Investigations of 2 Cases of Diphtheria-Like Illness Due to Toxigenic Corynebacterium ulcerans

Background. We present 2 case reports in the United States and investigations of diphtheria-like illness caused by toxigenic Corynebacterium ulcerans. A fatal case occurred in a 75-year-old male Washington resident who was treated with clindamycin but did not receive equine diphtheria antitoxin. A second, nonfatal case occurred in a 66-year-old female Tennessee resident who received erythromycin and diphtheria antitoxin. Methods. Both case patients and close human and animal contacts were investigated by their respective state health departments. Results. C. ulcerans isolated from the patient who died was resistant to erythromycin and clindamycin. For both isolates, conventional polymerase chain reaction results were positive for A and B subunits of diphtheria toxin gene tox, and modified Elek tests confirmed toxin production. The source of infection remained undetermined for both cases. Neither patient was up-to-date with diphtheria toxoid vaccination. Conclusion. These case reports highlight the importance of early treatment with diphtheria antitoxin, the selection of effective antimicrobial agents, and prevention through up-to-date vaccination.