Molecular Assay for Trachoma Field Evaluated

There is a need for a simple, inexpensive rapid test for Chlamydia trachomatis (CT) that can be performed in the field in trachoma endemic areas.

The gold standard for a laboratory test of infection is existing nucleic acid amplification tests that involve instrumentation that is expensive and requires developed laboratories not widely available in many trachoma endemic countries.

Scientists at the Johns Hopkins University (Baltimore, MD, USA) collected two ocular swabs from 144 children in a trachoma-endemic community in Kongwa (Tanzania) who were also assessed for clinical trachoma. A Dacron swab (Fisher HealthCare; Houston, TX, USA) was rotated and swiped across the upper conjunctiva three times and placed dry in a vial.

One swab was processed at Johns Hopkins University, using Amplicor (Roche Molecular Diagnostics; Pleasanton, CA, USA) and the other swab was processed at a field station in Kongwa using the GeneXpert Chlamydia trachomatis/Neisseria gonorrhoeae (CT/NG) assay (Cepheid; Sunnyvale, CA, USA). The sensitivity and specificity of GeneXpert was compared to the Amplicor assay.

Of the 144 swabs taken, the prevalence of follicular trachoma by clinical examination was 43.7%, and by evidence of infection according to Amplicor was 28.5%. A total of 17 specimens (11.8%) could not be processed by GeneXpert in the field due to lack of sample volume, other specimen issues, or electricity failure. The sensitivity of GeneXpert when compared to Amplicor was 100% and the specificity was 95%. The GeneXpert test identified 55% positives in individuals with clinical trachoma, while the Amplicor identified 52%.

The authors noted that the GeneXpert CT/NG assay was a research use only assay at the time of their study, but has now been approved by the US Federal Drug Administration (FDA; Silver Spring, MD, USA). The low cost of the processing platform, the ease of processing with readily available materials, plus the results show high sensitivity and specificity, suggesting this approach may be ideal for a field test for trachoma control programs. The study was published on July 4, 2013, in the journal Public Library of Science Neglected Tropical Disease.

Related Links:
Johns Hopkins University
Fisher HealthCare
Roche Molecular Diagnostics