A 28-year-old man is seen in clinic with a nonpurulent urethral discharge. He has had condomless sex with two female partners in the last 3 months. A nucleic acid amplification test (NAAT) is ordered for Chlamydia trachomatis and Neisseria gonorrhoeae on a first-catch urine. He is empirically treated with oral doxycycline 100 mg twice daily for 7 days. His urethral symptoms do not improve, and he is seen again 2 weeks later. The tests for chlamydia and gonorrhea at the initial evaluation were negative. Additional testing was performed at this visit, and a urine NAAT was positive for Trichomonas vaginalis.