A 30-year-old woman from Kenya is referred to a sexual health clinic for evaluation of a painful vulvar ulcer. The ulcer is roughly 1 cm in diameter and has an erythematous base with ragged borders. Examination also reveals tender right-sided inguinal adenopathy. She first noticed the lesion 4 days ago, and her most recent sexual activity occurred just prior to leaving Kenya 2 weeks ago. She denies fever and feels well, except for pain at the ulcer site. Empiric treatment is given for syphilis and herpes simplex virus (HSV). She returns 1 week later with no improvement, and test results for syphilis, HSV, and HIV are negative. A diagnosis of chancroid is considered at this point.