title: Case-crossover analysis of condom use and herpes simplex virus type 2 acquisition.
abstract: BACKGROUND
  Although growing evidence suggests that condoms offer moderate protection against herpes simplex virus type 2 (HSV-2), inability to control for unknown or unmeasured confounders associated with sexual activity may reduce the accuracy of the estimates. The case-crossover design offers increased control of individual-level confounders, and was thus used with the aim of producing a more accurate estimate of the effect of condom use on HSV-2 acquisition.
  
  
  METHODS
  Data were pooled from 6 prospective studies that measured HSV-2 status at enrollment and over follow-up, and included periodic self-reported condom use and sexual activity. Sexual activity contemporaneous with acquisition was assigned to a case period; earlier sexual activity was assigned to a control period. Conditional logistic regression was used to assess differences in behavior during the case and control periods.
  
  
  RESULTS
  One hundred ninety-one eligible participants acquired HSV-2 during follow-up. This approach detected a 3.6% increase in the odds of HSV-2 acquisition with each unprotected act (odds ratio = 1.036; 95% confidence interval: 1.021-1.052), but no increase in the odds of acquisition associated with protected acts (odds ratio = 1.008; 95% confidence interval: 0.987-1.030).
  
  
  CONCLUSIONS
  This analysis suggests that condoms offer significant protection against HSV-2 transmission.
authors.affiliation: Departments of Epidemiology, University of Washington, Seattle, WA, USA.
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Stanaway
authors.forename: Anna
authors.initials: A
authors.lastname: Wald
authors.forename: Emily T
authors.initials: ET
authors.lastname: Martin
authors.forename: Sami L
authors.initials: SL
authors.lastname: Gottlieb
authors.forename: Amalia S
authors.initials: AS
authors.lastname: Magaret
mesh_terms: D000293:Adolescent; D000328:Adult; D017280:Condoms / Q000706:statistics & numerical data*; D018592:Cross-Over Studies; D005260:Female; D005500:Follow-Up Studies; D006558:Herpes Genitalis / Q000453:epidemiology / Q000517:prevention & control*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012307:Risk Factors; D012725:Sexual Behavior / Q000706:statistics & numerical data*; D055815:Young Adult