Optimization of a rapid test for antibodies to the Chlamydia trachomatis antigen Pgp3

Area of Science:

• Ophthalmology
• Infectious Diseases
• Public Health

Background:

• Serological surveillance is crucial for monitoring trachoma transmission, especially after elimination targets are met.
• Feasible testing platforms are needed for resource-limited settings.
• Dried blood spots (DBS) offer a convenient sample type for serologic testing.

Purpose of the Study:

• To evaluate the feasibility and accuracy of different serologic testing platforms for trachoma surveillance.
• To assess antibody prevalence against the Pgp3 antigen in a Tanzanian population.
• To compare the performance of lateral flow assays (LFAs) with a bead-based multiplex assay (MBA) using DBS.

Main Methods:

• Blood samples (whole blood, plasma, DBS) were collected from 506 children aged 1-12 years in Tanzania.
• Antibodies against Pgp3 antigen were tested using a cassette-enclosed LFA (LFA-cassette), a dipstick LFA (LFA-dipstick), and a bead-based multiplex assay (MBA).
• Testing was conducted in both laboratory and field settings, with interrater agreement assessed.

Main Results:

• Antibody positivity rates against Pgp3 were similar across all tested formats (MBA, LFA-cassette, LFA-dipstick), ranging from 42.5% to 48.4%.
• There were no significant differences in positivity between the multiplex assay and either lateral flow assay format.
• Excellent interrater agreement (Cohen's kappa >0.81) was observed between expert and field raters across all settings.

Conclusions:

• Lateral flow assays, including a simple dipstick format, are reliable for serological surveillance of trachoma using DBS.
• These platforms are suitable for monitoring trachoma transmission in basic laboratory or field conditions.
• The findings support the use of accessible serologic tools for ongoing trachoma control efforts.