DjinniChip: evaluation of a novel molecular rapid diagnostic device for the detection of Chlamydia trachomatis in trachoma-endemic areas

Abstract

Background: The clinical signs of active trachoma are often present in the absence of ocular Chlamydia trachomatis infection, particularly following mass drug administration. Treatment decisions following impact surveys and in post-control surveillance for communities are currently based on the prevalence of clinical signs, which may result in further unnecessary distribution of mass antibiotic treatment and the increased spread of macrolide resistance alleles in 'off-target' bacterial species. We therefore developed a simple, fast, low cost diagnostic assay (DjinniChip) for diagnosis of ocular C. trachomatis for use by trachoma control programmes.

Methods: The study was conducted in the UK, Germany and Tanzania. For clinical testing in Tanzania, specimens from a sample of 350 children between the ages of 7 to 15 years, which were part of a longitudinal cohort that began in February 2012 were selected. Two ocular swabs were taken from the right eye. The second swab was collected dry, kept cool in the field and archived at - 80 °C before sample lysis for DjinniChip detection and parallel nucleic acid purification and detection/quantification by qPCR assay.

Results: DjinniChip was able to reliably detect > 10 copies of C. trachomatis per test and correctly identified 7/10 Quality Control for Molecular Diagnostics C. trachomatis panel samples, failing to detect 3 positive samples with genome equivalent amounts ≤ 10 copies. DjinniChip performed well across a range of typical trachoma field conditions and when used by lay personnel using a series of mock samples. In the laboratory in Tanzania, using clinical samples the sensitivity and specificity of DjinniChip for C. trachomatis was 66% (95% CI 51-78) and 94.8 (95% CI 91-97%) with an overall accuracy of 90.1 (95% CI 86.4-93).

Conclusions: DjinniChip performance is extremely promising, particularly its ability to detect low concentrations of C. trachomatis and its usability in field conditions. The DjinniChip requires further development to reduce inhibition and advance toward a closed system. DjinniChip results did not vary between local laboratory results and typical trachoma field settings, illustrating its potential for use in low-resource areas to prevent unnecessary rounds of MDA and to monitor for C. trachomatis recrudescence.

Keywords: Chlamydia trachomatis; LAMP; Lateral flow assay; Rapid test; Trachoma.

Fig. 1

Schematic principle of the DjinniChip. a Principle of the detection of LAMP product on LFS. b Components and processes. The DjinniChip contains lyophilized reagents (1) and a lateral flow test strip (2). A liquid sample (3) is loaded onto the chip through its inlet. The liquid sample reconstitutes the reagents (4). Chlamydia trachomatis DNA is amplified at 65 °C. The reaction mix is pumped gently with a syringe to the lateral flow test (5). The appearance of the Control band (C) indicates the correct function of the lateral flow test. The appearance of the Test band (T) indicates the presence of C. trachomatis in the sample. c Detection on DjinniChips

Fig. 2

Concentration of C. trachomatis positive clinical samples by reference qPCR in target copies per microlitre of extracted DNA, showing those diagnosed as positive (blue circles, pos) and negative (red circles, neg) by the DjinniChip