PROJECT SUMMARY/ABSTRACT Annual mass azithromycin distribution dramatically reduces the prevalence strains of Chlamydia trachomatis that lead to blindness. Current World Health Organization guidelines indicate that annual mass azithromycin distribution should be continued until district-level prevalence of the clinical sign of trachoma, trachomatous inflammation-follicular (TF), drops below 5%. However, TF doesn’t correlate well with true prevalence and there is no gold standard to detect this. Here, we propose that a Hidden Markov Model 1) will identify the true prevalence in hypo-endemic areas that can be used as a signal that the mass azithromycin protocol was successful and an indicator to stop antibiotics and 2) identify hyperendemic areas that the protocol has not been successful to change the treatment regimen. We anticipate that results will provide evidence to support altering the modification of current interventions for trachoma.