of epidemiology and international health with the School of Public Health at UAB.

In the United States, heterosexual transmissions of HIV represent a rapidly increasing number of new infections. And in sub-Saharan Africa, where the study was conducted, heterosexual transmission is the primary means by which the virus is spread.

The study followed 1,022 heterosexual couples for periods of two to 67 months over the course of six years. Couples enrolled in the Zambia-UAB HIV Research Project in Lusaka, Zambia, received counseling, free condoms and primary health care.

In 162 couples, the infected partner transmitted the disease to the initially uninfected partner. On average, those who transmitted the disease had significantly higher levels of virus in the blood than those who did not transmit the disease. However, women who transmitted the disease had four times the viral load of those who did not, while men who transmitted the disease had only one-and-a-half times the viral load of those who did not.

Findings may have important implications for the role of HIV therapies and vaccines in reducing viral loads and the spread of the disease. “The study indicates that therapies to lower viral loads could have a significant impact on reducing the risk of transmission, particularly from women to men,” says Allen. “However, the majority of the world’s HIV infections are in the poorest countries where therapies are not available. The development of a vaccine is urgently needed to stem the HIV pandemic.”

The lead investigator of the study was Ulgen Semaye Fideli, M.S.P.H, with the department of epidemiology and international health at UAB. In addition to Allen, other researchers who collaborated on the study are: Rosemary Musonda, Ph.D., with the Tropical Disease Research Center in Ndola, Zambia; Stan Trask, Beatrice Hahn, M.D., and Heidi Weiss, Ph.D., with the division of hematology and oncology at UAB; Joseph Mulenga, M.D., with the Zambia National Blood Transfusion Service; Francis Kasolo, Ph.D., with the Virology and Immunology Laboratory at University Teaching Hospital in Zambia; Sten Vermund, Ph.D., with the department of epidemiology and international health at UAB; and Grace Aldrovandi, M.D., with the department of pediatrics at UAB.