Field Evaluation of the Cepheid GeneXpert Chlamydia trachomatis Assay for Detection of Infection in a Trachoma Endemic Community in Tanzania

Abstract

PurposeTo determine the sensitivity, specificity, and field utility of the Cepheid GeneXpert Chlamydia trachomatis (CT) Assay (GeneXpert) for ocular chlamydia infection compared to Roche Amplicor CT assay (Amplicor).MethodsIn a trachoma-endemic community in Kongwa Tanzania, 144 children ages 0 to 9 were surveyed to assess clinical trachoma and had two ocular swabs taken. One swab was processed at Johns Hopkins University, Baltimore MD, using Amplicor, (Roche Molecular Diagnostics) and the other swab was processed at a field station in Kongwa using the GeneXpert Chlamydia trachomatis/Neisseria gonorrhoeae assay (Cepheid). The sensitivity and specificity of GeneXpert was compared to the Amplicor assay.ResultsOf the 144 swabs taken the prevalence of follicular trachoma by clinical exam 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 more positives in individuals with clinical trachoma than Amplicor, 55% versus 52%.ConclusionThe GeneXpert test for C. trachomatis performed with high sensitivity and specificity and demonstrated excellent promise as a field test for trachoma control.

Evaluation of pooled ocular and vaginal swabs by the Cepheid GeneXpert CT/NG assay for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae compared to the GenProbe Aptima Combo 2 Assay

“…NAAT assays currently used for detecting ocular and genital infections can be costly at $10 to $15/test, plus labor charges (Goodhew et al, 2012; See et al, 2011). Pooling specimens before testing by NAATs for the detection of CT and NG can potentially reduce the cost associated with estimating the prevalence of ocular CT infections in the field of trachoma-endemic countries (Dize et al, 2013; Jenson et al, 2013) as well as for diagnosing CT and NG genital infections in clinical settings. Previously, high sensitivity and specificity as well as large cost savings have been demonstrated when testing pools of 4 or 5 genital or ocular samples by NAATs compared to individual testing (Dize et al, 2013; Kacena et al, 1998; Shipitsyna et al, 2007).…”

“…The limited amount of “hands-on” time and the ease of use of the GeneXpert make this assay ideal in clinics with “express visits” as well as for use in developing countries that lack sophisticated laboratory equipment and infrastructure for specialized NAAT testing where trachoma is endemic. Although GeneXpert is a NAAT PCR assay, the test platform is relatively simple and was previously evaluated for ocular swab testing in the field at the Kongwa Trachoma Project in Tanzania and resulted in a positive experience suggesting that pooling on GeneXpert could also be performed in the field (Jenson et al, 2013). …”

Toward the Elimination of Disease: the 2019 Weisenfeld Award Lecture

“…Currently, there is machinery for such testing that is robust, well validated, relatively inexpensive, and easy to use in field settings. 26 A test for infection is more precise than the assessment of clinical disease. However, these tests are expensive, and because they are so sensitive, they may detect a trivial load of infection, one not capable of transmission.…”

Sample-to-result molecular infectious disease assays: clinical implications, limitations and potential

“…One study collected ocular samples in Tanzania and tested them in a U.S. laboratory on the GeneXpert CT/NG assay, achieving 100% sensitivity and specificity compared with another molecular assay (Roche Amplicor CT/NG). In a subsequent study, [100] the researchers collected two swabs from the same eye on 144 children under 9 years old. One swab was tested on the Xpert CT/NG assay in the field in Tanzania, and the other swab was sent to the U. S. for testing on the Roche Amplicor CT/NG test.…”