HIV treatment dramatically cuts risk of HIV transmission in steady heterosexual couples

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Effective anti-HIV treatment has significantly reduced the sexual transmission of HIV amongst steady heterosexual couples, according to the results of a Spanish study published in the September 1st edition of the Journal of Acquired Immune Deficiency Syndromes. The investigators found that HIV prevalence amongst the initially HIV-negative partners fell from 10% before potent HIV therapy became available to 2% after the introduction of effective antiretroviral treatment. In addition, the investigators also noted that not a single case of HIV transmission occurred in a couple where the HIV-positive partner was taking a powerful combination of anti-HIV drugs.

Even though the study demonstrated the ability of HIV therapy to reduce heterosexual transmission by 80%, the investigators caution that even a small increase in sexual risk-taking could cancel this out and emphasise “the main preventative measure for HIV sexual transmission remains the avoidance of risky sexual practices.”

It is well known that a number of factors can influence the risk of HIV being transmitted during sex. These include sexual practices, stage of HIV infection, the presence of sexually transmitted infections, and the HIV viral load in the infected partner.


observational study

A study design in which patients receive routine clinical care and researchers record the outcome. Observational studies can provide useful information but are considered less reliable than experimental studies such as randomised controlled trials. Some examples of observational studies are cohort studies and case-control studies.

statistical significance

Statistical tests are used to judge whether the results of a study could be due to chance and would not be confirmed if the study was repeated. If result is probably not due to chance, the results are ‘statistically significant’. 


A serodiscordant couple is one in which one partner has HIV and the other has not. Many people dislike this word as it implies disagreement or conflict. Alternative terms include mixed status, magnetic or serodifferent.

mother-to-child transmission (MTCT)

Transmission of HIV from a mother to her unborn child in the womb or during birth, or to infants via breast milk. Also known as vertical transmission.

prospective study

A type of longitudinal study in which people join the study and information is then collected on them for several weeks, months or years. 

Antiretroviral therapy has the potential to dramatically reduce viral load, and the ability of anti-HIV treatment to reduce the infectiousness of HIV-positive individuals has been demonstrated by the use of antiretroviral drugs to prevent mother-to-child transmission of HIV.

The potential for antiretroviral drugs to reduce the risk of sexual transmission of HIV has not been well studied. Therefore investigators from Madrid designed a study looking at HIV prevalence amongst first-time HIV testers whose only risk factor for infection was having a steady heterosexual HIV-positive partner. The investigators compared HIV prevalence amongst individuals recruited before effective anti-HIV treatment became available and those who entered the study when potent HIV therapy was being used.

Since 1987 a specialist clinic in Madrid has been offering counselling and HIV testing for serodiscordant couples. A total of 393 couples using this clinic were included in a prospective observational study to determine HIV transmission risks. Couples were recruited between 1991 and 2003.

Social, demographic and sexual histories were obtained from both partners during structured interviews. Blood tests were performed on the HIV-positive partner to determine CD4 cell count and viral load.

Depending on their date of recruitment, the couples were allocated into one of three groups (1991 - 1995, pre-HAART; 1996 - 1998, early-HAART; 1999 onwards, late-HAART).

In the period before effective anti-HIV therapy became available, the HIV prevalence rate amongst the partners of the patient initially testing HIV-positive was 11%. This fell to 7% in the two years after potent anti-HIV treatment first became available, falling to 2% from 1999 onwards. This fall was statistically significant (p = 0.025).

The investigators found that HIV was only transmitted by patients who were not taking anti-HIV therapy. Not a single partner of an HIV-positive patient taking anti-HIV therapy became infected with HIV.

Other factors associated with HIV transmission were unprotected sex within the past six months (p = 0.048) and a CD4 cell count below 350 cells/mm3 in the HIV-positive partner (p = 0.025).

The prevalence of sexually transmitted infections in the partner who was initially diagnosed with HIV fell from 10% in the pre-HAART era to 1% between 1999 and 2003, and the presence of a sexually transmitted infection was not found to have a statistically significant association with the risks of HIV transmission.

The investigators conclude, “after the introduction of HAART, an important decrease in HIV transmission has been observed in a thoroughly studied group of steady heterosexual couples, irrespective of any changes in other factors that could affect transmission. These results strongly suggest that combined antiretroviral treatments applied according to current guidelines have a great potential for preventing HIV transmission.” The suggest that “accessibility to long as it is not accompanied by a relaxation in other prevention measures, could greatly contribute to controlling the spread of HIV”.


Castilla J et al. Effectiveness of highly active antiretroviral therapy in reducing heterosexual transmission of HIV. J Acquir Immune Defic Syndr 40: 96 - 101, 2005.