Underlying mechanisms of leprosy recurrence in the Western Amazon: a retrospective cohort study

Background The multidrug therapy (MDT) for leprosy treatment adopted by Brazil in the 1990s was important for reducing leprosy in the country; however, recurrent cases remained problematic. Mechanisms involved in leprosy recurrence are heterogeneous and can be sorted into three groups: insufficient therapy, bacillary persistence and new infections. This study aimed to analyse the time interval of leprosy recurrence in relation to the therapeutic scheme in the state of Acre. The hypotheses were as follows: 1) treatments (a) rifampicin, ofloxacin and minocycline (ROM) and (b) dapsone (DDS) have a short leprosy recurrence time, 2) treatments based on MDT have a long leprosy recurrence time, 3) there is a dose-response relationship between MDT and the time interval between leprosy episodes. Methods This retrospective cohort study included 201 patients with a second episode of clinical leprosy at the reference centers for leprosy control in the state of Acre. Exposure was the type of therapeutic scheme as follows: 1) ROM, 2) DDS, 3) MDT 0–9 doses , 4) MDT 10–19 doses , 5) MDT 20–29 doses , and 6) MDT 30+ doses . Outcome was the time interval between release from treatment and a diagnosis of a recurrent leprosy case. Incidence rate ratios and relative risk Poisson regressions adjusted by age and sex were calculated with 95% confidence intervals. Results The 201 patients studied during this retrospective follow-up resulted in a total of 224 cases of recurrent leprosy. Incidence rate ratios within this therapeutic scheme were as follows: 3.3 (2.39, 4.2; ROM/MDT 30+ ), 1.12 (0.33, 1.92; DDS/MDT 30+ ), 2.17 (1.39, 2.94; MDT 0–9 /MDT 30+ ), 1.94 (1.13, 2.75; MDT 10–19 /MDT 30+ ) and 1.26 (0.47, 2.05; MDT 20–29 /MDT 30+ ). Relative risk Poisson regressions showed a protective effect of MDT 30+ in comparison with ROM (0.22; 0.07, 0.72), MDT 0–9 (0.42; 0.21, 0.85), and MDT 10–19 (0.44; 0.21, 0.92). No differences among MDT 30+ and DDS (0.71; 0.36, 1.41) and MDT 20–29 (0.76; 0.38, 1.49) were observed. Conclusions New infection is an important—yet neglected—mechanism in leprosy recurrence in the state of Acre and can challenge the leprosy elimination plan in Brazil. MDT with few doses might be associated with leprosy recurrence due to insufficient therapy or bacillary persistence.