• virological failure;
  • antiretroviral therapy;
  • virological suppression;
  • viral rebound


HIV-infected persons experience different patterns of viral suppression after initiating combination antiretroviral therapy (cART). The relationship between such differences and risk of virological failure after starting a new antiretroviral could help with patient monitoring strategies.


A total of 1827 patients on cART starting at least one new antiretroviral from 1 January 2000 while maintaining a suppressed viral load were included in the analysis. Poisson regression analysis identified factors predictive of virological failure after baseline in addition to traditional demographic variables. Baseline was defined as the date of starting new antiretrovirals.


Four hundred and fifty-one patients (24.7%) experienced virological failure, with an incidence rate (IR) of 7.3 per 100 person-years of follow-up (PYFU) [95% confidence interval (CI) 6.7–8.0]. After adjustment, patients who had rebounded in the year prior to baseline had a 2.4-times higher rate of virological failure after baseline (95% CI 1.77–3.26; P<.0001), while there was no increased incidence in patients whose last viral rebound was >3 years prior to baseline [Incidence rate ratio (IRR) 1.06; 95% CI 0.75–1.50; P=0.73] compared with patients who had never virally rebounded. Patients had an 86% (95% CI 1.36–2.55; P<.0001), 53% (95% CI 1.06–2.04; P=0.02) and 5% (95% CI 0.80–1.38; P=0.72) higher virological failure rate after baseline if they were virally suppressed <50%, 50–70% and 70–90% of the time they were on cART prior to baseline, respectively, compared with those virally suppressed >90% of the time.


Intensive monitoring after a treatment switch is required in patients who have rebounded recently or have a low percentage of time suppressed while on cART. Consideration should be given to increasing the provision of adherence counselling.