Objective This study examines the proportions and causes of virological failure after one year of antiretroviral therapy (ART) among people living with HIV (PLHIV) in Vietnam. It also evaluates the positive predictive value (PPV) of immunological criteria to detect treatment failure.

Method A retrospective cohort of 3449 people with HIV who started ART between 1 January 2005 and 31 December 2009 in 13 outpatient clinics in Vietnam was studied. Multivariate logistic regression modeling was used to calculate crude and adjusted ORs and 95% CIs for associations between patient characteristics and virological failure.

Results An estimated 6.5% (226/3449) of HIV patients in the participating clinics in Vietnam had confirmed virological failure one year after the start of ART. After adjusting for other factors, patients with a baseline CD4 count of 50–100 cells/mm³ and 101–200 cells/mm³ were statistically significantly less likely to have virological failure, compared to those with a baseline CD4 count lower than 50 cells/mm³ (OR=0.61, 95% CI 0.23–0.89; and OR=0.43, 0.18–0.78, respectively). In contrast, patients with a history of injecting drug use were statistically significantly more likely to have viraemia than otherwise (OR=1.32, 1.16–1.67). The PPV of the WHO immunological criteria was 60.1% (57.1–69.3%).

Conclusions Routine viral load tests should be conducted early to detect virological failure and prevent unnecessary changes to second-line treatments. To improve treatment outcomes, timely ART initiation and adherence to treatment among those with history of injecting drug use should be promoted.