assay for detecting Chlamydia trachomatis and Neisseria gonorrhoeae
Abdessalam Cherkaoui,1,*Gesuele Renzi,1Michele Mombelli, 1Katia Jaton,2Sabine Yerly,3Nicolas Vuilleumier4,5and Jacques Schrenzel1,6
Abstract
The Roche Cobas 6800 CT/NG assay was compared to the Abbottm2000 Real Time CT/NG assay for detecting Chlamydia trachomatis and Neisseria gonorrhoeae in 714 specimens referred to the bacteriology laboratory at Geneva University Hospitals, between November 2017 and March 2018, and in nine external quality controls for molecular diagnostics (seven from QCMD Glasgow and two from UK NEQAS). ForC. trachomatis,the sensitivity ofC6800 compared tom2000 was 100 % (95 % confidence interval [CI], 97.5 to 100 %), the specificity was 99.1 % (95 % CI, 98.0 to 99.7 %). For N. gonorrhoeae,the sensitivity of theC6800 compared tom2000 was 100 % (95 % CI, 90.5 to 100 %), whereas the specificity was 99.7 % (95 % CI, 98.9 to 99.9 %). The C6800 CT/NG assay appears to perform with great accuracy the detection of C. trachomatis and N.
gonorrhoeae.
Neisseria gonorrhoeaeandChlamydia trachomatisare con-sidered responsible for the most frequent bacterial sexually transmitted infections (STI) [1]. As the clinical presenta-tions of signs and symptoms can be confused with those of other STIs, an accurate diagnosis is capital for appropriate treatment and effective subsequent control strategies for STIs [1]. For both asymptomatic and symptomatic individ-uals, the diagnosis of N. gonorrhoeae and C. trachomatis relies on nucleic acid amplification tests (NAATs) which are sensitive, specific, reproducible, and robust [2, 3]. Nowadays various automated systems for the detection ofC. trachoma-tis and N. gonorrhoeae nucleic acid targets in urogenital samples are commercially available. Cobas 6800 CT/NG assay is a quantitative test that uses real-time polymerase chain reaction for the direct detection ofC. trachomatisand N. gonorrhoeae in oropharyngeal and anorectal swab and different urogenital specimens (urine, vaginal and endocer-vical swab specimens). The recommendation of the Center for Disease Control and Prevention is to perform, at least once a year, a screening of N. gonorrhoeae and C.
trachomatisin HIV-infected and at-risk men who have sex with men (MSM) by using oropharyngeal and rectal swab specimens [4]. Previous studies have reported that in MSM more than 80 % of the patients could be missed when only urogenital sites were screened [4–7]. Moreover, the study conducted by David Hardy et al., showed good analytical performances for the Cobas 6800 CT/NG assay to detect both pathogens in oropharyngeal and anorectal swab speci-mens [8].
The objective of this study was to assess the analytical per-formances of the Cobas 6800 CT/NG assay (C6800) against the Abbottm2000 Real Time CT/NG (m2000) assay for the detection ofC. trachomatisandN. gonorrhoeae.The evalua-tion ofC6800 was performed retrospectively on 714 speci-mens referred to the bacteriology laboratory at Geneva University Hospitals, between November 2017 and March 2018, from general practice and sexual health wards; and prospectively on nine external quality controls for molecular diagnostics (seven from QCMD Glasgow and two from UK NEQAS). We have included all oropharyngeal and anorectal
Received 9 May 2018; Accepted 6 December 2018
Author affiliations:1Bacteriology Laboratory, Division of Laboratory Medicine, Department of Genetics, Laboratory Medicine and Pathology, Geneva University Hospitals, 4 rue Gabrielle-Perret-Gentil, 1205 Geneva, Switzerland;2Institute of Microbiology, University of Lausanne & University Hospital Center, Lausanne, Switzerland;3Laboratory of Virology, Division of Laboratory Medicine, Department of Genetics, Laboratory Medicine and Pathology, Geneva University Hospitals, 4 rue Gabrielle-Perret-Gentil, 1205 Geneva, Switzerland;4Division of Laboratory Medicine, Department of Genetics, Laboratory Medicine and Pathology, Geneva University Hospitals, Geneva, Switzerland; 5Laboratory Medicine Division, Department of Medical
SHORT COMMUNICATION
Cherkaouiet al.,Journal of Medical Microbiology DOI 10.1099/jmm.0.000909
specimens referred to our routine laboratory during the specified study period.
Discordant specimens were sent to the Institute of Microbi-ology, University of Lausanne, Switzerland and retested by an independent set of real-time PCR assays previously pub-lished [9, 10]. Urine and swab specimens were collected using the Abbott multi-Collect Specimens Collection KIT.
Specimens were transported in the multi-Collect Specimens Transport Tube. Afterm2000 analysis according to manu-facturer’s instructions, the multi-Collect Specimens Trans-port Tubes were stored at 4C until testing byC6800. For C6800 analysis, all the stored specimens were analysed by spiking 2 ml of urine and 600 µL of swabs specimens
transported in the Abbott multi-Collect Specimens Trans-port Tubes into cobas PCR Media tube containing 4.3 ml of transport medium, and tested according to manufacturer’s instructions. Among specimens (including the nine external quality controls) analysed in the m2000 and that met the criteria for supplementary testing byC6800, 19.6 % (142 of 723) were positive forC. trachomatis,4.7 % (33 of 723) were positive forN. gonorrhoeae,while 0.6 % (4 of 723) were pos-itive for both pathogens (Table 1).
