Exploring the spatial heterogeneity of trachomatous trichiasis

Prolonged conjunctival infection with Chlamydia trachomatis leads to an inflammatory response, trachomatous inflammation follicular (TF). Over time, repeat infection can progress to scarring of the conjunctiva causing the eyelid to turn inward, resulting in lashes rubbing against the cornea. This painful stage of the disease is called trachomatous trichiasis (TT). TT can damage the cornea, leading to vision impairment or blindness. Trachoma is targeted for elimination as a public health problem by the year 2020, which for TT is defined as less than 1 TT-positive person, who is not already known to the health system, per 1,000 population. For trachoma to meet the elimination targets, massive resources are required for both mapping and intervention. A particularly large knowledge gap exists around identifying areas where TT is likely to be found. To better align resources and plan for elimination, the trachoma community needs to understand how much TT currently exists and requires management, how to accurately measure TT prevalence, and where TT cases are mostly likely to be located. Understanding these elements will help position trachoma control programs to meet the TT elimination targets. In my thesis I first calculate an updated global estimate of TT cases and describe the methods involved. Second, I provide a survey design for measuring TT with adequate precision for control activities, along with validation exercise results and a brief time-cost analysis. I then examine the spatial structure of TF and TT and identify areas of spatial autocorrelation. Finally, I identify environmental factors associated with higher than expected TT prevalence to identify TT hot spots. The outcomes of these activities provide an updated global estimate of existing TT cases, a validated tool for measuring TT prevalence at the implementation unit (district) level, and insight on where to begin case finding activities in the context of the “end game”. These outputs are critical to the continued effort of trachoma elimination as a public health problem, specifically providing targeted direction for TT resources.