A 23-year-old sexually active woman presents to the emergency department with a 5-day history of worsening lower abdominal pain, vaginal discharge, fever, and dyspareunia (pain during intercourse). She also reports irregular spotting between her menstrual cycles. She has had multiple sexual partners in the past year and inconsistently uses condoms. On examination, she has a low-grade fever (38.3°C/100.9°F) and mild tachycardia. Abdominal palpation reveals tenderness in the lower quadrants, and a bimanual pelvic examination demonstrates: Cervical motion tenderness Bilateral adnexal tenderness Purulent cervical discharge Transvaginal ultrasound shows thickened, fluid-filled fallopian tubes, consistent with salpingitis, but no tubo-ovarian abscess. What is the most common causative agent of this disorder?
