Experimental infection of human volunteers with Haemophilus ducreyi does not confer protection against subsequent challenge

Two groups of human volunteers were inoculated with 2 doses of live Haemoph ilus ducreyi 35000HP. The reinfection group consisted of 7 subjects who pre viously had participated in experimental infection with 35000HP to the pust ular stage of disease. The control group consisted of 7 naive subjects. Pap ules developed at 92.8% (95% confidence interval [CI], 66.1%-99.8%) of site s inoculated with live bacteria, in the reinfection group, and at 85.7% (95 % CI, 57.2%-98.2%) of sites in the control group. Sixty-nine percent (95% C I, 36.8%-90.9%) of papules evolved into pustules in the reinfection group, compared with 41% (95% CI, 15.2%-72.3%) in the control group. The recovery rates of H. ducreyi from surface cultures and the histopathology of biopsie s obtained from both groups were similar. Thus, experimental infection to t he pustular stage of disease does not provide protective immunity against s ubsequent challenge.