Test-and-treat not enough to control HIV epidemic in the US

Only 19% of HIV-positive individuals in the US have an undetectable viral load, and this means that a “test-and-treat” strategy by itself will not be enough to control the country’s HIV epidemic, investigators argue in the March 15^th edition of Clinical Infectious Diseases.

Late diagnosis, low levels of referral and retention in specialist HIV care, and sub-optimal adherence to antiretroviral therapy all undermined the potential for test-and-treat to eradicate transmission of the virus.

“This review demonstrates that incomplete engagement in HIV care is common in the United States and that incompletely engaged individuals account for the largest proportion of HIV-infected individuals with detectable viremia,” comment the investigators, who believe their findings “have direct implications for test-and-treat programs, because disengaged individuals continue to contribute to the ongoing transmission of HIV infection.”

The investigators also estimated that even in the best-case scenarios over a third of HIV-positive individuals in the US would still have a detectable viral load and therefore be at risk of transmitting the virus to others.

Prof. Joep Lange in his accompanying editorial described the small proportion of US patients with an undetectable viral load as “shocking.” He argued that “combination prevention” was the best hope of controlling the epidemic.

Improvements in HIV treatment and care mean that many HIV-positive patients now have a realistic hope of a normal prognosis. To have the best hope of this outcome individuals need to have their infection diagnosed early, utilise specialist HIV care services, initiate antiretroviral therapy at the optimum time, and have high levels of adherence to their treatment.

Another advantage of antiretroviral therapy is its impact on infectiousness. Patients who have an undetectable viral load when taking HIV treatment are at very low risk of transmitting the virus to others. Therefore, a test-and-treat strategy has been advocated as a way of not only improving the life-expectancy of patients already infected with the virus, but also as a way of controlling the epidemic.

Investigators from the US wished to see if this approach to prevention was realistic.

There are approximately 1.1 million HIV-infected individuals in the US, and HIV incidence in the country is steady at around 56,000 new infections each year.

Rates of HIV testing in the US have increased in recent year, but approximately a fifth of all infections are still undiagnosed. The investigators note that undiagnosed individuals “cannot engage in treatment that reduces morbidity and mortality, may participate more often in high-risk HIV transmission behavior, and have a higher risk of transmitting HIV to others than do those who are aware of their HIV infection.”

Failure to link patients with specialist care after their diagnosis is also common. The investigators found that 25% of newly-diagnosed individuals were not successfully linked to HIV care within six-twelve months of their diagnosis, and between 10%-20% of patients remained unengaged in care three to five years after their diagnosis.

Rates of retention in care were also found to be far from perfect. “50% of known HIV-infected individuals are not engaged in regular HIV care,” comment the investigators, adding “poor engagement in care is associated with poor health outcomes, including increased mortality. In addition, these individuals contribute to ongoing transmission in the community.”

But being in care did not guarantee that patients would receive optimum therapy. The investigators calculated that on the basis of current guidelines, 80% of in-care patients were eligible for antiretroviral therapy. However, approximately 27% of individuals either declined this treatment or failed to initiate it for some other reason.

Moreover, results from cohort studies suggest that between 4% - 6% of patients stop taking their HIV therapy each year.

Newer anti-HIV drugs are powerful, have generally mild side-effect profiles, and forgiving adherence requirements. Nevertheless, the researchers found that between 13% - 22% of patients taking antiretroviral therapy still have a detectable viral load and are at risk of transmitting the virus to others.

After taking into account all these factors the investigators calculated that only 210,000 HIV-positive patients in the US have an undetectable viral load. These patients constitute just 19% of the HIV-infected population in the US.

“With > 80% of HIV-infected individuals in the United States having detectable HIV viremia, it is not surprising that the incidence of HIV infection has not decreased in the United States despite almost 15 years of widespread access to antiretroviral therapy,” comment the investigators.

However, they also found that even in a best-case scenario, a test-and-treat strategy would not be sufficient to control the HIV epidemic.

They write: “Diagnosis of 90% of HIV infections, achievement of 90% engagement in care, treatment of 90% of engaged individuals, and suppression of viremia in 90% of treated individuals could lead to considerable improvements in the proportion of HIV-infected individuals in the United States with undetectable viral loads. However, even in this ideal scenario, approximately 34% of HIV-infected individuals will remain viremic, with the potential to spread HIV infection to others.”

The researchers therefore conclude, “complete eradication of HIV infection through test-and-treat programs is unlikely.”

Nevertheless, they believe that “incremental improvements in methods to overcome the greatest care challenges today in the United States – undiagnosed HIV infection and inadequate engagement in HIV care – will improve the care of HIV-infected populations and decrease the incidence of HIV infection in the future.”

In his accompanying editorial, Prof. Lange suggests that the study shows the limitations of a test-and-treat approach.

He writes: “It is unlikely that ‘test and treat’ strategies by themselves, even if vigorously and comprehensively pursued, will be sufficient to end the epidemic. It should be clear that ‘combination HIV prevention’, using a mix of available prevention tools, including ‘test and treat’ strategies, in a context-specific manner based on knowledge about local, national, and regional epidemics, is the way forward.”