Defining Seropositivity Thresholds for Use in Trachoma Elimination Studies

Area of Science:

• Ophthalmology
• Infectious Diseases
• Public Health

Background:

• Trachoma elimination efforts face challenges with current clinical sign assessments.
• Clinical signs correlate poorly with Chlamydia trachomatis (Ct) infection post-treatment and in low-endemic settings.
• Age-specific seroprevalence of anti-Ct Pgp3 antibodies is a potential indicator for intervention needs.

Purpose of the Study:

• To develop and standardize reproducible analytical approaches for anti-Ct Pgp3 antibody seroprevalence studies.
• To compare different statistical methods for defining serological status in trachoma surveillance.
• To establish reliable indicators for guiding trachoma intervention strategies.

Main Methods:

• Dried blood spots were collected from children and adults in Laos, Uganda, and The Gambia.
• Anti-Pgp3 antibodies were quantified using Enzyme-Linked Immunosorbent Assay (ELISA).
• Visual and statistical analytical methods, including expectation-maximisation and finite mixture models, were compared for seroprevalence estimation.

Main Results:

• Different analytical methods yielded varying seroprevalence estimates across study sites.
• Internally calibrated threshold methods showed consistency and reproducibility.
• Receiver operating characteristic (ROC) curve analysis with external calibration underestimated seroprevalence compared to internal methods.

Conclusions:

• Internally calibrated threshold specification approaches are reproducible and advantageous over external calibrators.
• Finite mixture models or expectation-maximisation algorithms are recommended for setting ELISA thresholds in future trachoma serological analyses.
• Standardized, internally calibrated methods will facilitate harmonized trachoma studies and eliminate the need for global calibration standards.