Abstract:
Malaria is a leading cause of morbidity and one of the most targeted communicable diseases.
Malaria transmission varies in space and time. Understanding and extracting trends and
noticeable patterns from district-level malaria surveillance data is crucial for achieving malaria
reduction targets. The interplay of climate and environmental variability with malaria
epidemiology is not explored. This study aimed to examine spatio-temporal patterns and trends of
malaria epidemic by accounting for climate variabilities. Moreover the study strives to detect
space-time clustering and develop a spatio-temporal predictive model for malaria transmission in
the Amhara region, Ethiopia. The monthly malaria case incidence and environmental data were
collected from Amhara Public Health Institute, NASA, CHIRPS and World Global Climate
Databases. We have employed advanced statistical models such as parametric and nonparametric
spatio-temporal trend models, Bayesian generalized Poisson model, Kulldorff’s retrospective
space-time scan statistic, spatio-temporal generalized additive models, classification and
regression training for spatio-temporal data (CAST), and Bayesian spatio-temporal predictive
models. The linear parametric spatio-temporal trend estimate revealed a decreasing trend, and
differential trends indicate that districts have substantial variations in their malaria transmission
scenarios; meanwhile, most of the town districts have a lower reducing rate of malaria incidence.
However, the thin-plate regression estimate shows a decreased trend between 2012 and 2016, and
a drastic change has occurred since 2017. Malaria transmission is highly seasonal and modeled
using cyclic cubic regression spline and shows that higher malaria cases occurred between
September and December, with a higher seasonal index in October and December. Climate and
environmental variability had a complex interplay with malaria transmission. The average altitude
of districts, monthly average minimum temperature, monthly total rainfall, and coverage of at least
one long-lasting insecticide net (LLINs) had significant effects on malaria transmission. However,
the non-linear effects of climate variables revealed that the effects of climate variabilities were not
homogenous across all the ranges of its values. Clustering of districts with a higher malaria risk
was detected using Kulldorff’s retrospective space-time scan statistics, and the most likely space time cluster was seen in the western and northwestern parts of the region and occurred between
July 2012 and December 2013. The spatio-temporal predictive model was performed using
nonparametric and parametric supervised machine learning predictive models.
Key words: Bayesian approach; Climate variability; Generalized additive models; Malaria
surveillance; Predictive model; Spatial risk; Spatio-temporal; Spatio-temporal clustering.