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Lower "Community Viral Load" in SF Linked to Fewer New HIV Cases
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18th Conference on Retroviruses and Opportunistic Infections, February 27-March 2, 2011, Boston
Mark Mascolini
A falling "community viral load" in San Francisco since 2004 correlated with fewer HIV diagnoses, a result that will cheer proponents of a test-and-treat strategy to controlling the HIV epidemic [1]. The San Francisco findings support earlier results reported in British Columbia, Canada [2].
Some researchers hypothesize that aggressively increasing voluntary HIV testing rates and starting antiretroviral therapy in everyone who tests positive will limit the spread of HIV by lowering viral load in whole communities and thus curbing chances that HIV-positive people with infect others. The feasibility of this hypothesis--called test-and-treat--is being assessed in a pilot study in Washington, DC, and the Bronx, New York. A controversial modeling study using data from South Africa projected that universal voluntary HIV testing and immediate therapy would slice HIV prevalence to under 1% in 50 years [3].
The San Francisco Department of Public Health has implemented several strategies that do not add up to a test-and-treat policy but that reflect the tenets of test-and-treat. These policies include expansion of HIV testing, linkage to and retention in HIV care, and earlier initiation of antiretroviral therapy. Department of Public Health guidelines recommend evaluating all HIV-positive people for antiretroviral therapy. Department researchers hypothesized that these policies would decrease community viral load across San Francisco and thereby lower the rate of new HIV infections.
The investigators estimated community viral load in four ways: averaging (1) most recent, (2) minimum, and (3) maximum viral load for every HIV-positive person in the past year, and (4) by log transforming the average most recent viral load. Viral load data came from San Francisco's comprehensive HIV/AIDS case registry.
Average CD4 count at HIV diagnosis remained consistently above 400 from 2004 through 2009. But from 2007 to 2009, average CD4 count when antiretroviral therapy began jumped from 357 to 445. Time from HIV diagnosis to virologic suppression plunged from 32 months in 2004 to 8 months in 2008, and to 5 months in 2009 (P < 0.001). Meanwhile, time from starting antiretrovirals to virologic suppression dropped from 18.8 months in 2004 to 2.8 months in 2009 (P < 0.001).
All four measures of community viral load fell significantly from 2004 through 2009 (P < 0.001 for most recent, P = 0.003 for minimum, P = 0.010 for maximum, and P < 0.001 for log transformed). Over the same period, the number of newly diagnosed HIV cases dropped from 864 in 2004, to 737 in 2005, 590 in 2006, 588 in 2007, 540 in 2008, and 506 in 2009 (P < 0.001). All four viral load declines were significantly associated with decreases in newly reported cases of HIV (P < 0.001 for all).
The San Francisco researchers acknowledge certain limitations of their analysis, including exclusion of undiagnosed HIV infections, acutely infected people, and people who did not have viral load reported. The investigators plan to analyze these date in greater detail according to demographic traits, geography, and risk transmission categories.
The Department of Public Health team does not claim that their findings validate the test-and-treat concept, but the title of their report [1] poses that possibility.
References
1. Das M, Chu P, Santos GM, et al. Success of test and treat in San Francisco? Reduced time to virologic suppression, decreased community viral load, and fewer new HIV infections, 2004 to 2009. 18th Conference on Retroviruses and Opportunistic Infections. February 27-March 2, 2011. Boston. Abstract 1022.
2. Montaner JS, Lima VD, Barrios R, et al. Association of highly active antiretroviral therapy coverage, population viral load, and yearly new HIV diagnoses in British Columbia, Canada: a population-based study. Lancet. 2010;376:532-539.
3. Granich RM, Gilks CF, Dye C, De Cock KM, Williams BG. Universal voluntary HIV testing with immediate antiretroviral therapy as a strategy for elimination of HIV transmission: a mathematical model. Lancet. 2009;373:48-57.
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