A 32-year-old man is evaluated for a 3-day history of abdominal cramping and non-bloody diarrhea. He denies fever, chills, urethral symptoms, anorectal pain, anal discharge, and other systemic symptoms. He engages in receptive anal intercourse as well as anilingus (oral-anal contact) and reports having four male sex partners in the past 6 months. He rarely uses condoms. He tested negative for HIV approximately 4 months prior. In further discussion, he reports that two of his sex partners have recently had similar symptoms.