Full HAART Plus Other Interventions May Lessen HIV Epidemic

Brian Hoyle

March 02, 2011

March 2, 2011(Boston, Massachusetts) — Mathematical modeling that enabled the examination of various HIV transmission-related behaviors by men who have sex with men (MSM) suggests that the possibility of HIV transmission is low — but still possible — even after a 12-month highly active antiretroviral therapy (HAART) regimen. Results of a study based on viral load data from nearly 1100 HIV-positive males after the initiation of HAART were presented here at the 18th Conference on Retroviruses and Opportunistic Infections.

"To halt the spread of HIV in [MSM], we have to tackle the key players in transmission: the number of susceptible individuals, the mixing patterns between infected and uninfected populations, the duration of infectiousness, the transmission probability of acquiring HIV through unprotected anal intercourse, and the sexual risk behavior in this group. We decided to move one step backward, and try to longitudinally model the relationship of the per-act and per-partnership unintended anal insertion transmission of HIV-1 RNA after HAART initiation, and the impact on HIV transmission," Vivian D. Lima, PhD, a senior statistician at the British Columbia Centre for Excellence in HIV/AIDS in Vancouver, Canada, told Medscape Medical News.

The study was grounded in the observation that, even in an era of expanded HAART coverage and intervention programs to reduce risky behavior, HIV/AIDS in MSM have remained high.

Researchers used data from an AIDS patient registry in British Columbia to extract information on the viral load of patients who commenced HAART between January 1, 2000 and February 28, 2009. The 1095 people were then followed to February 28, 2010. The intent was to differentiate, using 3 simple equations, the probability of HIV transmission during an individual sexual act (per act) or over time between the same 2 individuals (per partnership).

During the study period, adherence to the HAART regimen among participants exceeded 75%, but was not universal. "Coverage by HAART was not complete, even in Vancouver where healthcare is free," Dr. Lima said in an interview with Medscape Medical News.

At baseline, the typical viral RNA load was 5 log10 copies/mL or higher, and the median transmission probability for receptive anal sex and insertive anal sex was 0.0082 (interquartile range [IQR], 0.0078 to 0.0085) and 0.0013 (IQR, 0.0012 to 0.0013), respectively.

Using the longitudinal data, the mathematical models revealed that over the first 3 to 6 months, a period when the viral load decreased to undetectable levels, transmission of HIV was highest. However, even after 72 months of HAART, the probability of per-act transmission for both receptive and insertive anal sex, although very low, was not 0.

When the per-partnership data were modeled, the first 6 months of HAART was also the time of highest probability of HIV transmission. Contrary to the per-act situation, the probability of transmission increased thereafter, depending on the number of partnerships.

The researchers acknowledge that the findings are only part of the picture.

"One of the limitations [of the study] is the fact that we did not explore the impact of different sexual network structures on HIV transmission," Dr. Lima told Medscape Medical News.

Nonetheless, the study indicates that the undeniable value of HAART coupled with other interventions that can be financed by available medical coverage might drive a reduction in AIDS among MSM.

"The data are interesting, but are not compared to the actual treatment data of subjects. They are using data based on viral load, which does not consider the diagnosis of AIDS," John M. Murray, MD, from the National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, Sydney, Australia, told Medscape Medical News.

"The study is really an exercise to show how shifting various factors can affect the spread of HIV," said Dr. Lima.

Dr. Lima and Dr. Murray have disclosed no relevant financial relationships.

18th Conference on Retroviruses and Opportunistic Infections (CROI): Abstract 486. Presented February 28, 2011.

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