Spatial clustering, social vulnerability and risk of leprosy in an endemic area in Northeast Brazil: an ecological study

[[[ Background: ]]] Despite the global decline in the detection of leprosy cases, its incidence has remained unchanged in certain settings and requires the determination of the factors linked to its persistence. We examined the spatial and space-time distribution of leprosy and the influence of social vulnerability on the occurrence of the disease in an endemic area of Northeast Brazil. [[[ Methods: ]]] We performed an ecological study of all leprosy cases reported by Sergipe state, Northeast Brazil from 2001 to 2015, to examine the association of the Social Vulnerability Index and the prevalence and persistence of leprosy among the State’s municipalities. Socio-economic and leprosy surveillance information was collected from the Brazilian information systems, and a Bayesian empirical local model was used to identify fluctuations of the indicators. Spatial and space-time clusters were identified using scan spatial statistic tests and to measure the municipalities’ relative risk of leprosy. [[[ Results: ]]] Leprosy clusters and burden of disease had a strong statistical association with the municipalities’ Social Vulnerability Index. Municipalities with a high social vulnerability had higher leprosy incidence, multibacillary leprosy and newly diagnosed cases with grade 2 disability than areas with low social vulnerability. [[[ Conclusion: ]]] Social vulnerability is strongly associated with leprosy transmission and maintenance of disease incidence. Leprosy control programmes should be targeted to the populations with high social vulnerability.