Background. Trichomonas vaginalis infection is a common sexually transmitted protozoal infection and is associated with several adverse health outcomes, such as preterm birth, delivery of a low-birth weight infant, and facilitation of sexual transmission of human immunodeficiency virus. The annual incidence in the United States has been estimated to be 3-5 million cases. However, there are no data on the prevalence of trichomoniasis among all reproductive-age women. We estimated the prevalence

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... f T. vaginalis infection from a nationally representative sample of women in the United States. Methods. Women aged 14-49 years who participated in the National Health and Examination Survey cycles for 2001-2004 provided self-collected vaginal swab specimens. The vaginal fluids extracted from these swabs were evaluated for the presence of T. vaginalis using polymerase chain reaction. Results. Overall, 3754 (81%) of 4646 women provided swab specimens. The prevalence of T. vaginalis infection was 3.1% (95% confidence interval [CI], 2.3%-4.3%); for non-Hispanic white women, it was 1.3% (95% CI, 0.7%-2.3%); for Mexican American women, it was 1.8% (95% CI, 0.9%-3.7%); and for non-Hispanic black women, it was 13.3% (95% CI, 10.0%-17.7%). Factors that remained associated with increased likelihood of T. vaginalis infection in multivariable analyses included non-Hispanic black race/ethnicity, being born in the United States, a greater number of lifetime sex partners, increasing age, lower educational level, poverty, and douching. Conclusions. The prevalence of T. vaginalis infection among women in the United States was 3.1%. A significant racial disparity exists; the prevalence among non-Hispanic black women was 10.3 times higher than that among non-Hispanic white and Mexican American women. Optimal prevention and control strategies for T. vaginalis infection should be explored as a means of closing the racial disparity gaps and decreasing adverse health outcomes due to T. vaginalis infection. Trichomonas vaginalis infection is a common sexually