title: Biomarker validation of self-reported sex among middle-aged female sex workers in China.
abstract: The objective of this study was to examine information bias arising from self-reported sexual activity and its association with syphilitic infections among female sex workers (FSWs) aged 35 years and older in China.
  
  
  
  A questionnaire was administered to 1245 middle-aged FSWs. Respondents self-reported sexual intercourse in the past 48 hours. The prostate-specific antigen test was used to verify self-reported sexual activity. FSWs were considered discordant if they indicated no sexual intercourse in the past 48 hours on the questionnaire and had a positive prostate-specific antigen test. Logistic regression was used to assess the associations between discordance and syphilis.
  
  
  
  Three hundred twenty FSWs self-reported no engagement in sexual intercourse in the past 48 hours. One-fourth of respondents (25%) were discordant. Twenty-two percent and 35.8% of discordant FSWs tested positive for active and prevalent syphilis, respectively. After adjusting for confounders, discordant FSWs had 3.8 times the odds of active syphilis (95% confidence interval: 1.52-9.30) and 2.6 times the odds of prevalent syphilis (95% confidence interval: 1.37-5.02), compared with concordant FSWs.
  
  
  
  FSWs who had active or prevalent syphilis were more likely to be discordant. Data collected via self-reported questionnaire may not be a valid tool to assess sexual behavior.
authors.affiliation: School of Public Health, University of Maryland, College Park. Electronic address: jlguida@umd.edu.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Guida
authors.affiliation: School of Public Health, University of Maryland, College Park.
authors.forename: Ami
authors.initials: A
authors.lastname: Fukunaga
authors.affiliation: School of Public Health, University of Maryland, College Park.
authors.forename: Hongjie
authors.initials: H
authors.lastname: Liu
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood*; D002681:China / Q000453:epidemiology; D017280:Condoms / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008875:Middle Aged; D015995:Prevalence; D017430:Prostate-Specific Antigen / Q000097:blood*; D012309:Risk-Taking; D057566:Self Report; D060386:Sex Workers / Q000706:statistics & numerical data*; D012725:Sexual Behavior / Q000706:statistics & numerical data*; D013587:Syphilis / Q000453:epidemiology; D047568:Unsafe Sex / Q000706:statistics & numerical data*
chemical_list: D015415:Biomarkers; D017430:Prostate-Specific Antigen
keywords: HIV; STI; Self-reported measures; Sex worker; Validity