Absence of a Chlamydia trachomatis variant, harbouring a deletion in the cryptic plasmid, in clients of a sexually transmissible infection clinic and antenatal patients in Melbourne.

A Chlamydia trachomatis (CT) variant, harbouring a 377 bp deletion in the cryptic plasmid, recently identified in Europe, has caused false-negative reporting of CT infections by various assays. This report is aimed at identifying whether this variant is present among clients of a sexual health clinic, or antenatal screening patients in Melbourne. Two hundred CT-positive specimens (by BDProbeTec ET assay) from Melbourne Sexual Health Centre (August 2005-November 2006) were tested by COBAS TaqMan 48 PCR assay. Discrepancies were tested by an in-house real-time (Re-Ti) polymerase chain reaction (PCR) assay, amplifying a 274-bp region of the omp1 gene. Additionally, 1,071 consecutive specimens from antenatal screening patients at the Royal Women's Hospital (December 2006-April 2007) were tested by COBAS TaqMan 48 and omp1 Re-Ti PCR. The CT variant was not detected among the 200 CT-positive specimens (95% confidence interval 0-2.3%). Three tested CT-negative by COBAS TaqMan 48, omp1 Re-Ti PCR and CT mutant-specific PCR, suggesting sample degradation or differential assay sensitivity. Of the 1,071 antenatal screening specimens, 56 tested CT-positive and 1,015 CT-negative by COBAS TaqMan 48. All of the CT-negatives tested negative by omp1 Re-Ti PCR (95% confidence interval 0-0.5%), with 51 of 56 CT-positives testing positive. These findings show there were no CT variants among attendees of a Melbourne sexual health clinic, nor among antenatal screening patients. It is likely that the variant strain has not yet entered circulation in these populations. However, given the current upsurge in urogenital CT-infections, continued surveillance is necessary to ensure timely detection of this variant, should it be introduced into the population.