Use of dot-immunobinding and immunofluorescence assays to investigate clinically suspected cases of chancroid.

In 1984 and 1985, outbreaks of genital ulcers occurred in Florida and New York. Initial investigations for syphilis, herpes simplex, Chlamydia trachomatis, and Haemophilus ducreyi did not implicate any of these organisms as etiologic agents. From the results of dot-immunobinding assays, we found that sera from the patients had higher levels of IgM (30 [47.6%] of 63 patients) and IgG (22 [34.9%] of 63 patients) reactivities with an outer-membrane preparation from H. ducreyi strain CIP542 than with outer-membrane preparations from Haemophilus influenzae ATCC 10211 or Haemophilus parainfluenzae ATCC 7901. In contrast, sera from 35 patients in the control group did not react with any of the outer-membrane preparations (P less than .01 for both IgM and and IgG reactivity), nor did sera from eight individuals with disease caused by H. influenzae (P = .051 for IgM reactivity, P = .02 for IgG reactivity). Indirect immunofluorescence assay using a monoclonal antibody reactive with outer-membrane preparations from H. ducreyi strain CIP542 stained organisms in smears of lesion material from genital ulcers from three of six patients. These results suggested that the cause of both outbreaks of genital ulcers was H. ducreyi which was subsequently isolated in both geographic areas.