Chlamydia trachomatis incidence and re-infection among young women - behavioural and microbiological characteristics

Background: This study aimed to estimate rates of chlamydia incidence and re-infection and to investigate the dynamics of chlamydia organism load in prevalent, incident and re-infections among young Australian women. Methods: 1,116 women aged 16 to 25 years were recruited from primary care clinics in Australia. Vaginal swabs were collected at 3 to 6 month intervals for chlamydia testing. Chlamydia organism load was measured by quantitative PCR. Results: There were 47 incident cases of chlamydia diagnosed and 1,056.34 person years of follow up with a rate of 4.4 per 100 person years (95 CI: 3.3, 5.9). Incident infection was associated with being aged 16 to 20 years [RR = 3.7 (95 CI: 1.9, 7.1)], being employed [RR = 2.4 (95 CI: 1.1, 4.9)] and having two or more new sex partners [RR = 5.5 (95 CI: 2.6, 11.7)]. Recent antibiotic use was associated with a reduced incidence [RR:0.1 (95 CI: 0.0, 0.5)]. There were 14 re-infections with a rate of 22.3 per 100 person years (95 CI: 13.2, 37.6). The median time to re-infection was 4.6 months. Organism load was higher for prevalent than incident infections (