Background Notifications for Sexually transmitted infections cannot be used to measure changing incidence or prevalence of infection if a substantial proportion of infections are asymptomatic and screening rates are low. This analysis aimed to determine whether chlamydia positivity among heterosexual men and chlamydia and gonorrhoea positivity among men who have sex with men (MSM) have changed over time after adjusting for sexual risk.

Methods Computerised records for men attending a large sexual health clinic between 2002 and 2009 were analysed. Urethral chlamydia positivity in all men, and anal chlamydia and anal and pharyngeal gonorrhoea positivity in MSM was calculated. Logistic regression was used to assess change in positivity over time adjusting for demographic, clinical, and sexual behavioural risk factors. Testing data from the Victorian Infectious Diseases Reference Laboratory (VIDRL) was also included to supplement the MSHC data.

Results 17769 heterosexual men and 8328 MSM tested for chlamydia and 7133 MSM tested for gonorrhoea between 2002 and 2009. In heterosexual men, 7.37% (95% CI 6.99 to 7.77) were chlamydia positive with positivity increasing by 4% per year (OR 1.04, 95% CI 1.01 to 1.07) in multivariate analysis. In MSM, 3.70% (95% CI 3.30 to 4.14) had a urethral chlamydia infection and 5.36% (95% CI 4.82 to 5.96) had an anal chlamydia infection, but positivity did not change over time. In MSM, 3.05% (95% CI 2.63 to 3.53) tested positive for anal gonorrhoea and 1.83% (95% CI 1.53 to 2.18) for pharyngeal gonorrhoea. Univariate analysis found anal gonorrhoea positivity had decreased (OR 0.93; 95% CI 0.87 to 1.00), but after multivariate analysis adjusting for sexual risk there was no change. Urethral gonorrhoea cases in MSM as a percentage of all MSM tested for gonorrhoea also fell (p<0.001). The gonorrhoea and chlamydia infection rates in MSM from VIDRL supported our clinic findings showing significant declines in anal and pharyngeal gonorrhoea infections over time and a less marked, but also significant, decline in anal chlamydia; however only univariate analysis was possible.

Conclusions These data suggest that chlamydia prevalence in heterosexual men is rising and chlamydia and gonorrhoea prevalence among MSM is stable or declining. High STI testing rates among MSM in Australia may explain differences in STI trends between MSM and heterosexual men.