Cost-effectiveness of adding measurement of Chlamydia trachomatis infection and serology to trachoma prevalence surveys in Tanzania and Mozambique

Background: Accurate methods to measure trachoma prevalence are critical to monitor progress and guide mass drug administration as countries near elimination. Currently, countries conduct trachoma prevalence surveys via clinical examination using the simplified trachoma grading system. Grading can have reduced accuracy in low prevalence settings, potentially resulting in errors. Adding ocular swabbing and Chlamydia trachomatis (Ct) infection testing and dried blood spot (DBS) collection and testing can be more sensitive and specific methods for trachoma identification, with potential cost-saving and information benefits. While previous studies have examined the costs of trachoma prevalence surveys, we present the first costing and cost-effectiveness analysis of enhanced trachoma prevalence surveys with ocular swabs and DBS in addition to grading. Methodology/Principal findings: We calculated the incremental financial cost of enhanced trachoma prevalence surveys with swabs, DBS, and grading using expenditure records from four districts in Tanzania and four districts in Mozambique in 2022. In Tanzania, the cost per cluster of an enhanced survey was $2,337.39 compared to $459.75 for a standard survey. In Mozambique, the cost per cluster of an enhanced survey was $2,147.12, compared to $1,381.46 for a standard survey. We calculated the incremental cost-effectiveness ratio for each method, defined as the ratio of incremental cost to additional instances of trachoma indicators identified, and explored variation in cost-effectiveness via sensitivity analyses. Adding swabs, DBS, or both was cost-increasing and more effective at identification of trachoma indicators than grading alone. In Tanzania, swabs were the most cost-effective method, while DBS was more cost-effective in Mozambique. Swabs and DBS were less cost-effective when combined than individually. The main factor determining cost-effectiveness was sensitivity. Conclusions/Significance: Adding swabs or DBS to trachoma prevalence surveys can be viable, cost-effective methods for identifying trachoma indicators. The additional costs are commensurate with additional information that would support elimination efforts. Author summary: Countries have made progress towards eliminating trachoma, a bacterial blinding disease. To assess trachoma prevalence, countries conduct surveys involving examination for clinical signs of trachoma, which in turn inform the decision to implement mass drug administration of antibiotics. However, clinical examination can result in errors, particularly as the disease becomes rare. Countries have explored alternative methods of identifying trachoma, which include testing swabs of the inner eyelid or dried blood spots (DBS). These methods can be more accurate than clinical examination, but also more costly. We examined the costs of surveys with swabs and DBS in Tanzania and Mozambique compared to surveys with clinical examination alone. We found that adding swabs and DBS to a survey increased costs by 408% in Tanzania and 55% in Mozambique. We also assessed cost-effectiveness, or the extent to which additional costs corresponded to greater trachoma indicator identification, and found that swabs were most cost-effective in Tanzania, while DBS were most cost-effective in Mozambique. Using both swabs and DBS together in a survey added the most costs, with similar gain in trachoma identification compared to using one or the other. Our results will help countries plan for future surveys.