Validity of self-reported 'safe sex' among female sex workers in Mombasa, Kenya - PSA analysis

Maria F. Gallo, F. M. Behets, M. J. Steiner, S. C. Thomsen, W. Ombidi, S. Luchters, C. Toroitich-Ruto, M. M. Hobbs

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We assessed the validity of self-reported sex and condom use by comparing self-reports with prostate-specific antigen (PSA) detection in a prospective study of 210 female sex workers in Mombasa, Kenya. Participants were interviewed on recent sexual behaviours at baseline and 12-month follow-up visits. At both visits, a trained nurse instructed participants to self-swab to collect vaginal fluid specimens, which were tested for PSA using enzyme-linked immunosorbent assay (ELISA). Eleven percent of samples (n = 329) from women reporting no unprotected sex for the prior 48 hours tested positive for PSA. The proportions of women with this type of discordant self-reported and biological data did not differ between the enrolment and 12-month visit (odds ratio [OR] 1.1; 95% confidence interval [CI] 0.99, 1.2). The study found evidence that participants failed to report recent unprotected sex. Furthermore, because PSA begins to clear immediately after exposure, our measures of misreported semen exposure likely are underestimations.

Original languageEnglish
Pages (from-to)33-38
Number of pages6
JournalInternational Journal of STD & AIDS
Issue number1
Publication statusPublished - 1 Jan 2007
Externally publishedYes


  • Behavioural research
  • Biological markers
  • Condoms
  • Prostate-specific antigen

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