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HAART reduces HIV infectivity
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By Karla Gale
NEW YORK (Reuters Health) - Highly active antiretroviral therapy (HAART)
reduces the risk of horizontal HIV transmission by about 60%, and thus represents
an important HIV prevention tool, according to findings from the San Francisco
Young Men's Health Study.
"People would be ecstatic if one of the vaccine trials showed 60%
protection," senior investigator Dr. Dennis H. Osmond told Reuters Health. However, the
preventive effects obtained by increasing HAART will be canceled out, he added,
"if get people get too optimistic and increase their risk behaviors."
HAART is presumed to reduce HIV infectivity based on declines in viral load
and selection for less transmissible drug-resistant strains, but there is
little direct evidence supporting this assumption, Dr. Osmond, an epidemiologist at
the University of California, San Francisco, and his colleagues explain in
the January 2nd issue of AIDS.
To quantify the effects of HAART on infectiousness, the authors devised a
probabilistic risk model to analyze the incidence of new HIV infections prior to
and following the introduction of HAART among 534 seronegative subjects
enrolled in 1994.
Based on subjects' reported behavior, the authors found that the average
number of unprotected receptive anal sex partners increased from 0.6 per subject
between 1994 and 1995, to 1.3 per subject between 1997 and 1999. Their
conservative assumptions included a 23% constant HIV prevalence among subjects'
partners, for the periods April 1992 to November 1996 (pre-HAART) and December 1996
to March 1999 (post-HAART).
Their findings indicate per-partner infectivity of 0.120 prior to HAART and
0.048 after HAART became widespread, amounting to an overall 60% decline in HIV
infectivity (p = 0.028).
The authors caution that increased use of HAART was accompanied by increases
in unprotected sexual behavior, and that community-wide data revealed a rising
incidence in HIV infection soon after the conclusion of their study. Thus,
"the benefit in reduced HIV transmission in the community due to widespread use
of HAART may be offset by increases in unsafe sexual encounters."
"Even in a community where not everybody is treated with HAART and not all
who are treated experience viral load reduction to undetectable levels, there is
significant prevention potential from increasing HAART treatment," Dr. Osmond
concluded. He believes his group's findings can be generalized to undeveloped
countries, where widespread use of HAART has yet to be established.
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