Failure to return pillbox is a predictor of being lost to follow-up among people living with HIV on antiretroviral therapy in rural Tanzania

Objectives: Pill count is used to assess drug adherence in people living with HIV (PLHIV). Carrying a pillbox is associated with fear of concealment and stigma and might indicate poor adherence and predict someone who will be lost to follow-up (LTFU). We therefore assessed the association between pillbox return and being LTFU in rural Tanzania. Methods: This is a nested study of the Kilombero and Ulanga Antiretroviral Cohort (KIULARCO). We included PLHIV aged ≥ 18 years enrolled in KIULARCO between January 2013 and March 2019 with follow-up through January 2020, who were on antiretroviral treatment (ART) for ≥ 6 months. Baseline was defined as the latest ART initiation or KIULARCO enrolment. We determined the association between time-dependent failed pillbox return updated at every visit and LTFU using Kaplan–Meier estimation and Cox models. Results: Among 2552 PLHIV included in the study, 1735 (68.0%) were female, 959 (40.3%) had a WHO stage III/IV and 1487 (66.4%) had a CD4 cell count < 350 cells/µL. The median age was 38.4 years [interquartile range (IQR): 31.7–46.2]. During a median follow-up of 33.1 months (IQR: 17.5–52.4), 909 (35.6%) participants were LTFU, 43 (1.7%) died and 194 (7.6%) had transferred to another clinic. The probability of being LTFU was higher among PLHIV with failed pillbox return than among those who returned their pillbox [30.0%, 95% confidence interval (CI): 26.8–33.2% vs. 19.4%, 95% CI: 17.4–21.6%, respectively, at 24 months (hazard ratio = 1.67, 95% CI: 1.46–1.90; p < 0.001)]. Conclusions: Failed pillbox return was associated with a higher risk of being LTFU and could be used as a simple tool to identify PLHIV for appropriate interventions to reduce their chance of being LTFU.