Severe respiratory diphtheria-like illness caused by toxigenic Corynebacterium ulcerans

Helleren R, Fløystad HK, Tellefsen OA, Boskovic M, Skraastad T, Mengshoel AT, Alfsnes K, Skogen V. Severe respiratory diphtheria-like illness caused by toxigenic Corynebacterium ulcerans. Emerg Infect Dis. 2026;32(2):285-287.

Summary

This research letter describes a severe diphtheria‑like respiratory illness caused by toxigenic Corynebacterium ulcerans bacteremia in a 74‑year‑old immunocompromised man in Norway. The patient presented with acute respiratory distress following a prodrome of sore throat and cold‑like symptoms; initial examination showed wheezing and hypoxemia but no obvious pharyngeal membranes. Imaging suggested pneumonia, and broad‑spectrum antibiotics with steroids and bronchodilators were started. Blood cultures flagged gram‑positive rods, and MALDI‑TOF mass spectrometry identifiedC. ulcerans, prompting focused evaluation. Reference laboratory work confirmed species identification, presence of the tox gene by PCR, and in vitro toxin production by a modified Elek test; whole‑genome sequencing classified the isolate as a previously unreported sequence type. Clinical deterioration with respiratory failure, ventricular tachycardia, and the later development of sensorimotor polyneuropathy were consistent with systemic diphtheria toxin effects on myocardium and peripheral nerves. Bronchoscopy revealed and removed extensive pseudomembranes in the lower airways. The patient received diphtheria antitoxin and 14 days of targeted antibiotics, with subsequent microbiologic clearance and clinical recovery, though with residual neuropathy at two‑month follow‑up. Despite having pre‑existing protective antitoxin titers that rose further during illness, the patient developed fulminant disease, emphasizing that high antibody levels may not fully prevent severe toxin‑mediated complications in heavily immunocompromised hosts. The authors highlight the likely zoonotic origin—possibly from a household dog, within a setting lacking systematic animal surveillance, and underline the need for clinical awareness and appropriate laboratory methods to detect toxigenic Corynebacterium species in low‑incidence countries.

Comment

This case underscores that rapid clinical recognition of diphtheria‑like symptoms, combined with high‑quality microbiology (including blood cultures, toxin testing, and sequencing), is crucial for guiding antitoxin therapy and infection control. Diphtheria and diphtheria‑like disease remain non‑eradicable because animal reservoirs, environmental persistence, and incomplete population immunity continue to allow sporadic, life‑threatening cases even in highly vaccinated settings.

By Prof. Joe Schmitt — Editor-in-Chief, Global Health Press