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Obstet Gynecol. 2014 Nov;124(5):954-60. doi: 10.1097/AOG.0000000000000429.

Biological and behavioral risks for incident Chlamydia trachomatis infection in a prospective cohort.

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Department of Pediatrics, Division of Adolescent and Young Adult Medicine, UCSF Benioff Children's Hospital, University of California, San Francisco, San Francisco, California.



To identify biological and behavioral risks for incident Chlamydia trachomatis among a prospective cohort of young women followed frequently.


Our cohort of 629 women from two outpatient sites was seen every 4 months (October 2000 through April 2012) for behavioral interviews and infection testing. C trachomatis was tested annually and any time patients reported symptoms or possible exposure using commercial nucleic acid amplification tests. Analyses excluded baseline prevalent C trachomatis infections. Risk factors for incident C trachomatis were assessed using Cox proportional hazards models. Significant risks (P<.10) from bivariate models were entered in a multivariate model adjusted for four covariates chosen a priori (age, race or ethnicity, condom use, study site). Backward stepwise elimination produced a final parsimonious model retaining significant variables (P<.05) and the four adjustment variables.


The 629 women attended 9,594 total visits. Median follow-up time was 6.9 years (interquartile range 3.2-9.8), during which 97 (15%) women had incident C trachomatis. In the final multivariate model, incident C trachomatis was independently associated with human papillomavirus at the preceding visit (P<.01), smoking (P=.02), and weekly use of substances besides alcohol and marijuana (P<.01) since the prior visit. Among 207 women with available colpophotographs (1,742 visits), cervical ectopy was not a significant risk factor (P range=.16-.39 for ectopy as continuous and ordinal variables).


Novel risks for C trachomatis include preceding human papillomavirus, smoking, and substance use, which may reflect both biological and behavioral mechanisms of risk such as immune modulation, higher-risk sexual networks, or both. Improved understanding of the biological bases for C trachomatis risk would inform our strategies for C trachomatis control.

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