A female client reports green-yellow vaginal discharge, vaginal itching, and foul-smelling genitals.She has been sexually active for six months in a monogamous relationship with her boyfriend.Both were tested for sexually transmitted diseases when she received a hormonal implant five months ago.The couple broke up a month ago, and since then, she has had unprotected sex with two partners.The client's symptoms are most consistent with which of the following conditions?