Chancroid is a sexually transmitted disease (STD) caused by the organism Haemophilus ducreyi. It is characterized by painful genital ulcers and tender inguinal adenopathy that may suppurate. Also known as “soft chancre,” chancroid is 1 of the 3 major causes of genital ulcer disease (GUD) among young sexually active patients in the United States; the other major causes are genital herpes and syphilis.
PATHOGENESIS AND EPIDEMIOLOGY
H ducreyi invades the skin after disruption of the epithelial surface following trauma. An infecting dose of as few as 30 colony-forming units is thought to be able to produce papules in the skin. Once a papule appears, the disease progresses to a pustule in the majority of patients, although as many as 30% of those infected may have spontaneous resolution of their pustule. Although the pathogenesis of this organism has been well studied, additional studies are required to clearly define the virulence factors.
The prevalence of chancroid is low in the United States. The reason for this low prevalence may be due to underdiagnosis. Most clinicians do not have clinical experience with chancroid and thus do not consider it in the differential diagnosis. Additionally, most laboratories do not have the capability of isolating H ducreyi. Chancroid cases peaked to a high of 5001 in the United States in 1988 and have steadily declined, with the lowest number (6 cases) in 2014, reported by the states of California, Texas, and Massachusetts. In comparison, there were 19,999 cases of primary and secondary syphilis reported in 2014.
Some data suggest that the disappearance of chancroid in the United States may be due to lack of testing and underreporting. In a survey of 405 STD clinics in 1996, only 32 (8%) tested patients for chancroid. Surveys in California from 1996 to 2003 found that less than 300 tests for chancroid were done, accounting for less than 0.1% of all tests done for STDs. However, in genital ulcer studies during the late 1990s where testing for H ducreyi was done, chancroid was frequently found. In a study in Brooklyn, New York, H ducreyi was identified in 27 (42%) of 65 cases in which a microbiologic diagnosis was established. Coinfection with syphilis was common. In New Orleans, Louisiana, similar findings were reported in 299 men with non-syphilitic genital ulcers; 39% had H ducreyi, 19% had herpes simplex virus (HSV), and the culture was negative in 41%. Using the sensitive polymerase chain reaction (PCR), it appears that chancroid may be even more common than previously thought. In a PCR study in Jackson, Mississippi, in 1995, 59% of genital ulcer cases were due to H ducreyi. In 1998, cases of chancroid identified by PCR in Memphis and Chicago accounted for 12% to 20% of genital ulcers. In 10 patients with chancroid in Memphis, none were identified clinically. Thus, the burden of chancroid in the United States is unknown.