ORIGINAL CONTRIBUTIONS |
Application of the Case-Crossover Design to Reduce Unmeasured Confounding in Studies of Condom Effectiveness
1 National Center for Chronic Disease Prevention and Health Promotion, Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA
2 Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA
3 Department of Epidemiology, School of Public Health, University of Alabama at Birmingham, Birmingham, AL
4 Jefferson County Department of Health, Birmingham, AL
5 National Center for HIV, STD, and TB Prevention, Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, Atlanta, GA
6 Department of Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL
7 Department of Microbiology, School of Medicine, University of Alabama at Birmingham, Birmingham, AL
Correspondence to Dr. Lee Warner, Women's Health and Fertility Branch, Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, 4770 Buford Highway NE (Mailstop K-34), Atlanta, GA 30341 (e-mail: dlw7{at}cdc.gov).
This analysis examined how unmeasured confounding affects estimates of the effectiveness of condoms in preventing sexually transmitted infections. Data were analyzed from a prospective cohort study of 1,122 female sexually transmitted disease clinic patients in Alabama (1992–1995), wherein participants were evaluated for sexually transmitted infections at six 1-month intervals. Associations between condom use and incident gonorrhea and chlamydia infection were compared between case-crossover and cohort analyses. In a case-crossover analysis of 228 follow-up visits ending in gonorrhea/chlamydia ("case intervals") and 743 self-matched follow-up visits not ending in gonorrhea/chlamydia ("noncase intervals") (183 women), consistent condom use without breakage or slippage was associated with significantly reduced risk of infection relative to nonuse (adjusted risk odds ratio = 0.49, 95% confidence interval: 0.26, 0.92). Conversely, a cohort analysis of 245 case intervals and 3,896 noncase intervals (919 women) revealed no significant reduction in infection risk from consistent use of condoms (adjusted risk odds ratio = 0.79, 95% confidence interval: 0.53, 1.17). Dose-response relations between the number of unprotected sex acts and infection were stronger in the case-crossover analysis (p for trend = 0.009) than in the cohort analysis (p for trend = 0.18). These findings suggest that epidemiologic studies confounded by unmeasured differences between condom users and nonusers underestimate condom effectiveness against these infections. The case-crossover method provides an additional technique for reducing unmeasured confounding in studies of condom effectiveness.
chlamydia; confounding factors (epidemiology); contraceptive devices, male; cross-over studies; epidemiologic methods; gonorrhea; HIV infections; sexually transmitted diseases
Abbreviations: ROR, risk odds ratio; STI, sexually transmitted infection
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  E. T. Martin, E. Krantz, S. L. Gottlieb, A. S. Magaret, A. Langenberg, L. Stanberry, M. Kamb, and A. Wald A Pooled Analysis of the Effect of Condoms in Preventing HSV-2 Acquisition Arch Intern Med, July 13, 2009; 169(13): 1233 - 1240. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T A Peterman, L H Tian, L Warner, C L Satterwhite, C A Metcalf, K C Malotte, S M Paul, J M Douglas Jr, and the RESPECT-2 Study Group Condom use in the year following a sexually transmitted disease clinic visit Int J STD AIDS, January 1, 2009; 20(1): 9 - 13. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. Bahamondes, J. Diaz, N. M. Marchi, S. Castro, M. Villarroel, and M. Macaluso Prostate-specific antigen in vaginal fluid after exposure to known amounts of semen and after condom use: comparison of self-collected and nurse-collected samples Hum. Reprod., November 1, 2008; 23(11): 2444 - 2451. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. Warner, D. R. Newman, M. L. Kamb, M. Fishbein, J. M. Douglas Jr, J. Zenilman, L. D'Anna, G. Bolan, J. Rogers, T. Peterman, et al. Problems with Condom Use among Patients Attending Sexually Transmitted Disease Clinics: Prevalence, Predictors, and Relation to Incident Gonorrhea and Chlamydia Am. J. Epidemiol., February 1, 2008; 167(3): 341 - 349. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. J Steiner and W. Cates Are condoms the answer to rising rates of non-HIV sexually transmitted infections? Yes BMJ, January 26, 2008; 336(7637): 184 - 184. [Full Text] [PDF]
|
|
|
|
|
|
M. Macaluso, R. Blackwell, D. J. Jamieson, A. Kulczycki, M. P. Chen, R. Akers, D.-j. Kim, and A. Duerr Efficacy of the Male Latex Condom and of the Female Polyurethane Condom as Barriers to Semen during Intercourse: A Randomized Clinical Trial Am. J. Epidemiol., July 1, 2007; 166(1): 88 - 96. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Hugonnet, A. Villaveces, and D. Pittet Nurse Staffing Level and Nosocomial Infections: Empirical Evaluation of the Case-Crossover and Case-Time-Control Designs Am. J. Epidemiol., June 1, 2007; 165(11): 1321 - 1327. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L Warner, M Macaluso, D Newman, H Austin, D Kleinbaum, M Kamb, J Douglas, C K Malotte, and J M Zenilman Condom effectiveness for prevention of C trachomatis infection. Sex Transm Inf, June 1, 2006; 82(3): 265 - 265. [Full Text] [PDF]
|
|
|
|
 |
|
 A. Wald, A. G.M. Langenberg, E. Krantz, J. M. Douglas Jr, H. H. Handsfield, R. P. DiCarlo, A. A. Adimora, A. E. Izu, R. A. Morrow, and L. Corey The Relationship between Condom Use and Herpes Simplex Virus Acquisition Ann Intern Med, November 15, 2005; 143(10): 707 - 713. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. W. Hook III An Ounce of Prevention Ann Intern Med, November 15, 2005; 143(10): 751 - 752. [Full Text] [PDF]
|
|