Exploration of gender differences of Chlamydia trachomatis infection amongst young people reveals limitations of using sexual histories to assess risk in high-prevalence areas.

In England, chlamydia positivity in young men occurs at a slightly older age group (20-24 years) than positivity among young women (16-20 years) but total rates of infection among the population aged under 25 years are similar. Where there is variation, explanations often focus on individual sexual risk behaviours. We aimed to explore the extent to which variations in chlamydia positivity could be explained by reasons for attendance and sexual behaviour at a sexual health clinic in a high-prevalence area of England. Data routinely collected during clinic appointments were extracted retrospectively from the medical records of 952 clinic users (634 women) aged 16 to 24. We tested for associations with chlamydia positivity using the Chi square statistic and multiple logistic regression for men and women separately; 19.5% of men tested positive (95% CI: 15.1-23.8) compared to 11.5% of women (95% CI: 9.0-14.0). Reporting a partner with symptoms or a sexually transmitted infection diagnosis was significantly associated with a positive diagnosis (Men OR: 3.14, 95% CI: 1.5-6.25; Women OR: 3.78, 95% CI: 1.83-7.83). All other reasons for attendance and all sexual behaviour variables were not significantly associated with a positive diagnosis. Differences in chlamydia positivity between men and women attending this service cannot be explained by individual sexual behaviours found to be associated with higher risk of infection in national studies. Our findings question the utility of individual behavioural data routinely collected during clinic appointments for predicting risk of sexually transmitted infections in high-prevalence areas.