title: Comparison of the population excess fraction of Chlamydia trachomatis infection on pelvic inflammatory disease at 12-months in the presence and absence of chlamydia testing and treatment: Systematic review and retrospective cohort analysis.
abstract: BACKGROUND
  The impact of Chlamydia trachomatis (chlamydia) control on the incidence of pelvic inflammatory disease (PID) is theoretically limited by the proportion of PID caused by chlamydia. We estimate the population excess fraction (PEF) of treated chlamydia infection on PID at 12-months in settings with widespread chlamydia control (testing and treatment) and compare this to the estimated PEF of untreated chlamydia.
  
  
  METHODS
  We used two large retrospective population-based cohorts of women of reproductive age from settings with widespread chlamydia control to calculate the PEF of treated chlamydia on PID at 12-months. We undertook a systematic review to identify further studies that reported the risk of PID in women who were tested for chlamydia (infected and uninfected). We used the same method to calculate the PEF in eligible studies then compared all estimates of PEF.
  
  
  RESULTS
  The systematic review identified a single study, a randomised controlled trial of chlamydia screening (POPI-RCT). In the presence of testing and treatment <10% of PID at 12-months was attributable to treated (baseline) chlamydia infections (Manitoba: 8.86%(95%CI 7.15-10.75); Denmark: 3.84%(3.26-4.45); screened-arm POPI-RCT: 0.99%(0.00-29.06)). In the absence of active chlamydia treatment 26.44%(11.57-46.32) of PID at 12-months was attributable to untreated (baseline) chlamydia infections (deferred-arm POPI-RCT). The PEFs suggest that eradicating baseline chlamydia infections could prevent 484 cases of PID at 12-months per 100,000 women in the untreated setting and 13-184 cases of PID per 100,000 tested women in the presence of testing and treatment.
  
  
  CONCLUSIONS
  Testing and treating chlamydia reduced the PEF of chlamydia on PID by 65% compared to the untreated setting. But in the presence of testing and treatment over 90% of PID could not be attributed to a baseline chlamydia infection. More information is needed about the aetiology of PID to develop effective strategies for improving the reproductive health of women.
authors.affiliation: Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, United Kingdom.
authors.forename: Bethan
authors.identifier: http://orcid.org/0000-0002-6585-7641
authors.initials: B
authors.lastname: Davies
authors.affiliation: School of Veterinary Science, University of Bristol, Langford, Bristol, United Kingdom.
authors.forename: Katy M E
authors.initials: KM
authors.lastname: Turner
authors.affiliation: Department of Community Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Stella
authors.initials: S
authors.lastname: Leung
authors.affiliation: Department of Community Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada.|Epidemiology & Surveillance, Public Health Branch, Manitoba Health Healthy Living and Seniors, Winnipeg, Manitoba, Canada.
authors.forename: B Nancy
authors.initials: BN
authors.lastname: Yu
authors.affiliation: Department of Microbiology and Infection Control, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: Maria
authors.initials: M
authors.lastname: Frølund
authors.affiliation: Department of Infectious Diseases, Hvidovre University Hospital, Hvidovre, Denmark.|Institute of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Benfield
authors.affiliation: Department of Community Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: James
authors.initials: J
authors.lastname: Blanchard
authors.affiliation: Institute of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark.|Department of Clinical Microbiology, Hvidovre University Hospital, Hvidovre, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Westh
authors.affiliation: Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, United Kingdom.
authors.forename: Helen
authors.initials: H
authors.lastname: Ward
mesh_terms: D002690:Chlamydia Infections / Q000150:complications / Q000175:diagnosis* / Q000453:epidemiology; D002692:Chlamydia trachomatis / Q000302:isolation & purification*; D002986:Clinical Trials as Topic; D005260:Female; D006801:Humans; D000292:Pelvic Inflammatory Disease / Q000150:complications / Q000175:diagnosis* / Q000453:epidemiology; D015995:Prevalence; D012189:Retrospective Studies; D012306:Risk