<prompt> Chancroid is caused by ?H. DucreiN. GonnorrheaT. PallidumH. Influenza  <response>: ANSWER: A H. Ducrei REF: Roxburghs Common Skin Diseases p. 102 Repeat in June 2010 See APPENDIX-47 below for list of STDs CHANCROID SOFT SORE This venereal infection is caused by the Gram-negative bacillus Haemophilus ducreyi. One to 5 days post-infection, a soft sloughy ulcer appears on the penis or vulva. The treatment of choice is erythromycin 500 mg 6-hourly for 14 days. 