HIV Transmission Still Possible After 12 Months of HAART

Brian Hoyle

March 15, 2011

March 15, 2011 (Boston, Massachusetts) — Mathematical modeling examining various HIV-transmission-related behaviors by men who have sex with men (MSM), using viral load data from nearly 1100 HIV-positive men after the initiation of highly active antiretroviral therapy (HAART), suggests that the possibility of HIV transmission is low, but not 0, even after 12 months of treatment. Those findings were reported 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 by unprotected anal intercourse, and the sexual risk behavior in this group. We decided to move 1 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, senior statistician from the British Columbia Centre of Excellence in HIV/AIDS, Vancouver, Canada, told Medscape Medical News.

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

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

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

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

Using the longitudinal data, the mathematical models revealed that during the first 3 to 6 months of HAART treatment, 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, Dr. Lima reported.

When the per-partnership data were modeled, the first 6 months of HAART was also the time of highest probability of HIV transmission. However, in contrast to per-act transmission, 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 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, might drive the reduction in AIDS among MSM.

"The data are interesting, but they are not compared with 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, PhD, 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.

The authors have disclosed no relevant financial relationships.

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

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