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Biomarker Validation of Recent Unprotected Sexual Intercourse in a Prospective Study of Young Women Engaged in Sex Work in Phnom Penh, Cambodia

Evans, Jennifer L. MS*; Couture, Marie-Claude PhD*; Stein, Ellen S. MPH*; Sansothy, Neth MD; Maher, Lisa PhD; Page, Kimberly PhD, MPH*Young Women’s Health Study Collaborative

Sexually Transmitted Diseases: June 2013 - Volume 40 - Issue 6 - p 462–468
doi: 10.1097/OLQ.0b013e318286db8a
Original Study

Background Accurate measurement of unprotected sex is essential in HIV prevention research. Since 2001, the 100% Condom Use Program targeting female sex workers (FSWs) has been a central element of the Cambodian National HIV/AIDS Strategy. We sought to assess the validity of self-reported condom use using the rapid prostate-specific antigen (PSA) test among Cambodian FSWs.

Methods From 2009 to 2010, we enrolled 183 FSWs in Phnom Penh in a prospective study of HIV risk behavior. Prostate-specific antigen test results from the OneStep ABAcard were compared with self-reported condom use in the past 48 hours at quarterly follow-up visits.

Results Among women positive for seminal fluid at the first follow-up visit, 42% reported only protected sex or no sex in the detection period. Discordant results were more likely among brothel and street-based FSW versus entertainment (56% vs. 17%), recent (last 3 months) amphetamine-type stimulant (ATS) users (53% vs. 20%), and those with 5 or more partners in the past month (58% vs. 13%). In multivariable regression models, positive PSA results were associated with recent ATS use (adjusted risk ratio [ARR], 1.5; 95% confidence interval [CI], 1.1–2.2), having a nonpaying last sex partner (ARR, 1.7; CI, 1.2–2.5), and sex work venue (ARR, 3.0; CI, 1.4–6.5). Correspondingly, women with a nonpaying last sex partner were more likely to report unprotected sex (ARR, 1.5; CI, 1.1–2.2), but no associations were found with sex work venue or ATS use.

Conclusions Results confirm the questionable validity of self-reported condom use among FSW. The PSA biomarker assay is an important monitoring tool in HIV/sexually transmitted infection research including prevention trials.

A study of female sex workers in Phnom Penh, Cambodia, found self-reported condom use to be of questionable validity, particularly among amphetamine-type stimulant users and those with multiple partners.

From the *Department of Epidemiology and Biostatistics, University of California, San Francisco, San Francisco, CA; †National Institute for HIV, AIDS, Dermatology and STDs, Phnom Penh, Cambodia; and ‡The Kirby Institute, University of New South Wales, Sydney, Australia

The following are Young Women’s Health Study Collaborative members: John Kaldor, Serey Phal, Lisa Maher, Tooru Nemoto, Kimberly Page, Joel Palefsky, Saphonn Vonthanak, and Mean Chhi Vun.

The authors acknowledge the study participants, who contributed their time and effort to make this study a success. They also recognize the contributions made by the clinical and administrative staff at Cambodian Women’s Development Agency and the research team at the National Center for HIV/AIDS and Dermatology in Phnom Penh, Cambodia.

Supported by the National Institutes of Health (Grants U01-AI0154241, R21-DA025441, and R01-NR010995).

Conflict of interest: None declared.

The contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health.

Correspondence: Jennifer L. Evans, MS, Prevention and Public Health Group, University of California San Francisco, 50 Beale St Suite 1200, San Francisco, CA 94105. E-mail:

Received for publication June 19, 2012, and accepted January 8, 2013.

© Copyright 2013 American Sexually Transmitted Diseases Association