Cluster of non-toxigenic Corynebacterium diphtheriae infective endocarditis and rising background C. diphtheriae cases—Seattle, Washington 2020-2023

Abstract BACKGROUND Non-toxigenic Corynebacterium diphtheriae (C. 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 ≥ 18 years of age with C. diphtheriae detected in a clinical specimen (i.e. wound, blood, sputum) between September 1, 2020–April 1, 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 September 1, 2020–April 1, 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 five patients with C. diphtheriae IE, required hospital admission for C. diphtheriae or a related condition. Of the five patients with IE, three died of IE and one from COVID-19. CONCLUSION Findings suggest a high-morbidity outbreak disproportionately affecting patients who use substances and are unstably housed.