Community viral load as prevention

Das M. PLoS One. 2010;5:e11068

In this Ask the Experts feature, Moupali Das, MD, discusses what is meant by the term ‘community viral load’ as a prevention strategy in HIV.

What is meant by the term ‘community viral load’?

Community viral load (CVL) is a general term for a family of measures that estimate the cumulative burden of viremia in a community. It is most often measured as the mean of the most recent viral load of all individuals living with HIV in a particular jurisdiction during a particular time period, usually annually. The mean CVL allows comparisons between neighborhoods or among subpopulations. There are other measures such as the maximum or peak community viral load, which is the mean of each individual’s highest viral load in a year. This would be the most conservative estimate of viremic burden. The total community viral load is the total of all the viral loads of all the individuals in a community — this measure is driven both by the number of people living with H IV and the cumulative viremia.

We hypothesized that expanded diagnosis of HIV and increased uptake of antiretroviral therapy would be associated with decreases in CVL over time in San Francisco. We further posited that decreases in CVL would be associated with reductions in new HIV diagnoses in San Francisco. We have demonstrated that, indeed, decreases in CVL are associated with reductions in new diagnoses.

We have also shown that no matter how you measure CVL, decreases in CVL over time are associated with reductions in new HIV diagnoses.

Thus, we believe that CVL is a useful measure of both the effectiveness of HIV prevention interventions and antiretroviral treatment, at the population level. Monitoring trends in CVL and disparities in CVL can help public health officials decide where to direct resources and evaluate the effectiveness of high-impact combination HIV prevention and treatment programs.

How do the HPTN 052 results affect your thinking on a community-wide implementation strategy?

HPTN 052 results are consistent with our understanding of the biology of HIV transmission. We now have proof of concept that “treatment is prevention” in all modes of HIV transmission. There are few diseases where treatment so markedly transforms an individual’s life expectancy and quality of life. We are hopeful that expanded HIV screening and uptake of ART on a population or community-wide level will transform and turn the tide of the epidemic.

Some are concerned that you won’t be able to find the very people most likely to be transmitting HIV, including those with acute HIV infection. How do you respond?

The median CD4 at diagnosis in the United States remains below 200; we must do better in diagnosing all HIV infections, acute and chronic. It is true that acutely infected individuals are more likely to transmit HIV due to both biology (high viral load) and behavior (unaware of positive status and, therefore, possibly riskier than if aware). We could certainly stand to improve our ability to diagnose acutely infected individuals by reinforcing education with emergency room physicians, primary care physicians and the non-infectious disease specialists who are most likely to see individuals as they present with the viral symptoms of acute retroviral syndrome.

We can also improve awareness among the community at-risk about the signs and symptoms of acute HIV infection. There have been some innovative and edgy campaigns proposed to this end: “Don’t screw with the flu.” But we must do better in diagnosing acutely infected individuals, as well as find those chronically infected with effective strategies such as routine HIV screening in medical settings, if we are to turn the tide in the epidemic.

There is growing evidence that although HIV incidence may be declining, this may be from serosorting as much as from treatment. There is a growing rate of syphilis and other STIs. Don’t we run the risk of an HIV-centered approach such as CVL that doesn’t deal with other infections?

HIV and other STIs are all transmitted through unprotected sex. The practice of HIV-positive serosorting, where HIV-positive individuals have unprotected sex with other HIV-positive individuals, has been hypothesized as one of the primary reasons why rates of syphilis and rectal gonorrhea are increasing while HIV incidence has declined or stayed stable.

It is difficult to tease apart the relative contributions of increasing rates of virologic suppression and positive serosorting toward declining or stabilized HIV incidence. Negative serosorting is the highest risk for acquisition of HIV, as one individual who is acutely infected and unaware of his/her HIV-positive status can have a very significant impact in terms of chains of transmission. We must continue to encourage individuals to have safer sex and reduce sexual risk behavior to reduce the acquisition and transmission of STIs and increasingly hepatitis C among men who have sex with men.

However, we must acknowledge and incorporate the growing body of evidence that transmission is less likely from HIV-positive individuals with an undetectable viral load in our public health messages. For those who are unable to consistently practice safer sex, for example, discordant monogamous couples, viral suppression in the HIV-positive partner may be an effective harm reduction strategy. This is not to say that we should dispense with our public health messages regarding sexual risk reduction for all STIs.

A comprehensive sexual health approach that promotes wellness and prevention of all STIs is the soundest public health strategy.

Moupali Das, MD, MPH, is the director of research and policy in the HIV Prevention Section at the San Francisco Department of Public Health. Disclosure: Dr. Das reports no relevant financial disclosures.

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