Claudie Laprise of the University of Montreal, who worked in close collaboration with doctors from the Clinique medicale du Quartier Latin de Montreal, said their study was based on data from the files of 1,860 people living with HIV over 12 years. Nearly 94 percent of the patients were men.
The prognosis for people with HIV has considerable improved since the advent of anti-retroviral therapy in 1996, which acts by reducing the presence of the retrovirus in the blood of infected people. This maintains the immune functions required to prevent the disease from progressing to AIDS. From a clinical point of view, the viral load test measures the activity of HIV in the patient and the effectiveness of the anti-retroviral therapy.
The goal of treatment is to keep the viral load below the detection limit, which is about 50 copies of viral RNA/milliliter.
Despite treatment, patients sometimes show persistent low viral load during medical followup, from 50 to 1,000 copies/ml, for a number of months. The higher the persistent viral loads, the higher the patients are at risk of developing virologic failure.
"Virologic failure, defined in this study as a viral load above 1,000 copies/ml of viral RNA in the blood, is to be avoided, not least because it shows the progression of the disease," Laprise said in a statement.
Laprise's findings confirmed the risk of virologic failure is a function of persistent viral load. Thus, a patient with a persistent viral load between 500 and 999 copies/ml after a six-month followup runs a five times higher risk of virologic failure compared with patients whose viral load is undetectable, the study found.
However, a persistent low viral load -- 50 to 199 copies/ml -- doubles this risk as much as an "average" persistent viral load -- 200 to 499 copies/ml, the study said.
"This result surprised us because we did not believe that a load as low as 50 to 199 copies/ml after six months could result in a significant risk of virologic failure," Laprise said.