A 22-year-old woman attends the STI clinic with a 3-day history of dysuria, urinary frequency, and mucopurulent urethral discharge. On examination, she is afebrile with no systemic signs. Gram stain of urethral smear shows gram-negative intracellular diplococci within neutrophils. She reports unprotected sexual contact 5 days ago. What is the most appropriate immediate next step in management?