Risk clusters of Schistosoma mansoni infection in an endemic state of Brazil: space-time modelling and association with socio-economic and environmental factors

Background: We analysed the spatial distribution and the socio-economic and environmental factors (SEFs) associated with Schistosoma mansoni infection in the state of Alagoas, an important tourist area in northeastern Brazil. Methods: We conducted an ecological time-series study (2007-2016) on schistosomiasis cases and SEFs. We evaluated the temporal trends of schistosomiasis cases (annual percentage change [APC]) and their correlation with SEFs. Spatial analysis maps were built using QGIS and TerraView software. Results: We observed that 4.9% of the municipalities had a high prevalence of S. mansoni infection and were located mainly in the coastal strip of Alagoas state. The positivity rate for schistosomiasis decreased during the period (8.1% in 2007 to 4.9% in 2016; APC=-5.71). There was a reduction in the number of tests performed (APC=-5.05). There was a negative correlation between S. mansoni infection and the municipal human development index (rho=-0.34) and schooling rate (rho=-0.24). The main species of snail was Biomphalaria glabrata (94.79%), but Biomphalaria straminea showed a higher percentage of S. mansoni detection (10.11%). Lastly, Biomphalaria tenagophila specimens were identified for the first time in Alagoas (n=28). Conclusions: Despite a reduction in the number of cases, intestinal schistosomiasis still represents a serious public health concern in Alagoas. It urgently requires planning and improvements in diagnosis, prevention programs and the state's socio-economic indicators.