To describe trends in chlamydia positivity from 2007 to 2011 among heterosexual people tested for chlamydia at selected clinics that provide services to people at high risk in Victoria, Australia.

The Victorian Primary Care Network for Sentinel Surveillance is a prospective system that collates pathology results from laboratories and demographic and behavioural data from a questionnaire.

Two sexual health clinics and six other primary care clinics that target young people and women at high risk.

All clients tested for chlamydia at sentinel clinics. Individuals aged less than 16 years, sex workers, or those reporting any same-sex sexual partners in the past 12 months were excluded from the analysis.

Chlamydia positivity trends were assessed using three-level random-effects Poisson regression, with clinic and subject treated as nested random factors. Models were offset for total number of tests and adjusted for relevant covariates.

Between 2007 and 2011, chlamydia positivity among 31 682 tests in women increased from 5.1% to 6.3%, and positivity among 23 771 tests in men increased from 7.4% to 8.2%. Adjusting for age, country of birth, number of sex partners, condom use, and presence of symptoms, chlamydia positivity increased between 2007 and 2011 significantly among women (incidence rate ratio [IRR], 1.29; 95% CI, 1.11-1.50) and non-significantly among men (IRR, 1.07; 95% CI, 0.92-1.23). Over time, a decrease in reported inconsistent condom use was also observed in both men and women; however, men became more likely to report more than one partner in the past year.

We identified a concerning increase in chlamydia positivity over time, particularly among young women.