Chancroid (also known as soft chancre and ulcus molle ) is a bacterial sexually transmitted infection characterized by painful sores on the genitalia. Chancroid is known to spread from one individual to another solely through sexual contact.
These are only local and no systemic manifestations are present. The ulcer characteristically:
- Ranges in size dramatically from 3 to 50 mm (1/8 inch to two inches) across
- Is painful
- Has sharply defined, undermined borders
- Has irregular or ragged borders
- Has a base that is covered with a gray or yellowish-gray material
- Has a base that bleeds easily if traumatized or scraped
- painful lymphadenopathy occurs in 30 to 60% of patients.
- dysuria (pain with urination) and dyspareunia (pain with intercourse) in females
About half of infected men have only a single ulcer. Women frequently have four or more ulcers, with fewer symptoms.
The initial ulcer may be mistaken as a "hard" chancre, the typical sore of primary syphilis, as opposed to the "soft chancre" of chancroid.
Approximately one-third of the infected individuals will develop enlargements of the inguinal lymph nodes, the nodes located in the fold between the leg and the lower abdomen.
Half of those who develop swelling of the inguinal lymph nodes will progress to a point where the nodes rupture through the skin, producing draining abscesses. The swollen lymph nodes and abscesses are often referred to as buboes.
Chancroid is a bacterial infection caused by the fastidious Gram-negative streptobacillus Haemophilus ducreyi. It is a disease found primarily indeveloping countries, most prevalent in low socioeconomic groups, associated with commercial sex workers. In the United States socioeconomic status has not been found to be a factor in the spread of sexually transmitted diseases. 
Chancroid, caused by H. ducreyi has infrequently been associated with cases of Genital Ulcer Disease in the US, but has been isolated in up to 10% of genital ulcers diagnosed from STD clinics in Memphis and Chicago.
Infection levels are very low in the Western world, typically around one case per two million of the population (Canada, France, Australia, UK and US). Most individuals diagnosed with chancroid have visited countries or areas where the disease is known to occur frequently, although outbreaks have been observed in association with crack cocaine use and prostitution.
Chancroid is a risk factor for contracting HIV, due to their ecological association or shared risk of exposure, and biologically facilitated transmission of one infection by the other.
Chancroid spreads in populations with high sexual activity, such as prostitutes. Use of condom, prophylaxis by azithromycin, syndromic management of genital ulcers, treating patients with reactive syphilis serology are some of the strategies successfully tried in Thailand.
From bubo pus or ulcer secretions, H. ducreyi can be identified. PCR-based identification of organisms is available. Simple, rapid, sensitive and inexpensive antigen detection methods for H. ducreyi identification are also popular. Serologic detection of H. ducreyi is and uses outer membrane protein and lipooligosaccharide.
Prognosis is excellent with proper treatment. Treating sexual contacts of affected individual helps break cycle of infection.
The CDC recommendation for chancroid is a single oral dose (1 gram) of azithromycin, or a single IM dose of ceftriaxone, or oral erythromycin for seven days.
Abscesses are drained.
H.ducreyi is resistant to sulfonamides, tetracyclines, penicillins, chloramphenicol, ciprofloxacin, ofloxacin, trimethoprim and aminoglycosides. Recently, several erythromycin resistant isolates have been reported.
Treatment failure is possible with HIV co-infection and extended therapy is sometimes required.