Quantifying spatial heterogeneity of malaria in the endemic Papua region of Indonesia: analysis of epidemiological surveillance data
Authors: Fadilah Ihsan , Djaafara Bimandra A. , Lestari Karina D. , Fajariyani Sri Budi , Sunandar Edi , Makamur Billy Graham , Wopari Berry , Mabui Silas , Ekawati Lenny L. , Sagara Rahmat , Lina Rosa N. , Argana Guntur , Ginting Desriana E. , Sumiwi Maria Endang , Laihad Ferdinand J. , Mueller Ivo , McVernon Jodie , Baird J. Kevin , Surendra Henry , Elyazar Iqbal R. F. 
Published: April 2022

Background

As control efforts progress towards elimination, malaria is likely to become more spatially concentrated in few local areas. The purpose of this study was to quantify and characterise spatial heterogeneity in malaria transmission-intensity across highly endemic Indonesian Papua.

Methods

We analysed individual-level malaria surveillance data for nearly half a million cases (2019–2020) reported in the Papua and West Papua provinces and adapted the Gini index approach to quantify spatial heterogeneity at the district and health-unit levels. We showed malaria incidence trends and the spatial and temporal distribution of sociodemographic characteristics and aetiological parasites among cases.

Findings

While Papua province accounted for the majority of malaria cases reported in the region and had seen a rise in transmission since 2015, West Papua province had maintained a comparatively low incidence. We observed that Gini index estimates were high, particularly when the lower spatial scale of health units was evaluated. The Gini index appears to be inversely associated to annual parasite-incidence, as well as the proportions of vivax malaria, male sex, and adults.

Interpretation

This study suggests that areas with varying levels of transmission-intensities exhibited distinct characteristics. Malaria was distributed in a markedly disproportionate manner throughout the region, emphasising the need for spatially targeted interventions. Periodic quantification and characterisation of risk heterogeneity at various spatial levels using routine malaria surveillance data may aid in tracking progress towards elimination and guiding evidence-informed prioritisation of resource allocation.

Funding

Strengthening Preparedness in the Asia-Pacific Region through Knowledge (SPARK) project.

Research in context

Evidence before this study

We searched PubMed up to and including November 19, 2021, for relevant articles on the spatial distribution of malaria in the Papua region of Indonesia, using the terms (“malaria”) AND (“distribution” OR “variation” OR “heterogeneity” OR “cluster” OR “aggregation”) AND (“Papua”) AND (“Indonesia”). Despite the region’s mostly stable transmission areas, there has been considerable variation in transmission intensity across the region. According to community surveys conducted up to 2010, estimates of parasite prevalence of Plasmodium falciparum and Plasmodium vivax were highly variable, ranging from 0% to at least 40% and from 0% to at least 7%, respectively, across the region. Similarly, when the Papuan subset of the 2007 National Basic Health Research data was used, the degree of spatial heterogeneity in malaria risk among Papuan districts remained apparent even after sociodemographic were adjusted. Current evidence that is more representative of the current situation, including an easily interpretable and comparable measure of spatial heterogeneity across space and time, is limited.

Added value of this study

Our analysis of large-scale and routinely collected malaria surveillance data from January 2019 to December 2020 revealed significant spatial heterogeneity across the Papua region, as measured by the Gini index. Complementing conventional approaches using geospatial maps and risk tables, the Gini index can be used to provide a single, and sensitive numerical indicator summarising the degree of transmission heterogeneity at a specified spatial level of interest. Along with the previously recognised high spatial heterogeneity among districts, this study revealed a greater degree of intra-district heterogeneity at the health-unit level. That is, within the districts, there were also few health centres and hospitals with a disproportionately higher malaria burden. We observed distinct characteristics of individuals who contracted malaria in districts with varying levels of incidence. The higher transmission magnitude was associated with a lower Gini index, as well as with lower proportions of vivax malaria, male sex, and adults among the cases.

Implications of all the available evidence

This study provides contemporary empirical evidence for the spatial heterogeneity of malaria distribution across the Papua region of Indonesia, particularly at the lower spatial resolution of health units. Evaluating spatial heterogeneity at a lower spatial scale is likely essential to refine and update local malaria control strategic planning. The combination of comprehensive, routine malaria surveillance data and the Gini index may enable policymakers to assess the magnitude and characteristics of spatial heterogeneity with increased frequency, interpretability, and comparability, allowing for the rapid identification of transmission foci and the deployment of public health measures. Effective control of parasite reservoirs associated with intense transmission may further shrink the risk of infection in adjacent areas with a lower degree of malaria exposure.