Can We Use Antibodies to Chlamydia trachomatis as a Surveillance Tool for National Trachoma Control Programs? Results from a District Survey

Abstract

Background: Trachoma is targeted for elimination by 2020. World Health Organization advises districts to undertake surveillance when follicular trachoma (TF) <5% in children 1-9 years and mass antibiotic administration has ceased. There is a question if other tools could be used for surveillance as well. We report data from a test for antibodies to C. trachomatis antigen pgp3 as a possible tool.

Methodology: We randomly sampled 30 hamlets in Kilosa district, Tanzania, and randomly selected 50 children ages 1-9 per hamlet. The tarsal conjunctivae were graded for trachoma (TF), tested for C. trachomatis infection (Aptima Combo2 assay: Hologic, San Diego, CA), and a dried blood spot processed for antibodies to C. trachomatis pgp3 using a multiplex bead assay on a Luminex 100 platform.

Principal findings: The prevalence of trachoma (TF) was 0.4%, well below the <5% indicator for re-starting a program. Infection was also low, 1.1%. Of the 30 hamlets, 22 had neither infection nor TF. Antibody positivity overall was low, 7.5% and increased with age from 5.2% in 1-3 year olds, to 9.3% in 7-9 year olds (p = 0.015). In 16 of the 30 hamlets, no children ages 1-3 years had antibodies to pgp3.

Conclusions: The antibody status of the 1-3 year olds indicates low cumulative exposure to infection during the surveillance period. Four years post MDA, there is no evidence for re-emergence of follicular trachoma.

Fig 1. Frequency of antibody levels to the chlamydial antigen pgp3 in 1–9 year olds.

Plot shows MFI-BG for antibody responses to pgp3 against the frequency of responders in each grouping of responses from 0 to 10⁵. The x-axis is shown as log ₁₀ MFI-BG. The green bar shows the cut-offs for each bead set.

Fig 2. Log of antibody response in children ages 1–9 years with and without Follicular Trachoma (TF).

The two bars correspond to the two cut-offs with each bead coupling. The X axis in each group corresponds to the result of a single child.

Fig 3. Log of Antibody Response in children ages 1–9 years who have and do not have Infection with C. trachomatis.

The two bars correspond to the two cut-offs with each bead coupling. The X axis in each group corresponds to the result of a single child.

Fig 4. Among the 22 hamlets with neither trachoma nor infection, the number of hamlets with zero proportion positive to pgp3, the number with 1-<10% positive, 10-<20% positive, and 20%+ positive, according to the proportion positive in the age group 1–3 years and in the age group 1–9 years.