Cluster of Nontoxigenic Corynebacterium diphtheriae Infective Endocarditis and Rising Background C. diphtheriae Cases-Seattle, Washington, 2020-2023.

Background: Nontoxigenic Corynebacterium diphtheriae, often associated with wounds, can rarely cause infective endocarditis (IE). Five patients with C. diphtheriae IE were identified within 12 months at a Seattle-based hospital system. We reviewed prior C. diphtheriae-positive cultures to determine if detections had increased over time and evaluated epidemiologic trends.
Methods: We conducted a formal electronic health record search to identify all patients aged ≥18 years with C. diphtheriae detected in a clinical specimen (ie, wound, blood, sputum) between 1 September 2020 and 1 April 2023. We collected patient demographics, housing status, comorbidities, substance-use history, and level of medical care required at detection. We extracted laboratory data on susceptibilities of C. diphtheriae isolates and on other pathogens detected at the time of C. diphtheriae identification.
Results: Between 1 September 2020 and 1 April 2023, 44 patients (median age, 44 years) had a C. diphtheriae-positive clinical culture, with most detections occurring after March 2022. Patients were predominantly male (75%), White (66%), unstably housed (77%), and had a lifetime history of injecting drugs (75%). Most C. diphtheriae-positive cultures were polymicrobial, including wound cultures from 36 (82%) patients and blood cultures from 6 (14%) patients, not mutually exclusive. Thirty-four patients (77%), including all 5 patients with C. diphtheriae IE, required hospital admission for C. diphtheriae or a related condition. Of the 5 patients with IE, 3 died of IE and 1 from COVID-19.
Conclusions: Findings suggest a high-morbidity outbreak disproportionately affecting patients who use substances and are unstably housed.
Competing Interests: Potential conflicts of interest. E. N. K. and E. J. C. received Infectious Diseases Society of America (IDSA) travel grants to attend ID Week. T. F. received a travel grant to attend the Conference on Retroviruses and Opportunistic Infections (CROI). H. N. K. is funded by the National Institute for Allergy and Infectious Diseases and Gilead, with funds paid directly to the institution, unrelated to this work. P. S. P. and E. J. C. received honoraria for teaching CME courses through Providence Health System, unrelated to this work. All other authors report no potential conflicts. All authors have completed the ICMJE conflict of interest forms. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
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