As cases of visceral leishmaniasis (VL) dwindle, there is justification to pursue a finer scale than the sub-district ("block") for monitoring the progress of elimination in India. Low incidence projections across broad regions of unevenly-distributed communities are difficult to act upon, and focal pockets of incidence cannot be overlooked if the goal is to avoid resurgence and sustain equitable elimination. However, maintaining consistent surveillance at a fine scale is difficult to justify in a low-resource elimination setting and not sustainable in the long-term.
This work analyses village-level incidence across the whole of Bihar. Spatial auto-correlation in observed incidence and associations with local environmental conditions are explored, and a statistical disaggregation approach is evaluated to infer village-level variation from routine block-level data. We found that the approach did not estimate village-level incidence more accurately than a baseline assumption of block-homogenous incidence, and that this inaccuracy did not appear to be due to non-linear or interacting covariate effects. We suggest that mechanisms of the current surveillance system may limit the predictability of observed village-level incidence, and that this should be a consideration when interpreting the output of disaggregation models.
Spatial autocorrelation is evident on a block-level but appears weak between neighbouring villages within individual blocks, suggesting that an important transmission mechanism may act at a longer range (for example due to population movement). Increasing the range of reactive interventions to neighbouring villages may therefore not improve efficacy, however increased routine surveillance and treatment among mobile population groups may be beneficial in reducing the risk of reintroduction into previously unaffected villages.