Population attributable fraction of pelvic inflammatory disease associated with chlamydia and gonorrhoea: a cross-sectional analysis of Australian sexual health clinic data.

OBJECTIVES Pelvic inflammatory disease (PID) is an important cause of female infertility and can occur when micro-organisms such as chlamydia or gonorrhoea ascend to the upper genital tract. PID has been used as an outcome measure in chlamydia screening trials; however, few data have quantified the PID burden that could be avoided by preventing chlamydia. We estimated the population attributable fraction (PAF) of PID associated with a current chlamydia or gonorrhoea infection among females 16-49 years attending an Australian sexual health clinic (SHC) (2006-2013). METHODS Using multivariable logistic regression, PAF estimates were adjusted for age and behavioural factors. Two separate analyses were undertaken: one among 'chlamydia-tested' women and one among a subset of chlamydia-tested women who were also tested for gonorrhoea ('chlamydia+gonorrhoea-tested'). A sensitivity analysis using multiple imputation was conducted to assess the impact of missing data on results. RESULTS Among 15 690 chlamydia-tested women, 1279 (8.2%, 95% CI 7.7% to 8.6%) were chlamydia positive, 436 (2.8%, 95% CI 2.5% to 3.0%) had PID diagnosed and the adjusted PAF for chlamydia was 14.1% (95% CI 9.9% to 18.0%). Among the chlamydia+gonorrhoea-tested subset (n=8839), 681 (7.7%, 95% CI 7.2% to 8.3%) tested positive for chlamydia only, 30 (0.3%, 95% CI 0.2% to 0.5%) for gonorrhoea only, 22 (0.2%, 95% CI 0.2% to 0.4%) for chlamydia and gonorrhoea and 419 (4.7%, 95% CI 4.3% to 5.2%) had PID diagnosed. The adjusted PAF was highest for chlamydia only (12.4%, 95% CI 8.4% to 16.2%) compared with gonorrhoea only (0.9%, 95% CI -0.1% to 1.8%) or concurrent infections (1.0%, 95% CI 0.0% to 1.9%). CONCLUSIONS In this high chlamydia prevalence SHC population, eliminating a current chlamydia infection might at most reduce PID by about 14%.