Trachoma, caused by ocular infection with Chlamydia trachomatis, is the leading infectious cause of blindness globally. To advance elimination as a public health problem, Naoero implemented two rounds of antibiotic mass drug administration (MDA) with azithromycin, reaching estimated population coverage of 87% and 93% for the first and second rounds respectively. This study aimed to measure the impact of these two MDA rounds by estimating the post-MDA prevalence of clinical trachoma and ocular C. trachomatis infection in children aged 1–9 years, and to document household water, sanitation, and hygiene (WASH) conditions.
Investigators conducted a two-stage cluster sampled impact survey 12 months after the second MDA round. All residents aged ≥1 year within sampled clusters were examined for signs of trachoma. Conjunctival swabs for PCR testing for C. trachomatis were collected from children aged 1–9 years. Data were also gathered on household access to improved water sources for hygiene and access to improved latrines. Age-adjusted prevalence estimates and 95% confidence intervals were calculated for clinical and laboratory outcomes.
A total of 2,150 residents were examined in the survey, including 724 children aged 1–9 years who contributed conjunctival swabs for PCR testing. For adult and older adolescent screening relevant to trachomatous trichiasis (TT), 1,114 residents aged ≥15 years were examined.
The age-adjusted prevalence of trachomatous inflammation–follicular (TF) among children aged 1–9 years was 6.0% (95% CI 3.9–7.7). The age-adjusted prevalence of ocular C. trachomatis infection in the same age group, measured by PCR, was 2.7% (95% CI 0.3–5.1).
One case of TT previously unknown to the health system was identified in a resident aged ≥15 years among the 1,114 examined. The age- and gender-adjusted prevalence of TT was estimated at 0.04% (95% CI 0–0.12).
The authors compared the post-MDA prevalence of C. trachomatis infection to a pre-MDA estimate and reported that the PCR-based prevalence was substantially reduced from the pre-MDA level of 39.4%, indicating that the antibiotic MDA had a measurable impact on infection prevalence.
Household-level data documented high access to WASH services: 99.8% of households reported access to an improved water source for hygiene purposes, and 99% reported access to an improved latrine. These high coverage figures were reported alongside the clinical and laboratory results.
Following two rounds of azithromycin MDA with high estimated coverage, the prevalence of ocular C. trachomatis infection in children was markedly lower than pre-MDA levels, and the TF prevalence was measured at 6.0% in 1–9-year-olds. According to the authors, the measured TF prevalence after MDA was above the World Health Organization threshold used to indicate elimination as a public health problem, whereas the TT prevalence was below that threshold.
The study authors emphasise the potential added value of incorporating PCR-based infection data alongside clinical signs when making programmatic decisions, particularly in post-MDA settings or areas with low TF prevalence. However, they note that standardised thresholds for interpreting community-level C. trachomatis prevalence determined by PCR have not yet been established and are urgently needed to guide future interventions.
Details about specific timing of each MDA round, the precise diagnostic platform and laboratory procedures for PCR, breakdowns of age- or sex-specific prevalence beyond the reported aggregates, and potential non-participation rates were not reported in the abstract. The authors call for standardised interpretive thresholds for PCR-based C. trachomatis prevalence to be defined so such data can be formally integrated into elimination decision-making.
The manuscript discloses that some authors are employed by or receive salary support from organisations linked to the International Trachoma Initiative, which receives funding from Pfizer Inc., manufacturer of azithromycin. The authors state these relationships do not alter adherence to journal policies on sharing data and materials.