Response of active trachoma during modified antibiotic mass drug administration in four districts of northern Tanzania, 2022-2023: Results from repeated cross-sectional sentinel site monitoring using serological and molecular testing

BackgroundSince the first azithromycin mass drug administration (MDA) in 1999, Tanzania has made remarkable progress towards trachoma elimination. Yet several districts have seen prevalence of trachomatous inflammation--follicular (TF) in children aged 1-9 years remain or rebound [≥]5%. From 2022, Tanzania modified MDA implementation in these districts to either more frequent than annual (MFTA) or two additional annual MDA. Conducted in four districts receiving MFTA MDA (Longido and Ngorongoro) or annual MDA (Monduli and Simanjiro), our sentinel site monitoring study aimed to: 1) estimate TF prevalence, anti-Pgp3 serology measures, and ocular Chlamydia trachomatis (Ct) infection prevalence among children aged 1- 9 years; 2) characterize ocular Ct infection prevalence over time; and, 3) identify factors associated with ocular Ct infection and increasing community Ct infection prevalence. MethodsTen sentinel sites, with the highest prevalence of active trachoma, were selected per district. At each site, during three monitoring rounds just before MDA in June 2022, January 2023, and October 2023, 50 children aged 1-9 years were examined for trachoma clinical signs and had conjunctival swab and dried blood spot samples taken. ResultsThough ocular Ct infection prevalence declined, there was no change in TF prevalence, Pgp3 seroprevalence, or Pgp3 seroconversion during follow-up. Younger age, female gender, and more time required to collect water were associated with higher infection prevalence, and greater distance to a health facility was associated with increasing community infection prevalence. DiscussionFindings support shift from annual to MFTA MDA in Monduli, continued MFTA MDA in Longido and Ngorongoro, and "Wait and Watch" in Simanjiro. Annual monitoring and environmental improvement will be valuable alongside further investigation of relationships between water and sanitation conditions and ocular Ct infection in this setting. Prevalence surveys with additional molecular and serological testing are recommended in the four districts at the end of the MDA cycle. What is already known on this topicO_LIPersistent and recrudescent active trachoma is recognized as a late-stage challenge that prevents several countries from attaining elimination of trachoma as a public health problem. C_LIO_LIEvidence is lacking on how to optimally modify and monitor implementation of the surgery, antibiotics, facial cleanliness, and environmental change (SAFE) strategy in settings with persistent and recrudescent active trachoma. C_LI What this study addsO_LIWe selected sentinel sites with greatest likelihood of trachoma transmission in districts with persistent and recrudescent active trachoma to monitor changes over time of clinical, serological, and molecular measures of trachoma during modified mass drug administration (MDA). C_LIO_LIWe found fewer ocular Chlamydia trachomatis infections following MDA, though TF and serological measures were slow to respond to intervention. C_LIO_LIWe observed an association between water availability and individual infection and distance to a health facility with increasing community infection prevalence. C_LI How this study might affect research, practice, or policyO_LIOur study shows that enhanced monitoring using molecular and serological measures is useful for tailoring implementation of control interventions, like MDA. C_LIO_LISentinel site monitoring could be undertaken to help disease control programs decide whether to undertake substantive trachoma prevalence surveys and used for sero-surveillance for trachoma, once elimination has been validated. C_LI