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No widespread dissemination of Chlamydia trachomatis diagnostic-escape variants and the impact of Neisseria gonorrhoeae positivity on the Aptima Combo 2 assay

Cole, MJ; Davis, GS; Fifer, H; Saunders, JM; Unemo, M; Hadad, R; Roberts, DJ; ... Folkard, K; + view all (2021) No widespread dissemination of Chlamydia trachomatis diagnostic-escape variants and the impact of Neisseria gonorrhoeae positivity on the Aptima Combo 2 assay. Sexually Transmitted Infections 10.1136/sextrans-2021-054988. (In press). Green open access

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Abstract

OBJECTIVES: A Finnish Chlamydia trachomatis (CT) new variant was detected in 2019 that escaped detection in the Hologic Aptima Combo 2 (AC2) assay due to a C1515T mutation in the CT 23S rRNA target region. Reflex testing of CT-negative/CT-equivocal specimens as well as those positive for Neisseria gonorrhoeae (NG) with the Hologic Aptima CT (ACT) assay was recommended to identify any CT variants. METHODS: From June to October 2019, specimens with discrepant AC2/ACT CT results were submitted to Public Health England and screened for detectable CT DNA using an inhouse real-time (RT)-PCR. When enough DNA was present, partial CT 23S rRNA gene sequencing was performed. Analysis of available relative light units and interpretative data was performed. RESULTS: A total of 317 discordant AC2/ACT specimens were collected from 315 patients. Three hundred were tested on the RT-PCR; 53.3% (n=160) were negative and 46.7% (n=140) were positive. Due to low DNA load in most specimens, sequencing was successful for only 36 specimens. The CT 23S rRNA wild-type sequence was present in 32 specimens, and two variants with C1514T or G1523A mutation were detected in four specimens from three patients. Of the discordant specimens with NG interpretation, 36.6% of NG-negative/CT-negative AC2 specimens had detectable CT DNA on the inhouse RT-PCR vs 53.3% of NG-positive/CT-negative specimens. CONCLUSIONS: No widespread dissemination of AC2 diagnostic-escape CT variants has occurred in England. We however identified the impact of NG positivity on the discordant AC2/ACT specimens; a proportion appeared due to NG positivity and the associated NG signal, rather than any diagnostic-escape variants or low DNA load. Several patients with gonorrhoea may therefore receive false-negative AC2 CT results. Single diagnostic targets and multiplex diagnostic assays have their limitations such as providing selection pressure for escape mutants and potentially reduced sensitivity, respectively. These limitations must be considered when establishing diagnostic pathways.

Type: Article
Title: No widespread dissemination of Chlamydia trachomatis diagnostic-escape variants and the impact of Neisseria gonorrhoeae positivity on the Aptima Combo 2 assay
Location: England
Open access status: An open access version is available from UCL Discovery
DOI: 10.1136/sextrans-2021-054988
Publisher version: http://dx.doi.org/10.1136/sextrans-2021-054988
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher's terms and conditions.
Keywords: Chlamydia trachomatis, Neisseria gonorrhoeae, chlamydia infections, molecular diagnostic techniques, nucleic acid amplification techniques
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Population Health Sciences > Institute for Global Health
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Population Health Sciences > Institute for Global Health > Infection and Population Health
URI: https://discovery.ucl.ac.uk/id/eprint/10137437
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