American Journal of Epidemiology Advance Access originally published online on May 23, 2008
American Journal of Epidemiology 2008 168(2):188-196; doi:10.1093/aje/kwn103
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ORIGINAL CONTRIBUTIONS |
A Longitudinal Study of Vaginal Douching and Bacterial Vaginosis—A Marginal Structural Modeling Analysis
1 Department of Epidemiology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD
2 Division of Epidemiology, Statistics and Prevention Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD
3 Department of Obstetrics and Gynecology, School of Medicine, University of Alabama at Birmingham, Birmingham, AL
4 Division of Infectious Diseases, School of Medicine, University of Alabama at Birmingham, Birmingham, AL
5 Division of Infectious Diseases, School of Medicine, Johns Hopkins University, Baltimore, MD
6 Department of Biostatistics, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD
Correspondence to Dr. Rebecca Brotman, Division of Infectious Diseases, Johns Hopkins Bayview Medical Center, 4940 Eastern Avenue, B-3 North, Baltimore, MD 21224 (e-mail: rbrotman{at}jhsph.edu).
Received for publication September 12, 2007. Accepted for publication March 24, 2008.
The etiology of bacterial vaginosis is unknown, and there are no long-term therapies for preventing this frequently recurring condition. Vaginal douching has been reported to be associated with bacterial vaginosis in observational studies. However, this association may be due to confounding by indication—that is, confounding by women douching in response to vaginal symptoms associated with bacterial vaginosis. The authors used marginal structural modeling to estimate the causal effect of douching on bacterial vaginosis risk while controlling for this confounding effect. In 1999–2002, nonpregnant women (n = 3,620) were recruited into a prospective study when they visited one of 12 public health clinics in Birmingham, Alabama, for routine care. Participants were assessed quarterly for 1 year. Bacterial vaginosis was based on a Nugent's Gram stain score of 7 or higher. Thirty-two percent of participants douched in every study interval, and 43.0% never douched. Of the 12,349 study visits, 40.2% were classified as involving bacterial vaginosis. The relative risk for regular douching as compared with no douching was 1.21 (95% confidence interval: 1.08, 1.38). These findings indicate that douching confers increased risk of disruption of vaginal flora. In the absence of a large randomized trial, these findings provide the best evidence to date for a risk of bacterial vaginosis associated with douching.
confounding factors (epidemiology); epidemiologic methods; longitudinal studies; models, structural; vaginal douching; vaginosis, bacterial
Abbreviations: CI, confidence interval; MICE, multivariate imputation by chained equations
This version reflects a correction to the author line