Distance to Anopheles sundaicus larval habitats dominant among risk factors for parasitemia in meso-endemic Southwest Sumba, Indonesia

Abstract

Background: The decline in intensity of malaria transmission in many areas now emphasizes greater importance of understanding the epidemiology of low to moderate transmission settings. Marked heterogeneity in infection risk within these populations creates opportunities to understand transmission and guide resource allocation to greater impact.

Methods: In this study, we examined spatial patterns of malaria transmission in a hypo- to meso-endemic area of eastern Indonesia using malaria prevalence data collected from a cross-sectional socio-demographic and parasitological survey conducted from August to November 2010. An entomological survey performed in parallel, identified, mapped, and monitored local anopheline larval habitats.

Results: A single spatial cluster of higher malaria prevalence was detected during the study period (relative risk  =  2·13; log likelihood ratio  =  20·7; P < 0·001). In hierarchical multivariate regression models, risk of parasitemia was inversely correlated with distance to five Anopheles sundaicus known larval habitats [odds ratio (OR)  =  0·21; 95% confidence interval (CI)  =  0·14–0·32; P < 0·001], which were located in a geographically restricted band adjacent to the coastline. Increasing distance from these sites predicted increased hemoglobin level across age strata after adjusting for confounders (OR  =  1·6; 95% CI  =  1·30–1·98; P < 0·001).

Conclusion: Significant clustering of malaria parasitemia in close proximity to very specific and relatively few An. sundaicus larval habitats has direct implications for local control strategy, policy, and practice. These findings suggest that larval source management could achieve profound if not complete impact in this region.

Keywords:

• Anopheles sundaicus
• Larval habitats
• Malaria risk factors
• Spatial scan statistic

Acknowledgements

The authors thank Prof. Sangkot Marzuki of the Eijkman Institute for support, the public officials of the Southwest Sumba District offices for encouragement and support, the Village Chief and local volunteers of Wainyapu for their generous assistance and the residents of Wainyapu for their interest and enthusiasm for participating in the study. We also extend our gratitude to Stacey Maples M.Sc. of the Yale University Library Department of Map Collections and Thomas Mayo M.Sc. for geographical information systems guidance and critical review of the manuscript. C. P. Nixon also gratefully thanks the University of California San Francisco, Department of Pathology for encouragement and support to participate in this project.