H. ducreyi is the etiologic agent of chancroid, an STI characterized by genital ulceration and inguinal adenitis. In addition to being a cause of morbidity in itself, chancroid increases the efficiency of transmission of and degree of susceptibility to HIV infection. See Table 83-1 for clinical details. Culture of H. ducreyi from the lesion confirms the diagnosis; PCR is starting to become available. In the setting of a compatible clinical presentation (including one or more painful genital ulcers) and negative tests for syphilis and HSV infection, a probable diagnosis of chancroid can be made.