Measuring the proportion of people with an undetectable viral load may be lulling health policymakers into a false sense of security in their efforts to control HIV transmission through comprehensive treatment, according to a new study from South Africa.
Undetectable viral load has been adopted “as a proxy for ART [antiretroviral therapy] program effectiveness” as a result of the UNAIDS 90-90-90 target, which aims for 90% of people living with HIV diagnosed, 90% of people with diagnosed HIV infection to be on treatment and 90% of people on antiretroviral therapy to have undetectable viral load by 2020. The undetectable viral load target is often referred to as the ‘third 90’.
Progress towards this target leads to the assumption that the number of people with HIV who have a detectable viral load, and who might pass on HIV, is shrinking.
But, say researchers from the Africa Health Research Institute, Durban, in settings with very high HIV prevalence, focusing on the proportion of people with HIV who still have detectable viral load gives a false sense of how much potential for HIV transmission exists in the population. Instead, health policymakers need to focus on the proportion of the entire population that has detectable viral load, so as to take into account the growth of the population living with HIV over time
Research by the same group due to be published shortly has shown that the risk of acquiring HIV is strongly associated with the proportion of the entire population that has detectable viral load, but not the proportion of people with HIV with a detectable viral load.
Looking at the Umkhanyakude district in the South African province of KwaZulu-Natal, which has a population of around 90,000 people, the researchers show that between 2011 and 2014 the proportion of people living with HIV who had detectable viral load fell markedly, but when they looked at the entire population of the district, there was almost no change in the proportion with a detectable viral load.
Umkhanyakude district has extremely high HIV incidence – around 6% of young women aged 24 were becoming infected each year at the peak of HIV transmission between 2004 and 2011 – and 28.7% of men and women aged 15 to 54 were HIV positive by 2010. HIV treatment began to become available in 2004 and eligibility for treatment was expanded to everyone with CD4 counts below 350 cells/mm3 in 2011 and by 2013, 40% of people with HIV were taking antiretroviral treatment.
To find out whether measuring the proportion of people with HIV having undetectable viral load gives an accurate picture of the risk of HIV transmission in a population, Africa Health Research Institute measured viral load in everyone who tested HIV positive in household surveillance surveys in the district in 2011, 2013 and 2014. The survey identified 5368 people with HIV aged 15 to 64 years but it was necessary to exclude approximately 10% of samples that provided an insufficient quantity of dried blood for viral load testing, leaving 4991 unique participants.
The prevalence of detectable viral load among people with HIV fell from 73.7% in 2011 to 59.9% in 2014, implying that 40.1% of all people with HIV had undetectable viral load at this time.
However, during the same period, and partly as a result of the expansion of HIV treatment eligibility and reductions in mortality, but also due to continuing high HIV incidence, HIV prevalence increased from 26.7% in 2011 to 32.3% in 2015.
So, when measuring the prevalence of detectable viremia in the population as a whole, the researchers found little or no decline in the proportion of the population of the entire district that had a detectable viral load. In 2011 18.8% of the population had a detectable viral load, and in 2014 17.9% had a detectable viral load, a reduction of 0.92%. By 2014, the chance that a member of the population would have undetectable viral load had fallen by only 9% compared to 2011 (odds ratio 0.91, 95% CI 0.85-0.97, p=0.009).
Furthermore, the proportion of men in the district with detectable viral load actually rose, from 14.6% in 2011 to 16.2% in 2014.
The investigators warn that although measuring the proportion of people with HIV with detectable viral load “may reflect a community’s exposure to ART, it may not tell us enough about the potential for HIV transmission within the general population.” They warn that countries should monitor and report the prevalence of detectable viremia among all adults as a more reliable proxy for HIV transmission risk.
By Keith Alcorn
Vandormael A et al. Longitudinal trends in the prevalence of detectable HIV viremia: Population-based evidence from rural Kwazulu Natal, South Africa. Clin Infect Dis, advance online publication, 2017.