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

Abstract

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 (p<0.01) and for prevalent than re-infections (p<0.01).

Conclusions: Chlamydia is common among young women and a high proportion of women are re-infected within a short period of time, highlighting the need for effective partner treatment and repeat testing. The difference in organism load between prevalent and incident infections suggests prevalent infection may be more important for ongoing transmission of chlamydia.

Figure 1. Algorithm to differentiate between chlamydia re-infection, treatment failure and persistent infection [adapted from Batteiger et al (2009)] .

N/A = Serovar result not available.

Figure 2. Kaplan Meier curve showing proportion remaining uninfected with incident chlamydia infection over time among a cohort of sexually active 16 to 25 year old women.

Figure 3. Kaplan Meier curve showing proportion remaining free from chlamydia re-infection over time among a cohort of sexually active 16 to 25 year old women.

Figure 4. Comparison of chlamydia organism load for prevalent versus incident (excluding re-infection) and re-infection among a cohort of sexually active 16 to 25 year old women [shaded box = interquartile range; black line in box = median value; T bars = range of values].

Figure 5. Comparison of chlamydia organism load at first diagnosis between women who had a negative repeat rest and women who had a positive repeat test of the same serovar among a cohort of sexually active 16 to 25 year old women [shaded box = interquartile range; black line in box = median value; T bars = range of values].