Impact of alcohol disorder and the use of illicit drugs on tuberculosis treatment outcomes: a retrospective cohort study.

BACKGROUND: Alcohol and illicit drugs are associated with the discontinuation of tuberculosis (TB) treatment and can compromise the immune system. We estimated the impact of alcohol disorder and the use of illicit drug on TB treatment outcomes, considering the interaction of both substances in patients from São Paulo state, Brazil. METHODS: This is a retrospective cohort of patients diagnosed with TB from 2011 to 2015. We estimated the relative risk (RR) of an unsuccessful outcome associated with alcohol disorder, use of illicit drugs and their interaction using a multiple regression model. We used the adjusted RR to estimate the population attributable fraction. RESULTS: Out of a total 77,212 TB patients, 22.2% used at least one of the substances of interest during treatment, while 17% presented an unsuccessful outcome of TB treatment. Compared with no exposure to any substance, alcohol disorder alone (adjusted RR: 1.48; 95% CI: 1.4-1.56), drug use alone (adjusted RR: 2.1; 95% CI: 1.98-2.21) and exposure to both substances (adjusted RR: 2.09; 95% CI: 1.97-2.21) were all associated with a higher risk of an unsuccessful outcome. The adjusted RR of an unsuccessful outcome for people exposed to both substances was 32.7% (95% CI: 26.8-38.2%) and 15.8% (95% CI: 11.5-20.1%) lower than expected on the multiplicative and additive scales respectively. Among all TB patients, 15.8% (95% CI: 15-16.5%) of unsuccessful outcomes was attributable to those exposures. CONCLUSIONS: We identified a negative interaction between alcohol disorder and the use of illicit drugs on TB treatment outcomes. Despite this, interventions to reduce substance use in TB patients could have a meaningful contribution to preventing unsuccessful treatment outcomes.