General contextual effects on neglected tropical disease risk in rural Kenya.

William A De Glanville,Samuel Kariuki,Barend M De C Bronsvoort,Elizabeth A J Cook,Eric M Fèvre,Claire N Wamae,Lian F Thomas,Nicola Wardrop

doi:10.1371/journal.pntd.0007016

Abstract

The neglected tropical diseases (NTDs) are characterized by their tendency to cluster within groups of people, typically the poorest and most marginalized. Despite this, measures of clustering, such as within-group correlation or between-group heterogeneity, are rarely reported from community-based studies of NTD risk. We describe a general contextual analysis that uses multi-level models to partition and quantify variation in individual NTD risk at multiple grouping levels in rural Kenya. The importance of general contextual effects (GCE) in structuring variation in individual infection with Schistosoma mansoni, the soil-transmitted helminths, Taenia species, and Entamoeba histolytica/dispar was examined at the household-, sublocation- and constituency-levels using variance partition/intra-class correlation co-efficients and median odds ratios. These were compared with GCE for HIV, Plasmodium falciparum and Mycobacterium tuberculosis. The role of place of residence in shaping infection risk was further assessed using the spatial scan statistic. Individuals from the same household showed correlation in infection for all pathogens, and this was consistently highest for the gastrointestinal helminths. The lowest levels of household clustering were observed for E. histolytica/dispar, P. falciparum and M. tuberculosis. Substantial heterogeneity in individual infection risk was observed between sublocations for S. mansoni and Taenia solium cysticercosis and between constituencies for infection with S. mansoni, Trichuris trichiura and Ascaris lumbricoides. Large overlapping spatial clusters were detected for S. mansoni, T. trichiura, A. lumbricoides, and Taenia spp., which overlapped a large cluster of elevated HIV risk. Important place-based heterogeneities in infection risk exist in this community, and these GCEs are greater for the NTDs and HIV than for TB and malaria. Our findings suggest that broad-scale contextual drivers shape infectious disease risk in this population, but these effects operate at different grouping-levels for different pathogens. A general contextual analysis can provide a foundation for understanding the complex ecology of NTDs and contribute to the targeting of interventions.

Highlights

People living in rural areas in sub-Saharan Africa are often at high risk of infection with a range of pathogens [1,2,3]
Co-efficients from the adjusted models (M2) for each pathogen are shown in Table 2 (STH and S. mansoni), Table 3 (E. histolytica/dispar, Taenia spp. and T. solium) and Table 4 (HIV, P. falciparum, M. tuberculosis)
There was no evidence of a relationship between sex and A. lumbricoides (Table 2), M. tuberculosis, or P. falciparum (Table 4) infection

Summary

Introduction

People living in rural areas in sub-Saharan Africa are often at high risk of infection with a range of pathogens [1,2,3]. All else being equal, two people living in the same group will tend to be more similar in their health status than two people living in different groups [12]. Such clustering effects are often large for infectious diseases, and so at the household-level for pathogens that are spread through poor sanitation, contaminated water, endophagic vectors, and unhygienic practices [13,14,15,16,17,18]

Objectives

Methods

Results

Discussion

Conclusion