Fine-Scale Mapping by Spatial Risk Distribution Modeling for Regional Malaria Endemicity and Its Implications under the Low-to-Moderate Transmission Setting in Western Cambodia.

Suguru Okami,Naohiko Kohtake,Luzia Helena Carvalho

doi:10.1371/journal.pone.0158737

Abstract

The disease burden of malaria has decreased as malaria elimination efforts progress. The mapping approach that uses spatial risk distribution modeling needs some adjustment and reinvestigation in accordance with situational changes. Here we applied a mathematical modeling approach for standardized morbidity ratio (SMR) calculated by annual parasite incidence using routinely aggregated surveillance reports, environmental data such as remote sensing data, and non-environmental anthropogenic data to create fine-scale spatial risk distribution maps of western Cambodia. Furthermore, we incorporated a combination of containment status indicators into the model to demonstrate spatial heterogeneities of the relationship between containment status and risks. The explanatory model was fitted to estimate the SMR of each area (adjusted Pearson correlation coefficient R2 = 0.774; Akaike information criterion AIC = 149.423). A Bayesian modeling framework was applied to estimate the uncertainty of the model and cross-scale predictions. Fine-scale maps were created by the spatial interpolation of estimated SMRs at each village. Compared with geocoded case data, corresponding predicted values showed conformity [Spearman’s rank correlation r = 0.662 in the inverse distance weighed interpolation and 0.645 in ordinal kriging (95% confidence intervals of 0.414–0.827 and 0.368–0.813, respectively), Welch’s t-test; Not significant]. The proposed approach successfully explained regional malaria risks and fine-scale risk maps were created under low-to-moderate malaria transmission settings where reinvestigations of existing risk modeling approaches were needed. Moreover, different representations of simulated outcomes of containment status indicators for respective areas provided useful insights for tailored interventional planning, considering regional malaria endemicity.

Highlights

Remaining issues and emerging challenges toward malaria eliminationDespite the many efforts over many years to contain and eliminate malaria, Malaria remains an important global health threat that still causes hundreds of thousands of deaths every year [1]
K where, oi is the observed number of cases in i area, ei is the expected number of cases in i area, nik is the population in k age group in i area, and Pk is the incidence of clinical cases in k age group in the reference population. ei was estimated by multiplying the population and reported incidence and aggregating them for each age group in 10 provinces in western Cambodia [41]
Within 5 km of villages, the absolute correlation values between environmental variables (NDVI, land surface water index (LSWI), and topographic wetness index (TWI)) extracted from surrounding circular buffers and EBSMR were highest at 5 km and at 1 km for normalized difference water index (NDWI) (Fig 2)

Summary

Introduction

Remaining issues and emerging challenges toward malaria eliminationDespite the many efforts over many years to contain and eliminate malaria, Malaria remains an important global health threat that still causes hundreds of thousands of deaths every year [1]. Remaining issues and emerging challenges toward malaria elimination. An increasing number of countries with low-to-moderate transmission areas have implemented actions to eliminate malaria from their entire territories [3]. A number of issues remain and new challenges are emerging in the efforts to eliminate malaria. The emergence of artemisinin resistance, which has been reported mostly in the Greater-Mekong subregions, is one of the new challenges [7]. A number of reports have emerged of delayed parasite clearance in patients in western Cambodia taking artemisinin [10,11,12,13]. One recent report showed that the artemisinin-resistant malaria parasite had the potential to infect vectors in other geographical regions [14]. Healthcare resources cannot be used inexhaustibly; identification of the target hotspots in malaria endemic areas, delivery of sufficient stockpiles of resources, and intimate support for local healthcare providers are essential, especially in remote endemic regions where accessibility cannot be retained over a whole year

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