Objectives In 2006, a new variant of Chlamydia trachomatis (nvCT) was reported in Sweden. Because of a cryptic plasmid deletion, the nvCT was undetectable in several of the genetic diagnostic systems used worldwide at the time. This study aimed to evaluate whether the nvCT was present in specimens obtained from patients attending the outpatient sexually transmitted infection (STI) clinic at Örebro University Hospital, Örebro, Sweden already in 2002–2003.
Methods In 2012, archival (−20°C freezer) urogenital specimens (2002 (n=1083) and in 2003 (n=1143)) obtained from men (2002 (n=398) and 2003 (n=486)) and women (2002 (n=301) and 2003 (n=408)) were analysed with Cobas TaqMan CT test V.2.0. All C trachomatis positive specimens were subsequently examined using a duplex PCR assay that simultaneously detects the deletion on the nvCT cryptic plasmid and the ompA gene of C trachomatis genotype E.
Results In total, 68 patients (9.7%) in 2002 and 61 (6.8%) in 2003 were C trachomatis positive. The duplex PCR assay identified 26 C trachomatis genotype E positive patients in 2002 (38%) and 25 in 2003 (41%). No nvCT was found in 2002, but one specimen obtained from a 23-year-old man in June 2003 was positive for the nvCT.
Conclusions The nvCT was present as early as 2003 in Örebro County, Sweden, which concurs with previously reported statistical estimations of its emergence. Accordingly, the nvCT spread undetected for at least 3 years, explaining the high proportion (38%) in Örebro County when it was first detected in late 2006.
- Chlamydia Trachomatis
- Epidemiology (General)
Statistics from Altmetric.com
In October 2006, a new variant of Chlamydia trachomatis (nvCT) was reported in Sweden.1 The nvCT has a 377 bp deletion on the cryptic plasmid. This cryptic plasmid deletion includes the DNA target sequences for the earlier versions of nucleic acid amplification tests (NAATs) from Roche Diagnostics and Abbott Laboratories, which at the time were widely used internationally.1 Consequently, during several years, thousands of false-negative results were generated across Sweden. In 2008, both Roche Diagnostics and Abbott Laboratories had Conformité Européenne (CE) mark-certified novel dual-target NAATs capable of detecting nvCT.2
Since many years in Sweden, basically all the diagnostic laboratories use only NAATs for diagnosis of CT. However, when nvCT was first reported1 in Örebro County, Sweden, CT specimens were diagnosed using either the Cobas Amplicor CT/NG, Roche Diagnostics, USA (CA PCR) or a highly optimised and quality assured cell culture method (mainly used for cervical specimens on request from submitting physicians). Logistic regression was used in a previous study3 to evaluate the change in the proportion of CT positive tests in 1999–2006 between the two diagnostic methods (CA PCR and cell culture). This statistical estimation indicated that the nvCT may have emerged already before 2002 in Örebro County.3 Previously, there have been no archival collections of samples available for retrospective analysis to verify this estimation on the emergence of the nvCT. Recently, however, a collection of archival urogenital samples obtained from patients attending the outpatient sexually transmitted infection (STI) clinic at Örebro University Hospital in 2002–2003 was found in a −20°C freezer at Örebro University Hospital, Örebro, Sweden.
This study aimed to analyse archival urogenital samples in order to determine whether the nvCT was present as early as 2002–2003 in Örebro County, Sweden.
Material and methods
Urogenital specimens (2002 (n=1083) and 2003 (n=1143)) obtained from men (2002 (n=398) and 2003 (n=486)) and women (2002 (n=301) and 2003 (n=408)) attending the outpatient STI clinic at Örebro University Hospital during May–September 2002 and June–December 2003 were examined. The samples mainly consisted of urine specimens from the men and both urine and cervical specimens from most of the women. All these specimens were collected and stored as part of the routine diagnostics (standard care). All specimens were coded, that is, no detailed patient information was used in this study. The mean age was 28 years in the men (range 17–58 years in 2002, 16–66 years in 2003) and 26 years in the women (range 15–56 years in 2002, 17–58 years in 2003). The specimens were stored at −20°C until analysed in 2012 with Cobas TaqMan CT test V.2.0 (Roche diagnostics, USA) that detects both wild type CT (wtCT) and nvCT. All CT positive specimens were subsequently examined using a duplex PCR that simultaneously detects the nvCT deletion on the cryptic plasmid and the ompA gene of CT serotype E.4 To confirm any nvCT positive specimen, the PCR product was sequenced using previously described cryptic plasmid primers.1
In total, 68 patients (9.7%) in 2002 and 61 patients (6.8%) in 2003 were CT positive. The duplex PCR assay identified 26 CT genotype E positive specimens in 2002 (38%) and 25 in 2003 (41%). No nvCT was found in 2002, but one urine specimen obtained from a 23-year-old man in June 2003 was nvCT positive. Sequencing of partial cryptic plasmid confirmed that this specimen contained the nvCT.
Since its discovery in 2006, the nvCT has been detected in high numbers across Sweden.1–7 Nevertheless, since it could be detected, the proportions have declined and may now be reaching an equilibrium with the wtCT.2 ,4 ,6 ,7 The present study identified a nvCT positive 23-year-old man attending the outpatient STI clinic at Örebro University Hospital in June 2003. Accordingly, in Örebro County, the nvCT was evidently present more than 3 years before the first nvCT report in October 2006,1 which might explain the high nvCT proportion (38%) in the first prevalence study in 2006.5
Surprisingly, although the prevalence of the nvCT in Sweden remains relatively high, it is rarely reported outside the Nordic countries.2 ,7–9 However, knowledge of the presence of the nvCT beyond the Nordic countries is relatively limited because few recent studies have been performed, many laboratories still cannot detect the nvCT, and those that can detect the nvCT rarely distinguish it from the wtCT (UK NEQAS Distribution 2915, issued in October 2011).2 ,7 ,10 Accordingly, because a wider geographic spread of the nvCT cannot be excluded, ideally all laboratories should use NAATs that detect the nvCT.
In conclusion, the nvCT was present as early as 2003 in Örebro County, Sweden, which is in accordance with previously reported statistical estimations on its emergence.3 Consequently, the nvCT was spreading undetected for at least 3 years, explaining the high proportion of the nvCT (38%) in Örebro County when it was first discovered in 2006.
Contributors MJ, with contributions from HF and MU, designed and initiated the study. MJ performed all the laboratory work and initially analysed the data. All coauthors contributed to the writing of the manuscript.
Funding The present study was supported by the Örebro County Council Research Committee (Grant number: OLL-216891) and the Foundation for Medical Research (Grant number: OLL-247571) at Örebro University Hospital, Sweden.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
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