New public health data from San Francisco and British Columbia indicate that increased HIV testing and viral load–reducing antiretroviral therapy are affecting transmission rates in both locales, according to new reports at the 17th Conference on Retroviruses and Opportunistic Infections (CROI) in San Francisco.
The real personal benefit of HIV testing and care for those found to be positive—delayed progression to AIDS and death—is well established. Less understood is the public health benefit of “test and treat” initiatives, namely whether or not having more people know their positive status and then take treatment to lower their viral loads affects transmission rates in communities with high rates of HIV.
Evidence has certainly suggested this is possible. Studies have shown that HIV-positive people who know their status are likely to take steps to prevent ongoing transmission of the virus. Evidence also suggests that ARV therapy is effective at reducing the risk of transmission in sexual partnerships consisting of HIV-positive and HIV-negative individuals. But in order to justify “test and treat” initiatives—recommending ARV therapy for both personal and public health gains—additional data have been needed.
Fewer Cases in San Francisco
Moupali Das-Douglas, MD, of the San Francisco Department of Health and the University of California at San Francisco, reported her team’s data on Wednesday, February 17. The study evaluated HIV testing practices and the relationship between average viral loads and the number of newly reported HIV cases and the number of new HIV infections between 2004 and 2008.
Das-Douglas reported an enormous reduction in the number of people living with HIV but unaware of their HIV status. In 2004, about 24 percent of people living with HIV did not know they were infected and, in turn, weren’t accessing care or likely engaging in safer practices to reduce the risk of transmitting their infection to others. By 2008, the rate was about 14 percent—a tremendous improvement.
In 2004 and 2005, viral loads among people living with HIV in San Francisco averaged 24,000 copies per milliliter (mL). Starting in 2006, possibly because of national, state and local government efforts to step up testing and linkage to care, viral loads decreased steadily, from 22,000 copies/mL in 2006 to 15,000 copies/mL in both 2007 and 2008—a 40 percent reduction in the average community viral load.
These reductions in viral load were associated with reductions in the annual number of new HIV infections reported to the S.F. Department of Health. There were 798 new HIV cases in 2004, 423 in 2006, 518 in 2007 and 434 newly diagnosed HIV cases in 2008. The reduction in new HIV cases between 2004 and 2008 was statistically significant, meaning that it was too great to have occurred by chance.
Of course, newly diagnosed cases can involve people who have been infected for several years. To correct for this—that is, look for the actual number of new infections occurring annually—Das-Douglas’s group used a model developed by the U.S. Centers for Disease Control and Prevention (CDC) to calculated the estimated incidence of infections occurring annually in the time period specified. Though there appeared to be a 34 percent reduction in the number of new infections between 2004 and 2008, this difference was not statistically significant.
Fewer Cases in British Columbia
Julio Montaner, MD, of the BC Centre for Excellence in HIV/AIDS and his colleagues provided a slightly more detailed overview of the association between increased ARV use, decreasing viral loads and the number of new HIV diagnoses in British Columbia. Montaner report his group’s data on Thursday, February 18.
Unlike the somewhat fractured system of collecting real-world health care data in the United States, Montaner’s group was able to analyze centralized medical records for HIV testing, ARV prescription and viral load test results.
There has been a steady upswing in the number of annual HIV tests being conducted in British Columbia. In 1994, before programs were implemented to increase testing, 104,229 HIV tests were conducted. In 1996, 137,980 tests were conducted. In 2004 and 2008, 153,635 and 182,151 tests, respectively, were conducted.
From 1996—the year combination antiretroviral therapy became widely available—to 2003, new HIV diagnoses in British Columbia decreased from about 700 to 400 per year. This reduction was statistically significant. Between 2004 to present, there was a reduction from 450 to 380 per year. This difference was not statistically significant, meaning it could have been due to chance. There was, however, a significant reduction in the number of new HIV diagnoses among injection drug users during this time, from 150 in 2004 to 80 in 2008.
Montaner also reported increases in access to ARV therapy. In 2004, about 3,500 people were accessing ARV therapy. In 2009, about 5,500 people were being prescribed ARV treatment.
As for viral loads, about 1,500 HIV-positive individuals had levels in excess of 50,000 copies/mL in 2004. In 2009, only 800 people in British Columbia who knew they were HIV positive had viral loads above 50,000 copies. What’s more, the number of patients with viral loads below 500 increased steadily from 1996 to 2009.
Both Das-Douglas and Montaner noted a paradox in the collected data—increasing rates of sexually transmitted infections (STIs) such as syphilis, gonorrhea and chlamydia despite decreases in the number of new HIV cases. Typically, increases in STIs have been associated with increases in new HIV cases. Das-Douglas suggested one reason why the new HIV data might counter this assumption: It might be due to more sero-sorting among people living with HIV—the practice of engaging in sexual activity only with those with similar serostatuses.
Given certain limitations of both studies—notably their inabilities to prove a direct relationship between HIV treatment, viral loads and the number of new infections, but rather more basic associations between the collected data—Das-Douglas and Montaner were unable to draw firm conclusions. Yet, both believe increased ARV treatment options and coverage, as well as increased HIV status awareness, may have led to decreases in average community viral load and, with them, decreases in both the number of HIV diagnoses and the number of new HIV transmissions.
