A 43-year-old businessman visits his primary care physician complaining of a purulent penile discharge. He had unprotected sex with a woman he met at a conference 1 week ago. Gram stain of the discharge fails to reveal any organisms. Which of the following is the most likely cause of the discharge?

C. trachomatis is one of the leading causes of urethritis and should be suspected whenever a gonorrhea-like discharge fails to show gram-negative diplococci within neutrophilic phagocytes. It is a sexually transmitted disease that can also cause epididymitis. Bowen disease presents as a single erythematous plaque on the penis or scrotum and may evolve into invasive carcinoma. Herpes simplex virus can cause a vesicular rash on the penis. T. pallidum causes syphilis, which may present with a painless chancre on the penis.