To estimate the population attributable risk (PAR) for Chlamydia trachomatis infection in young men and women in Sydney, Australia.
Multivariate logistic regression was used to examine the association between demographic, sexual behaviour and other potential risk factors and chlamydia positivity in young (≤30 years) heterosexual international travellers (backpackers) and Australian residents attending a sexual health clinic. Point and interval estimates of PAR were calculated to quantify the proportion of chlamydia infections that can theoretically be prevented if a combination of risk factors is eliminated from a target population.
In males, the PAR associated with inconsistent condom use in the past 3 months was 65% (95% CI 56% to 71%) in backpackers compared to 50% (95% CI 41% to 56%) in non-backpackers and the PAR associated with reporting three or more female sexual partners in the past 3 months was similar between male backpackers and non-backpackers (33% (95% CI 28% to 40%) and 36% (95% CI 32% to 41%), respectively). In females, the PAR associated with inconsistent condom use in the past 3 months was 51% (95% CI 42% to 59%) in backpackers compared to 41% (95% CI 31% to 51%) in non-backpackers, and the PAR associated with reporting three or more male sexual partners in the past 3 months was 14% (95% CI 11% to 18%) in backpackers compared to 30% (95% CI 25% to 37%) in non-backpackers.
These findings suggest that the largest number of chlamydia infections could be avoided by increasing condom use, particularly in backpackers. Reporting multiple partners was also associated with a large proportion of infections and the risk associated with this behaviour should be considered in health promotion strategies.
Risk factors for chlamydia infection were determined among young, heterosexual backpackers and Australian residents.
A novel statistical methodology was used to investigate the potential impact of eliminating risk factors on chlamydia infection at a population level.
Results suggest that the majority of the chlamydia infections could be avoided by increased condom use, particularly among backpackers.
Multiple sex partners in past 3 months was also associated with a high proportion of chlamydia infections at the population level.
Strengths and limitations of this study
This is the first study to investigate the potential impact of sexual risk behaviours for chlamydia infection at the population level.
The study population was sexual health clinic attendees who are likely to be at higher risk for chlamydia infection compared to the general population.