What is the appropriate age range of individuals to be included in a survey to estimate the prevalence of trachomatous trichiasis?

Introduction: A survey to determine the prevalence of trachomatous trichiasis (TT) requires a large sample size and the recommended participant age is ≥15 years. This study sought to establish the appropriate age range of individuals to be included in TT surveys. Methods: Data from six previous surveys of adults ≥15 years old were reanalysed. Results: Reanalysis indicated that 69.6-93.3% (average 87.0%) of untreated TT occurred in those aged 40+ years and 52.2-86.7% (average 73.1%) in those aged 50+ years (age ≥50 years is used in rapid assessment of avoidable blindness). Age ≥40 years was adopted in a TT survey conducted in Turkana district because it allowed a smaller sample size than age ≥15 years. Conclusions: The estimated backlog of untreated TT in people aged ≥40 years old in Turkana was 5932 and the overall TT backlog was likely to be 6358-8523. These findings cannot be generalised because all surveys were carried out in the same country.