Seventy-four percent (530 of 714) of the samples were from females, and 26 % (184 of 714) were from males. The median age of the patients at the time of testing was 31 years with a range from 12 to 80 years.
For C. trachomatis, the sensitivity of C6800 compared to m2000 was 100 %, the specificity was 99.1 %, the negative predictive value (NPV) was 100 %, and the positive predic-tive value (PPV) was 96.7 %. The kappa score forC6800 was 0.979 (95 % confidence interval [CI], 96.0 to 99.7 %). ForN.
gonorrhoeae, the sensitivity of C6800 compared to m2000 was 100 %, the specificity was 99.7 %, the NPV was 100 %, and the PPV was 94.9 %. The kappa score for C6800 was 0.972 (95 % CI, 93.4 to 100 %) (Table 2). One of six discrep-ant C6800 specimens (m2000 negative or indeterminate/
C6800 positive) tested by an independent real-time PCR assay at the Institute of Microbiology, University of Lau-sanne, was confirmed positive forC. trachomatis.
Taking into account all available bacteriological informa-tion, two discrepant specimens (m2000 negative or indeter-minate/C6800 positive) were considered negative even though the two patients had, at the time of testing, another specimen positive with the same pathogen (Table 3).
The recent study conducted by Marlowe et al., on over 12 000 urogenital and extragenital specimens in Germany and the United States, documents the accuracy ofC6800 to detectC. trachomatis and N. gonorrhoeae.Among urogeni-tal, oropharyngeal, and anorectal specimens, there were 125
Table 1. Specimens used for the evaluation of the analytical performances of the Cobas 6800 CT/NG assay against the Abbott m2000 Real Time CT/NG assay, for the detection ofC. trachomatisand N. gonorrhoeae
Specimen type No. of specimens tested including 9 external
Urethral swab 4 2 2
Total 723 146 37
Table 2.Comparison of Cobas 6800 CT/NG assay to Abbottm2000 Real Time CT/NG assay for the detection ofC. trachomatis and N. gonorrhoeae Test No. of specimens
tested
No. of specimens with indicated results 146 572 0 5 100 (97.5–100) 99.1 (98–99.7) 100 (100) 96.7 (92.4–
98.6) M,m2000 (reference method) result; C,C6800 (comparative method) result;+, positive result;-, negative result; CI, 95 % confidence interval for over-all agreement of the reference method and the comparative method; NPV, negative predictive value; PPV, positive predictive value.
Cherkaouiet al.,Journal of Medical Microbiology
C. trachomatis and42N. gonorrhoeaediscrepant specimens (C6800 positive andC4800 negative). Sequencing confirmed C6800 positive C. trachomatis results for 75 of 125 (60 %) specimens and positiveN. gonorrhoeaeresults for 35 of 42 (83 %) specimens [3].
The discordant quality control (QCMD) Glasgow/CTDNA 18C1-05 (m2000 indeterminate/C6800 positive) was con-firmed positive by the independent real-time PCR assay for C. trachomatis(257 copies per ml). After discordance analy-sis, the specificities forC6800 forC. trachomatisandN. gon-orrhoeaeincreased to 99.5 % (95 % CI, 98.5 to 99.9 %) and 99.9 % (95 % CI, 99.2 to 100 %), respectively.
This study has one limitation related to the fact that the specimens included in the evaluation of C6800 were not placed directly into the manufacturer’s transport media (cobas PCR Media tube containing transport medium) but were shipped in Abbott multi-Collect Specimens Collection KIT.
This study demonstrated thatC6800 performed with great accuracy when detecting C. trachomatis and N.
gonorrhoeae.
Conflicts of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Table 3.DiscrepantC6800 specimens (m2000 negative or indeterminate/C6800 positive)
Sample Specimen type Abbottm2000 assay RocheC6800 assay Real-time PCR (CHUV) Comments C.
NEG NEG NEG POS(39.99) NEG NEG The patient had urethral and urine
samples positive forN.
gonorrhoeaeat the time of testing
2 Self- or
clinician-collected vaginal swab
NEG NEG NEG POS(39.35) NEG NEG
3 First-catch urine sample
NEG POS POS(41.55) POS NEG POS(1100
copies/mL) 4 Oropharyngeal
(throat) swab
NEG POS POS(37.99) POS POS(260
copies/mL)
POS(7900 copies/mL) 5 First-catch
urine sample
Indeterminate NEG POS(37.98) NEG NEG NEG The patient had cervical swab
positive forC. trachomatisat the time of testing
6 First-catch urine sample
Indeterminate NEG POS(40.69) NEG NEG NEG
7 First-catch urine sample
Indeterminate NEG POS(34.13) NEG POS(257
copies/mL)
NEG Quality Control for Molecular Diagnostics (QCMD) Glasgow/
CTDNA 18C1-05
Discordant specimens were sent to Institute of Microbiology, University of Lausanne, Switzerland (CHUV) and retested by an independent set of real-time PCR assays previously published. Indeterminate,C. trachomatissample still with a cycle number beyond the assay cut-off after retesting. The results were assessed also with additional bacteriological information as described in the Comments
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Cherkaouiet al.,Journal of Medical Microbiology
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