Chlamydia trachomatis (C. trachomatis) prevalence has been reported to be increasing. Whether this is a true increase over time or confounded by increases in testing and/or use of more sensitive assays is to be determined.

Materials and Methods
One laboratory service has been detecting C. trachomatis for the past 30 years within the Royal Women’s Hospital Melbourne. We conducted a retrospective audit of records over the period 1986–2016 from a clinic population routinely offered chlamydia screening. These were women presenting for family planning advice (termination of pregnancy, intrauterine device insertion or considered at high risk), who underwent chlamydia testing in the context of various diagnostic assays used over this time period. Assays utilised included culture, enzyme immunoassay (EIA), DNA probe, and nucleic acid amplification testing (NAAT). Non‐parametric test for trend was used to determine significant differences between prevalence estimates across ordered groups. Least squares regression was conducted to describe a linear trend matching known data points.

Overall, there was no significant change for chlamydia prevalence which was 2.2%, in the 30‐year study period (P = 0.7). Over time diagnostic assays changed from culture, to EIA, DNA probe, to the more sensitive NAAT. The bulk of the positives were in women under 25 years of age (57%).

Chlamydia prevalence has been stable over 30 years, remaining a problem in young women. Screening for those at risk needs underscoring in a national sexual health program.