# Model of yearly transition to severe trachomatous scarring and trichiasis in a cohort of women in Kongwa Tanzania

## TL;DR

This study models how trachomatous scarring progresses to trichiasis in women in Tanzania, showing that scarring can persist and lead to trichiasis for decades even after trachoma inflammation is eliminated.

## Contribution

The study provides the first model of the progression from scarring to trichiasis, highlighting the long-term need for TT management programs.

## Key findings

- The incidence of initial scarring (S1) is 4.7% per year, increasing with higher community prevalence of trachoma inflammation.
- Transition from severe scarring (S4) to trichiasis occurs at 2.6% per year.
- Once scarring reaches S2, further progression is independent of community trachoma prevalence.

## Abstract

One criterion for validation of trachoma elimination is the management of Trachomatous Trichiasis (TT) after Trachoma inflammation—follicular (TF) is eliminated in children ages 1–9 years at district level. No data exist on how long countries must have dedicated TT programs, as the timeline for progression to TT from trachomatous scarring is unknown. We used eight years of longitudinal data in women in Kongwa Tanzania to model progression from no scarring (S0) through grades of scarring severity (S1–S4) to TT. Markov models were used, with age, community prevalence of TF (CPTF), and household characteristics as co-variates. Adjusted for covariates, the incidence of S1 was estimated at 4∙7% per year, and the risk increased by 26% if the CPTF was between 5–10% and by 48% if greater than 10%. The transition from S4 to TT was estimated at 2∙6% per year. Districts, even after elimination of TF, may have some communities with TF ≥ 5% and increased risk of incident scarring. Once scarring progresses to S2, further progression is not dependent on CPTF. These data suggest that, depending on the district level of scarring and degree of heterogeneity in CPTF at the time of elimination, incident TT will still be an issue for decades.