Spatial clustering of high load ocular Chlamydia trachomatis infection in trachoma: a cross-sectional population-based study.

Anna Last,Chrissy H Roberts,Emma Harding-Esch,Meno Nabicassa,Eunice Teixeira Da Silva Cassama,Martin Holland,Neal Alexander,David Mabey,Sarah Burr,Robin Bailey

doi:10.1093/femspd/ftx050

Abstract

Chlamydia trachomatis (Ct) is the most common cause of bacterial sexually transmitted infection and infectious cause of blindness (trachoma) worldwide. Understanding the spatial distribution of Ct infection may enable us to identify populations at risk and improve our understanding of Ct transmission. In this study, we sought to investigate the spatial distribution of Ct infection and the clinical features associated with high Ct load in trachoma-endemic communities on the Bijagós Archipelago (Guinea Bissau). We collected 1507 conjunctival samples and corresponding detailed clinical data during a cross-sectional population-based geospatially representative trachoma survey. We used droplet digital PCR to estimate Ct load on conjunctival swabs. Geostatistical tools were used to investigate clustering of ocular Ct infections. Spatial clusters (independent of age and gender) of individuals with high Ct loads were identified using local indicators of spatial association. We did not detect clustering of individuals with low load infections. These data suggest that infections with high bacterial load may be important in Ct transmission. These geospatial tools may be useful in the study of ocular Ct transmission dynamics and as part of trachoma surveillance post-treatment, to identify clusters of infection and thresholds of Ct load that may be important foci of re-emergent infection in communities.

Highlights

Chlamydia trachomatis is the leading infectious cause of blindness and the most common sexually transmitted bacterium
The geometric mean of estimated omcB copies/swab present in clinically normal conjunctivae (F0/P0/C0) was 294 copies/swab (95% C.I. 165-524)
Further longitudinal data in the context of trachoma endemicity and mass drug treatment are required to fully address these questions and investigate the dynamics of C. trachomatis load in transmission. This is the first study to use individual-level quantifiable C. trachomatis infections from a geospatially representative population-based sample to investigate spatial clustering of C. trachomatis infection. These data show that increasing C. trachomatis load is related to increasing disease severity in active trachoma, with respect to inflammation

Summary

Introduction

Chlamydia trachomatis is the leading infectious cause of blindness and the most common sexually transmitted bacterium. Understanding the spatial distribution of disease and infection in trachoma-endemic regions is increasingly recognized in national trachoma control programme planning, enabling the identification of at risk populations and prioritization of target areas for control and implementation and optimal scaling of SAFE [4,5,6,7,8]. It may be important in understanding transmission, transmission thresholds and the dynamics of spread and recovery from infection following intervention

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