Changes in trachoma indicators in Kiribati with two rounds of azithromycin mass drug administration, measured in serial population-based surveys

Abstract

Baseline mapping in the two major population centers of Kiribati showed that trachoma was a public health problem in need of programmatic interventions. After conducting two annual rounds of antibiotic mass drug administration (MDA), Kiribati undertook trachoma impact surveys in 2019, using standardized two-stage cluster surveys in the evaluation units of Kiritimati Island and Tarawa. In Kiritimati, 516 households were visited and in Tarawa, 772 households were visited. Nearly all households had a drinking water source and access to an improved latrine. The prevalence of trachomatous trichiasis remained above the elimination threshold (0.2% in ≥15-year-olds) and was virtually unchanged from baseline. The prevalence of trachomatous inflammation—follicular (TF) in 1–9-year-olds decreased by approximately 40% from baseline in both evaluation units but remained above the 5% TF prevalence threshold for stopping MDA. TF prevalence at impact survey was 11.5% in Kiritimati and 17.9% in Tarawa. Infection prevalence in 1–9-year-olds by PCR was 0.96% in Kiritimati and 3.3% in Tarawa. Using a multiplex bead assay to measure antibodies to the C. trachomatis antigen Pgp3, seroprevalence in 1–9-year-olds was 30.2% in Kiritimati and 31.4% in Tarawa. The seroconversion rate, in seroconversion events/100 children/year, was 9.0 in Kiritimati and 9.2 in Tarawa. Seroprevalence and seroconversion rates were both assessed by four different assays, with strong agreement between tests. These results show that, despite decreases in indicators associated with infection at impact survey, trachoma remains a public health problem in Kiribati, and provide additional information about changes in serological indicators after MDA.

Author summary

This study compares different indicators for the eye disease trachoma before and after two annual rounds of mass azithromycin treatment of affected communities of Kiribati. We saw decreases in the proportion of children with the sign TF (trachomatous inflammation—follicular) that is used by trachoma programs to make decisions about starting and stopping mass treatment, but these decreases were not sufficient to make the decision to stop. We also saw decreases in infection and antibody levels after treatment. The study provides important public health information to Kiribati trachoma programs, but also adds to the growing body of evidence to guide the use of alternative indicators–infection and antibody–to support these programs. Measuring antibody levels in communities over time helps us understand how antibody levels change as community infection prevalence decreases. Understanding antibody dynamics over time can help us better estimate antibody-based thresholds for surveillance after elimination of trachoma as a public health problem.