Standardization of the experimental model of Haemophilus ducreyi infection in human subjects

Human volunteers were challenged with Haemophilus ducreyi. Twenty subjects were inoculated with 2 doses (approximately 30 cfu) of live and 1 dose of heat-killed bacteria at 3 sites on the arm. Eight subjects were assigned to biopsy 1 or 4 days after inoculation, and 12 were biopsied after they developed a painful pustular lesion or were followed until disease resolved. Papules developed at 95% of 40 sites infected with live bacteria (95% confidence interval [CI], 83. 1%-99.4%). In 24 sites followed to end point, 27% of the papules resolved, 69% (95% CI, 47.1%-86.6%) evolved into pustules, and 4% remained at the papular stage. Recovery rates of H. ducreyi from surface cultures ranged from 13% to 41%. H. ducreyi was recovered from biopsies of 12 of 15 pustules and 1 of 7 papules, suggesting that H. ducreyi replicates between the papular and pustular stages of disease.