We know that when persons are infected with HIV and have not been diagnosed, the virus replicates silently in their bodies for several years. During this time, their immune systems are being damaged and they are very likely to spread the virus to others since they are unaware of their infection. That is why the National HIV AIDS Strategy has identified a specific target for increasing the number of persons who have their HIV infection diagnosed in a timely manner: “By 2015, increase from 79% to 90% the percentage of people living with HIV who know their serostatus (from 948,000 to 1,080,000).”

If you are diagnosed with HIV, your health care provider will evaluate the state of your infection by ordering a number of laboratory tests, including a viral load (VL) test. Viral load is the clinical laboratory test that gauges the level of viral replication by measuring the actual amount of viral genetic material present in a person’s bloodstream. When the viral load is high, it indicates that the virus is actively reproducing—not a good thing. Generally speaking, the higher the viral load, the greater the potential damage to the immune system—and the greater the likelihood of transmitting the virus through unsafe sex or needle-sharing activities. But persons who are on effective antiretroviral (ARV) treatment will have very low viral loads—often so low that they are “undetectable” at the current level of testing sensitivity. Because having an undetectable viral load is one important measure of quality HIV care, it, too, has been identified in the NHAS as a target. Under the goal of “Reducing HIV-Related Disparities,” we are asked to increase, by 20%, the proportion of HIV-diagnosed gay and bisexual men, Blacks, and Latinos who have undetectable viral loads.

Without a doubt, viral load is a very important tool in the clinical management of HIV disease. But now, there is a newly emerging way to use viral load as a population measure: community viral load (CVL). Here’s how it works. We can group individual viral load measurements from various groups who have been diagnosed and are receiving HIV care, for example, African American women, Latino men who have sex with men, transgender women, or White injection drug users. Then we can compare the average viral load for each of these groups to identify disparities across the groups. Since the goal is for all persons who are under HIV care to have an undetectable viral load, if a neighborhood or a community or a particular group has a higher CVL, it indicates a need to intervene. An elevated CVL can mean that persons are being diagnosed very late in the course of their infection, or that they are not receiving timely referral into medical care or even that they might require additional adherence counseling in order to maintain consistent ARV use.

Given its emerging importance as an aggregate measure of HIV programmatic efforts, we are seeing more and more references to CVL. At this week's CROI meeting in Boston, researchers from New York, San Francisco, Baltimore, and Washington, DC all shared information about how they are using CVL to monitor access to diagnosis, care and treatment for HIV infection. In San Francisco, reductions in community viral load have even been associated with decreases in newly diagnosed and reported HIV infections. Public health leaders at the CDC and elsewhere are working to improve the capacity of state and local health departments to be able to monitor this increasingly useful population measure.