title: Estimating chlamydia re-infection rates: an empirical example.
abstract: OBJECTIVE
  Chlamydia re-infection data are used to inform and evaluate chlamydia control programmes. We quantitatively investigated the effect of denominator selection on estimating re-infection rates and trends.
  
  
  METHODS
  Using data on women aged 15-44 years enrolled in Group Health Cooperative (GH), a Pacific Northwest health plan, annual chlamydia re-infection rates from 1998 to 2006 were calculated. Three different denominators were compared using person-years contributed by: (1) all women; (2) women with a prior documented chlamydial infection regardless of whether they were retested; and (3) women with a prior chlamydial infection who were retested within 14 months.
  
  
  RESULTS
  From 1998 to 2006, among all women 15-44 years enrolled in GH, re-infection rates increased from 64 to 149 cases per 100 000 person-years. Among women with a prior infection, rates decreased from 10 857 to 8782 cases per 100 000 person-years. Among women with a prior infection who were retested, rates increased from 29 374 to 42 475 cases per 100 000 person-years.
  
  
  CONCLUSIONS
  Using the same dataset, we demonstrate that it is possible to tell three different stories about the magnitude of rates and trends in chlamydia re-infection among women by using different denominators. All of these strategies have limitations, but restricting the denominator to women with a prior infection who are retested may best represent the population at-risk for re-infection. Still, rates do not account for additional factors influencing the number of re-infections diagnosed, including screening coverage and changes in test technology. Caution is needed in examining and comparing re-infection data.
authors: Division of STD Prevention, Centers for Disease Control and Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, Atlanta, GA, USA. igf0@cdc.gov
authors: Elizabeth A
authors: EA
authors: Torrone
authors: Catherine L
authors: CL
authors: Satterwhite
authors: Delia
authors: D
authors: Scholes
authors: Onchee
authors: O
authors: Yu
authors: Stuart
authors: S
authors: Berman
authors: Thomas A
authors: TA
authors: Peterman
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D002690:Chlamydia Infections / Q000453:epidemiology* / Q000517:prevention & control; D002692:Chlamydia trachomatis / Q000302:isolation & purification*; D005260:Female; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D008403:Mass Screening; D015233:Models, Statistical; D015205:Northwestern United States / Q000453:epidemiology; D011634:Public Health; D055502:Secondary Prevention; D018571:Sentinel Surveillance
keywords: Bacterial Infection; Chlamydia Infection; Surveillance