Bayesian Spatiotemporal Projection of Chagas Disease Incidence in Brazil

Chagas Disease is a parasitic infection caused by the T. Cruzi parasite endemic to Central and South America and transmitted through contact with Triatomine insects, commonly known as "kissing bugs." Although the symptoms of Acute Chagas Disease (ACD) are nonspecific, untreated chronic infection can lead to heart disease, enlarged esophagus and colon, and stroke. Chagas disease has become increasingly rare owing to a series of public health interventions, including insect eradication campaigns in Brazil through the 1980s that considerably reduced the number of new acute cases. However, hundreds of new acute cases still are diagnosed annually, primarily in the states of Para, Amapa, and Acre. Moreover, the population in areas of high Chagas endemicity are changing: many areas are growing and becoming increasingly urban, whereas others are decreasing in population. We estimate the Incidence Rate (IR) for Acute Chagas disease over the period 2001-2019 in Brazil at the municipal level and investigate the variation of these rates with climatic factors. These estimates are used to project forward incidence of Acute Chagas Disease over the following decade 2020-2029. Modeling ACD presents numerous methodological challenges since incidence is rare, with extreme overdispersion of zero-case counts, and vectors exhibit a highly spatially- and temporally-clustered pattern. We use a spatially- and temporally-autoregressive small-area smoothing models to estimate the true latent risk in developing Acute Chagas Disease. The Bayesian model presented here involves spatio-temporal smoothing via a Zero-Inflated (Lambert 1992), Knorr-Held (2000)-Type spatio-temporal model with a BYM2 (Morris, 2019) spatial convolution to predict smoothed incidence rates of Chagas disease. As well, we include estimates of Brazils growing population and projected bioclimate to evaluate how climate and population change may affect ACD rates. We estimate that cases will continue to increase in the absence of control efforts, primarily driven by a growing peri-urban population in regions of Chagas endemicity.