Chlamydia is the most commonly notified infection in Australia. Prevention strategies should be informed by routine data on at-risk populations.

We calculated chlamydia positivity and correlates of infection using multivariable logistic regression for data collected between April 2006 and June 2009.

Chlamydia positivity was 5.6% in 12233 females, 7.7% in 10316 heterosexual males and 6.2% in 7872 men who have sex with men (MSM). Correlates of chlamydia positivity among females included younger age (odds ratio (OR) 2.27, 95% confidence interval (CI) 1.92-2.69), being born overseas (OR 1.50, 95% CI 1.25-1.82), multiple sex partners in the past year (OR 1.72, 95% CI 1.40-2.11) and inconsistent condom use with regular sex partners (OR 3.44 ,95% CI 1.65-7.20). Sex work was protective for females (OR 0.68, 95% CI 0.53-0.86). Among heterosexual males, correlates of positivity were younger age (OR 1.87, 95% CI 1.62-2.17), being born overseas (OR 1.35, 95% CI 1.16-1.58), symptoms at the time of testing (OR 1.64, 95% CI 1.40-1.92) and multiple sex partners in the past year (OR 1.83, 95% CI 1.46-2.30). Correlates of positivity among MSM were being born overseas (OR 1.23, 95% CI 1.00-1.51), being HIV-positive (OR 1.80, 95%CI 1.32-2.47), and reporting six or more anal sex partners in the past 6 months (OR 4.45, 95% CI 1.37-14.5).

Our analysis identified subgroups at the highest risk of chlamydia in Victoria. These estimates will provide important baseline information to measure the impact of chlamydia control strategies.