Comparison of Methods for Assessing Chlamydia trachomatis Transmission Intensity: A Systematic Review

Field-graded trachomatous inflammation-follicular (TF) has limitations as the sole indicator of Chlamydia trachomatis (Ct) transmission for trachoma programmatic decision-making. To assess the relationship between field-graded TF and other methodologies for evaluating Ct transmission intensity, a systematic review was conducted. A total of 35,764 studies were screened, yielding 235 included studies from 49 countries spanning the years of data collection from 1991 to 2021 and the years of publication from 1991 to 2022. The relationship between TF and other indicators was stronger before mass drug administration (MDA) versus after MDA initiation: TF versus infection (R2 = 0.43, P = 0.004 versus R2 = 0.05, P = 0.140, respectively), TF versus seroprevalence (R2 = 0.55, P <0.001 versus R2 = 0.09, P = 0.084, respectively), and TF versus seroconversion rate (SCR; R2 = 0.52, P = 0.012 versus R2 = 0.26, P = 0.061, respectively). Post-MDA initiation, infection and SCR were highly correlated (R2 = 0.71, P = 0.001). These results are strongly suggestive of the poor performance of TF prevalence for guiding programmatic decision-making post-MDA initiation. Infection and/or serology should be considered in these settings.