Impact of two rounds of azithromycin mass drug administration on active trachoma and ocular Chlamydia trachomatis infection in Naoero

Background Trachoma, caused by ocular infection with the bacterium Chlamydia trachomatis , is the primary infectious cause of blindness globally. To contribute to the elimination of trachoma as a public health problem, Naoero undertook two rounds of antibiotic mass drug administration (MDA) using azithromycin, with population-level coverage estimated at 87% and 93%. This study aimed to estimate the post-MDA prevalence of trachoma, and infection with C. trachomatis , in children aged 1–9 years. Methods A two-stage cluster sampled survey was conducted 12 months after the second MDA round. All residents aged ≥1 year were examined for signs of trachoma, and conjunctival swabs were collected from children aged 1–9 years for PCR testing. Data on domestic access to water, sanitation, and hygiene services were also collected. Results Overall, 2,150 residents were examined, with 724 aged 1–9 years. The age-adjusted prevalence of trachomatous inflammation—follicular (TF) in children aged 1–9 years was 6.0% (95%CI 3.9–7.7). The age-adjusted prevalence of C. trachomatis in the same age group was 2.7% (95%CI 0.3–5.1). There was evidence of trachomatous trichiasis (TT) previously unknown to the health system in one resident aged ≥15 years out of 1114 examined (age- and gender-adjusted prevalence 0.04%, 95%CI 0–0.12). Access to improved water sources for hygiene purposes was reported in 99.8% of households surveyed, and 99% of households reported access to an improved latrine. Conclusions In Naoero, the impact survey prevalence of TF was above, and of TT was below, the thresholds defined by WHO as indicating “elimination as a public health problem”. The C. trachomatis prevalence estimate was lower than it was pre-MDA (39.4%), demonstrating the impact of antibiotic MDA. Despite the potential value of PCR data in addition to clinical indicators to help inform the need for trachoma elimination interventions, particularly in post-MDA or low TF prevalence areas, standardised thresholds for interpreting C. trachomatis prevalence have yet to be established. They are urgently needed so that they can be formally used to guide future interventions.