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Chlamydia trachomatis re-infections in a population-based cohort of women
  1. Bette Liu1,
  2. Rebecca Guy1,
  3. Basil Donovan1,2,
  4. John M Kaldor1
  1. 1The Kirby Institute, Faculty of Medicine, University of New South Wales, Sydney, New South Wales, Australia
  2. 2Sydney Sexual Health Centre, Sydney Hospital, Sydney, Australia
  1. Correspondence to Dr Bette Liu, The Kirby Institute, Faculty of Medicine, University of New South Wales, Sydney, NSW 2052, Australia; bliu{at}


Objectives Re-infection with chlamydia may increase subsequent reproductive morbidity in women. The authors sought to identify characteristics associated with re-infection.

Methods A cohort of all women aged 10–49 years with a notification of genital chlamydia in the Australian state of New South Wales during 1999–2008 was defined. Probabilistic linkage was used to identify women with repeat notifications in the same period. The risk of repeat notification was examined according to age and other characteristics using proportional hazards regression.

Results Among 40 936 women in the cohort, 3236 had at least one repeat chlamydia notification over an average of 3.5 years of follow-up. The incidence of repeat notification was greatest in the first year after index notification (4.5 per 100 person-years) and decreased thereafter. The RR of repeat notification increased by 8% (95% CI 7% to 9%) for each year decrease in age. Compared with women aged 20–21 years at index chlamydia notification, women aged <16 years were twice as likely to have a repeat notification (adjusted HR 2.12, 95% CI 1.75 to 2.56), while women aged 26–27 years were half as likely (adjusted HR 0.53, 95% CI 0.43 to 0.66). Year of index notification, parity and concurrent or past gonorrhoeal infection were also significantly associated with the risk of repeat notification, but socioeconomic status and area of residence were not.

Conclusions Younger age is a strong predictor of chlamydia re-infection in women. The results support targeting interventions to prevent re-infections to very young women.

  • Chlamydia
  • re-infection
  • repeat infection
  • record linkage
  • chlamydia infection
  • epidemiology (general)
  • gynaecology
  • hepatitis
  • hormonal contraception
  • epidemiology (clinical)
  • bacterial infection
  • prevention
  • primary care
  • C trachomatis
  • primary HIV infection

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  • Funding This work was supported by the Australian National Health and Medical Research Council (NHMRC) grant numbers 568971 and 573122. The funder had no input into the study design, analysis, interpretation, writing nor decision to submit for publication. BL, RG, BD and JK are supported by NHMRC fellowships.

  • Competing interests None.

  • Ethics approval Ethics approval was provided by NSW Population and Health Services Research Ethics Committee and University of New South Wales Human Research Ethics Committee.

  • Provenance and peer review Not commissioned; externally peer reviewed.