No indication of Swedish Chlamydia trachomatis variant among STI clinic visitors in Amsterdam

Is there evidence of the new variant Chlamydia trachomatis in the United States?

A specific real-time polymerase chain reaction followed by melt curve analysis was developed for the detection of the Swedish variant (nvCT) strain of Chlamydia trachomatis (CT). Surveillance was performed on 476 CT-positive clinical specimens obtained from 15 laboratories around the United States using nucleic acid amplification test assays, which would not miss the nvCT. All were negative for nvCT; thus, there is no evidence of the nvCT in the United States.

[The Swedish Chlamydia mutant nvC trachomatis in Norway]

BACKGROUND

A mutant Chlamydia trachomatis variant (nvC trachomatis) has made it more difficult to diagnose chlamydia in Sweden. The proportion of nvC trachomatis has varied between Swedish counties (25-80 %) in the period 2006-07. Our goal has been to monitor nvC trachomatis among our patients from January 2007 and up to July 2008.

MATERIAL AND METHODS

In this time period, all C trachomatis samples at Fürst Medical Laboratory, Norway were analyzed twice. Cobas TaqMan 48 (Roche Diagnostics) was used to detect C trachomatis in isolated DNA and real-time PCR methods developed by us were used to both detect and verify nvC trachomatis.

RESULTS

61 patients of 23 726 patients were identified as carriers of nvC trachomatis. The proportion of C trachomatis carriers who were positive for nvC trachomatis increased from 1.0 % in the first quarter of 2007 to 3.2 % in the second quarter of 2008.

INTERPRETATION

Our results show a slow but steady increase in the proportion of nvC trachomatis positive tests. As compared to previous rates reported in Sweden (25-80 %), the occurrence of nvC trachomatis in our data is low. The epidemiology of this chlamydia mutant contributes to the understanding of mechanisms for spread of sexually transmitted infections and emphasize that you only find what you are looking for.

No evidence of the Chlamydia trachomatis variant in the UK

OBJECTIVES

The discovery of a variant strain of Chlamydia trachomatis (Ct) in Sweden has raised awareness of its possible undetected spread in the UK. The assays that fail to detect this variant are widely used in this country. This study aimed to determine if this variant is circulating in the UK.

METHOD

1,680 genital specimens tested negative by the Roche assays were retested by Aptima Combo2. Discordant results were sequenced to check for the deletion variant.

RESULTS

Of 1,680 specimens tested, 29 were candidates for sequencing: 16 were negative for the variant, 11 failed to amplify, and 2 were lost.

DISCUSSION

No Ct deletion variants were found in the UK. If it is circulating, then the prevalence is low (0-0.77%), but even a low level cannot be ignored. The system we describe is simple and suitable for rapid response and phasing of surveillance to match an unknown level of threat if other variants emerge.

Chlamydia trachomatis variant not detected by plasmid based nucleic acid amplification tests: molecular characterisation and failure of single dose azithromycin

OBJECTIVE

To characterise a Chlamydia trachomatis variant strain from a patient with non-gonococcal urethritis (NGU) whose first void urine (FVU) displayed discrepant Ctrachomatis test results and describe the clinical response to treatment.

METHODS

The FVU specimen was assayed with an immune based Chlamydia Rapid Test (CRT) and various nucleic acid amplification tests (NAATs) to establish C trachomatis infection. Sequencing of the major outer membrane protein gene (omp1 also known as ompA) was undertaken to identify the serovar of the variant strain. Polymerase chain reaction (PCR) analysis was also conducted to determine whether the strain harboured deletions in the cryptic plasmid or was plasmid free.

RESULTS

The FVU specimen was strongly reactive in CRT but negative with the plasmid based Amplicor PCR (Roche) and ProbeTec ET (Becton-Dickinson) assays. However, NAATs for 16S RNA (Aptima Combo 2, GenProbe), omp1 (RealArt CT PCR, Artus and in-house NAATs) or the outer membrane complex B protein gene (omcB) established C trachomatis infection. Sequencing of omp1 showed that the variant belonged to serovar I. PCR analysis indicated that the variant was plasmid free. The patient did not respond to single dose azithromycin treatment but subsequently responded to a course of doxycycline.

CONCLUSIONS

A pathogenic plasmid free C trachomatis variant was identified. Clinicians should be alerted to the possibility of undetected C trachomatis infection caused by such variants and the potential of azithromycin failure in patients with recurrent chlamydial NGU. The occurrence of this variant is rare and should not form the basis for judgment of the performance or usefulness of plasmid based NAATs for C trachomatis detection.