Adherence to anti-Tuberculosis treatment during the COVID-19 pandemic: a single-centre, retrospective analysis

Introduction: Adherence to tuberculosis (TB) treatment is essential to achieve favourable outcomes, yet difficult to evaluate. Our study evaluates adherence using pharmacy refill data, and assesses COVID-19 pandemic's impact on TB care cascade. Materials and methods: We retrospectively analysed patients diagnosed with TB at our unit in Florence (Italy) between January 2020 and December 2023. Adherence was measured using the Proportion of Days Covered (PDC) and compared with self-reported adherence and attendance at follow-up visits. PDC was calculated for the intensive (PDC1) and continuation phase (PDC2), and overall treatment (PDC). Data were compared between the pandemic (2020–2021) and post-pandemic (2022–2023) periods. Results: Among 135 subjects, 73.3% had a favourable outcome. Lost-to-follow-up patients (14.8%) more frequently included transgender, foreign-born and HIV-coinfected individuals. Mean PDC was 0.67; 74.5% of patients exhibited PDC<1. Adherence was lower during the continuation phase (PDC2 = 0.84) compared to the intensive phase (PDC1 = 0.94). PDC and PDC1 were significantly lower during the pandemic. Non-adherent patients reported more missed doses and skipped appointments. Conclusions: PDC is a simple, cost-effective tool to monitor adherence, that correlates well with self-reported adherence and follow-up visits attendance. TB treatment adherence remains suboptimal and the COVID-19 pandemic further exacerbated barriers to care, particularly among vulnerable populations such as migrants.