Clinical features of experimental human infection with haemophilus ducreyi

Haemophilus ducreyi is the etiologic agent of chancroid, which facilitates the transmission of HIV. The purpose of this study was to standardize the human challenge model of H. ducreyi infection with a human passaged variant of strain 35000 (35000HP). Twenty healthy adult volunteers were challenged with two doses (∼30 cfu) of live and one dose of heat-killed 35000HP inoculated into the skin. Subjects were infected for up to 2 weeks or until they developed a painful or pruritic pustular lesion. Surface cultures were obtained daily. Patients were biopsied and treated with oral ciprofloxacin. Papules developed at 95% (95% CI; 83.1 to 99.4%) of sites infected with live bacteria. Papules resolved spontaneously at 26% of sites. Pustules developed within 2 to 5 days at 70% (95% CI; 47.1 to 86.6%)of sites. In some volunteers, one site resolved while a second site became a pustule, suggesting that local factors play a role in lesion outcome. The recovery rate of H. ducreyi from surface cultures ranged from 13% to 41%. H. ducreyi was recovered from 12 of 15 pustules (80%) and from 1 of 7 papules (14%). The clinical course of experimental infection resembled the initial stages of human chancroid and is biologically relevant, safe, well tolerated and reproducible.