Explaining the continuing high prevalence of trachomatous trichiasis unknown to the health system in evaluation units: a mixed methods explanatory study in four trachoma-endemic countries.

Background: We explored reasons for continuing higher-than-anticipated prevalence of trachomatous trichiasis (TT) unknown to the health system in population-based prevalence surveys in evaluation units where full geographical coverage of TT case finding was reported.

Methods: A mixed-methods study in Ethiopia, Kenya, Nigeria and Tanzania was conducted. We compared data from clinical examination, campaign documentation and interviews with original trachoma impact survey (TIS) results.

Results: Of 169 TT cases identified by TIS teams, 130 (77%) were examined in this study. Of those, 90 (69%) were a match (both TIS and study teams agreed on TT classification) and 40 (31%) were a mismatch. Of the 40 mismatches, 22 (55%) were identified as unknown to the health system by the study team but as known to the health system by the TIS team; 12 (30%) were identified as not having TT by the study team but as having TT by the TIS team; and six (15%) were identified as unknown to the health system in the TIS team but as known to the health system by the study team based on documentation reviewed.

Conclusions: Incorrectly reported geographical coverage of case-finding activities, and discrepancies in TT status between TIS results and more detailed assessments, are the key reasons identified for continuing high TT prevalence.