Evaluation of the new COBAS TaqMan CT test v2.0 and impact on the proportion of new variant Chlamydia trachomatis by the introduction of diagnostics detecting new variant C trachomatis in Orebro county, Sweden.

BACKGROUND

The new variant of Chlamydia trachomatis (nvCT), discovered in Sweden in 2006, contains a 377-bp cryptic plasmid deletion, which includes the targets for the COBAS Amplicor/TaqMan C trachomatis/Neisseria gonorrhoea and Abbott m2000rt C trachomatis/N gonorrhoea tests.

OBJECTIVES

To evaluate the new real-time COBAS TaqMan CT test v2.0 (CTM CT v2.0) for C trachomatis diagnostics and to investigate whether the proportion of nvCT was affected by the introduction of genetic diagnostics detecting nvCT (LightMix 480HT) in Orebro county, Sweden.

METHODS

CTM CT v2.0 compared with LightMix 480 HT PCR for the diagnosis of C trachomatis was evaluated. Discrepant samples were analysed using BD ProbeTec ET and Abbott m2000rt RealTime CT II. All previously LightMix and cell culture-positive samples were analysed using an nvCT-specific PCR.

RESULTS

The sensitivity, specificity, negative predictive value and positive predictive value of CTM CT v2.0 for examined samples (n = 1058) was 100%, 99.8%, 100% and 98.2%, respectively. Of 11,577 consecutive PCR samples, 9.4% (n = 1084) were positive and 34.3% (n = 372) of these were nvCT. Of 2306 consecutive culture samples, 5.0% (n = 116) were C trachomatis positive and 38.8% (n = 45) of these were nvCT.

CONCLUSIONS

CTM CT v2.0 is a sensitive and specific method for C trachomatis detection. Studies including larger numbers of symptomatic and asymptomatic patients as well as genital and extragenital samples, and in comparison with other internationally validated and, ideally, US Food and Drug Administration-approved C trachomatis nucleic acid amplification tests are imperative. The proportion of nvCT remains high in Orebro county, Sweden, despite the introduction of genetic diagnostics to detect the mutant.