Estimates of infection prevalence were derived from cross-sectional, population based prevalence surveys conducted since 1987, when surveys switched to the WHO simplified grading system. Surveys were identified using a combination of approaches, including:
1. Searches of electronic bibliographic databases
2. Searches of grey literature for reports and unpublished data
3. Direct contact with programme managers and researchers
TRA and anecdotal information were used to identify areas where trachoma is suspected to be endemic or non-endemic, or where trachoma has been found.
Each source was reviewed and data abstracted into a standardized Microsoft Excel spreadsheet. Abstracted data included the source of the data, location and year of the survey, survey methodology, characteristics of the surveyed population, number individuals examined and graded positive for trachoma. Prevalence of TF in children aged 1-9 years of age and TT in adults over 14 were the key indicators used in the mapping, but PCR and other diagnostic methods were recorded in the database when available. In the maps, any variation in the population age range or gender from these key age groups is specified in a footnote.