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• Re “Condom effectiveness for prevention of Chlamydia trachomatis infection"
  Lee Warner
  Published on: 21 September 2005

• Published on: 21 September 2005

  Re “Condom effectiveness for prevention of Chlamydia trachomatis infection"

  • Lee Warner, Senior Health Scientist
  • Other Contributors:
    • Maurizio Macaluso, Daniel Newman, Mary Kamb, C. Kevin Malotte, Jonathan Zenilman, Harland Austin, David Kleinbaum, John Douglas

  Dear Editor

  Replicating methods and comparing results across studies are critical for the resolution of scientific controversies. In a recent report, Niccolai et al. demonstrated that condoms were effective in preventing chlamydia among STD clinic patients with known exposure to C. trachomatis.(1) We were pleased to see the authors apply the methodology that we first presented for estimating condom effectiveness...

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  Dear Editor

  Replicating methods and comparing results across studies are critical for the resolution of scientific controversies. In a recent report, Niccolai et al. demonstrated that condoms were effective in preventing chlamydia among STD clinic patients with known exposure to C. trachomatis.(1) We were pleased to see the authors apply the methodology that we first presented for estimating condom effectiveness against chlamydia and gonorrhea in 2001 (2,3) and published in the American Journal of Epidemiology last year.(4) Their findings confirm the importance of restricting the study population to persons with known STI exposure (i.e., sexual contacts of infected persons) to reduce confounding on condom effectiveness estimates against bacterial (4) and viral (5,6) infections.

  By focusing their analysis on chlamydia alone, Niccolai et al. underscore the need for disease-specific estimates of condom effectiveness. Focusing on a single disease is important because, although condoms should protect against all infections transmitted via the male urethra (including gonorrhea and chlamydia) (7), other factors, such as transmission efficiency, are disease-specific and may influence the magnitude of the protective effect. We would like to clarify for the readers, however, that the methodology we described will also allow for disease-specific estimates of protection when multiple infections are evaluated among persons with known exposure. As we noted ((4), p. 243)), the key point is that infections diagnosed among study participants must be identical to those of the participants’ infected partner. (For example, the relationship between condom use and risk for gonorrhea should be assessed only among participants exposed to gonorrhea, likewise for chlamydia). Maintaining this algorithm, we combined estimates for chlamydia and gonorrhea after observing the disease-specific point estimates (0.38 and 0.47, respectively) were neither appreciably nor significantly different from each other ((4), p. 245)). Thus, application of this methodology need not be limited to a single infection.

  Niccolai et al.’s study represents the most recent application of this methodology for estimating condom effectiveness among persons with known STI exposure, and, encouragingly, provides independent confirmation of the validity of this approach and of our earlier findings. This work adds to an increasing body of evidence (4,8,9) suggesting that studies confounded by important differences between consistent users and inconsistent or nonusers (e.g., degree of STI exposure) tend to underestimate the protective effect of condoms against bacterial STI. Studies limited to individuals with known STI exposure are likely to estimate the protective effect of condom use more accurately. Given that such studies can be conducted using secondary analyses of existing trial data (4,8) as well as routinely collected clinic data (1,9), we encourage investigators to adopt similar methodologies to reduce confounding when evaluating condom effectiveness.

  Finally, restricting the study population to sexual contacts of infected persons likely has many applications for STI research beyond assessment of condom effectiveness. This methodology for reducing confounding also may provide clearer insight into an array of potential causative and preventive factors for STI, where studies are subject to the same sources of confounding that have plagued condom effectiveness research.

  References

  1. Niccolai L., Rowhani-Rahbar A, Jenkins H, et al. Condom effectiveness for prevention of Chlamydia trachomatis infection. Sex Transm Inf 2005;81:323-5.

  2. Warner L, Newman D, Peterman T, et al. Uncontrolled confounding: a methodologic problem in evaluating condom effectiveness for prevention of sexually transmitted diseases. 2001 National HIV Prevention Conference, Atlanta, GA, August 12-15.

  3. Warner L, Newman D, Peterman T, et al. Project RESPECT Study Group. Studying condom effectiveness for sexually transmitted disease (STD) prevention: the importance of knowing partner infection status. 2002 National STD Prevention Conference, San Diego, CA, March 4-7.

  4. Warner L, Newman DR, Austin HD, et al. Condom effectiveness for reducing transmission of gonorrhea and chlamydia; the importance of assessing partner infection status. Am J Epidemiol 2004;159:242-51.

  5. Weller S, Davis K. Condom effectiveness in reducing heterosexual HIV transmission. Cochrane Database Syst Rev 2001;(3):CD003255.

  6. Wald A, Langenberg AG, Link K, et al. Effect of condoms on reducing the transmission of herpes simplex virus type 2 from men to women. JAMA 2001;285:3100-6.

  7. Centers for Disease Control and Prevention. Sexually transmitted diseases treatment guidelines 2002. MMWR 2002;51(No. RR-6).

  8. Warner L. Macaluso M, Austin HD, et al. Application of the case- crossover design to reduce unmeasured confounding in studies of condom effectiveness. Am J Epidemiol 2005;161:1-9.

  9. Shlay J, McClung MW, Patnaik JL, et al. Comparison of sexually transmitted disease prevalence by reported level of condom use among patients attending an urban sexually transmitted disease clinic. Sex Transm Dis 2004;31:154-60.

  Disclaimer: The findings and conclusions in this letter are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.

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  Conflict of Interest:
  None declared.

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