A recent study conducted in the United Kingdom assessed the status of HIV infections in heterosexuals versus those currently found in homosexuals. Currently, there are a greater number of HIV-infected heterosexuals in the United Kingdom than HIV-infected homosexuals. Based on their findings, researchers have inferred that it may be possible to further restrict heterosexual transmission of HIV.

Historically, the first HIV infections identified in the U.K. were in homosexual males. However by the mid-1990s, the majority of HIV diagnoses were in heterosexuals. This trend continues to this day.

HIV sub-typing, used to distinguish between the unique genetic variants of HIV, allows for easy analysis of this shift in HIV diagnoses. Previously, HIV-1 subtype B was the main subtype seen in both Western Europe and the United States. However, in 2000, an analysis of subtypes exhibited by HIV-positive heterosexuals in the U.K. showed a drastic change in subtype prevalence in this group. Virus characterization revealed that 35 percent of infected heterosexuals possessed subtype C, 15 percent subtype A, and only 25 percent subtype B. Since this analysis, HIV infection in heterosexuals has shown a strong correlation to non-B HIV subtypes.

Researchers used viral samples taken from approximately 40 percent of the total population of non-B subtype HIV-positive heterosexuals in the U.K. They then evaluated transmission rates using CD4 cell counts (white blood cell counts) and essential DNA coding sequences of the virus sample extracted from each patient.

Their results indicate that acute, or rapid-onset, HIV infection is less common in heterosexual transmission compared to homosexual transmission. Two possible explanations have been proposed for these findings: incidence of partner changes is lower among heterosexual couples, or the risk of transmission in heterosexual intercourse is lower.

In either case, these results are already generating optimism because it is unlikely that higher levels of HIV associated with rapid-onset infection significantly contribute to the heterosexual HIV epidemic. The slower rates of transmission seen in heterosexually transmitted HIV also allow for a larger window for intervention. Early diagnosis and effective treatment programs could help decrease the number of HIV-positive heterosexuals in the HIV epidemic.

For the full research article, please see The Public Library of Science, and for statistics on HIV/AIDS prevalence in the U.K. see the AVERT Web site.