Impact of the Global Trachoma Mapping Project

2020 is the target year for the global elimination of trachoma as a public health problem – a neglected tropical disease caused by ocular chlamydia infection. The World Health Organization (WHO) recommends the SAFE strategy for elimination: Surgery for trichiatic eyelashes, Antibiotics to clear ocular chlamydia, and Facial cleanliness and Environmental improvement to reduce transmission. Decisions for implementing the SAFE strategy are currently based on the prevalence of trachomatous inflammation – follicular (TF) among 1–9 year-olds and trachomatous trichiasis (TT) among adults age 15 years and older in affected communities; accurate trachoma mapping using standardized survey methodology is crucial for directing resources to the places they will have the greatest impact. In the early 2010s, it became clear that global elimination efforts were being hampered by incomplete mapping, and thus the Global Trachoma Mapping Project (GTMP) was initiated to provide much-needed data.¹ Ophthalmic Epidemiology has played an important role in dissemination, and the current issue is the last special issue devoted to the GTMP.

The scale and impact of the GTMP cannot be overestimated. Using a standardized, valid, reliable and reproducible methodology, the GTMP surveyed over 1546 districts and examined over 2.6 million people across 29 countries in just 3 years, making it the largest infectious disease survey ever undertaken.² The results of the GTMP were immediately relevant for national Ministries of Health, international nongovernmental organizations, and donors in their programmatic activities.³ And while mapping of some low-security areas is still required (e.g., South Sudan, Central African Republic, Yemen), the results have been immensely helpful for clarifying the progress toward global elimination. For example, this issue contains evidence that elimination may already have occurred in some countries (e.g., Nepal and Vietnam), and may be occurring faster than expected in others (e.g., Nigeria). In contrast, the mapping of Ethiopia, which is now complete after the publication of this special issue, confirms that Ethiopia remains the greatest challenge to global elimination.

Results from the GTMP underscore the importance of program planning based on local mapping data. For example, in the Pacific Island region the prevalence of TF among 1–9 year-olds was often greater than 10%, but TT among older individuals was much lower – an unexpected pattern that requires further study but suggests that surgical programs are not a great need in this region.^4,5 GTMP surveys in Chad⁶ and Senegal⁷ found the opposite pattern, with many evaluation units (EUs) showing a prevalence of TF below the WHO threshold for elimination (<5% TF) and a prevalence of trachomatous trichiasis above the elimination threshold (<0.2% TT), suggesting that surgical programs are a more urgent need. Achieving national elimination requires reaching WHO thresholds for both TF and trachomatous trichiasis and it is likely to be the latter that will be a major challenge in the coming years.

Several accomplishments of the GTMP should be mentioned above and beyond the actual mapping. GTMP enabled Ministries of Health to take ownership of the survey process, and became a catalyst for implementation, with trachoma interventions underway in all participating countries.^3,8 The rigorous GTMP methodology and the implementation of the surveys through handheld mobile devices was a tremendous capacity builder, training a cadre of health workers in epidemiologic assessment with applicability far beyond trachoma. Moreover, GTMP formed the foundation for Tropical Data, the successor to the GTMP that supports country efforts to perform impact assessments for trachoma.

As of November 2018, eight countries have achieved validation of trachoma elimination as a public health problem – Cambodia, Ghana, Islamic Republic of Iran, Lao People’s Democratic Republic, Mexico, Morocco, Nepal and Oman.⁹ The momentum is increasing and for more countries, achieving elimination by 2020 is indeed possible. By providing data on where interventions were most necessary, the GTMP sped the trajectory of trachoma elimination. By working closely with Ministries of Health, the GTMP established research infrastructure and capacity. Its work, now largely disseminated with the publication of this special issue, should be commended.