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14% of HIV patients have minority drug resistant variants

Researchers from the AIDS Research Institute (IrsiCaixa) participated in a study led by Harvard University that indicates that some HIV-positive individuals have a one of variety of strains that are resistant to antiretroviral drugs and are not detectable by routine resistance testing

STAFF | APRIL 6TH, 2011

Every HIV patient is infected with the thousand different viruses called viral variants. Some variants are more common than others and sometimes they incorporate mutations that cause drug resistance, i.e. they make treatment less effective. Before a patient starts antiretroviral treatment, doctors always verify that the virus is not resistant to that medication, by the so-called resistance testing.

Routine resistance testing, however, only detects the most common viral variants, i.e. those that are present in more than 15% -20% of the viruses infecting each patient. But the treatment also fails in some patients who apparently have no resistant variants.

A study led by Harvard University and involving researchers from the AIDS Research Institute (IrsiCaixa) has demonstrated that in some cases treatment fails because patients have minority resistant variants not detected by standard methods. The presence of these minority variants of HIV resistant to drugs doubles the risk of virologic failure.

The presence of these minority variants doubles the risk of treatment failure The discovery has been published on April 6 in the Journal of the American Medical Association. The study involved Roger Paredes, a researcher at IrsiCaixa, which is supported by La Caixa Bank’s Social Welfare program and the Department of Health of the Generalitat of Catalonia and the HIV Unit of the Hospital Germans Trias i Pujol in Badalona. Various other international research centers like the University of Zurich, Yale University and University College London also participated in the study.

New diagnostic techniques

The study analyzed samples from a total of 985 patients which, according to standard resistance tests, had no resistant variants. The researchers used massive sequencing techniques to detect virus variants present in up to 0.1% of the HIV virus in the body. With these ultra-sensitive tests, they have found that 14% of patients who apparently had no resistant variants, in fact, had resistant minority variants that are not detected by standard tests.

In the group of patients without resistance of any kind, the treatment failed in 15% of cases, while in patients with minority resistant variants, the failure rate was 35%. Therefore, the study shows that the presence of minority resistant variants doubles the risk that treatment does not work. This risk is equivalent to not taking the medication properly.

The new test could prevent treatment failure in one of every 11 patients The detection of these minority resistant variants has been made possible by the application of tools for the genomic sequencing of viruses in clinical diagnosis. These tools can perform more precise tests for resistance and thereby improve the diagnosis and treatment of seropositive patients. If these tests could be used widespread, they could prevent treatment failure in one out of every 11 patients.

The researchers hope that this form of diagnosis, which is currently still in testing, can be applied to all HIV-positive patients within two years.

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