A non-toxigenic Corynebacterium diphtheriae biovar Belfanti isolated from a patient with rheumatoid arthritis in China: Insights from a comprehensive genome-based analysis

Rationale:Diphtheria is caused by infection with Corynebacterium diphtheriae and is typically associated with upper respiratory tract involvement, which can manifest with high invasiveness. However, in recent years, non-toxigenic C diphtheriae strains have increasingly emerged as major pathogens responsible for invasive diseases. The uniqueness of this case lies in the challenges of culturing and identifying the bacterial strain, its atypical upper respiratory tract manifestations (which are easily overlooked clinically), and its potential for covert transmission, all of which warrant heightened clinical attention. Patient concerns:A 71-year-old female patient with rheumatoid arthritis presented to the respiratory department of cough with shortness of breath for >2 months. Diagnoses:Pulmonary infections caused by Proteus vulgaris and C diphtheriae biovar Belfanti, and pulmonary interstitial fibrosis. Interventions:The patient received intravenous infusion of cefoperazone sodium and sulbactam sodium. Concurrently, doxofylline was prescribed. The patient continued to receive aerosol inhalation of Budesonide Suspension for Inhalation and levosalbutamol hydrochloride. Outcomes:The patient had improved chest tightness and shortness of breath, no other special discomfort, and stable vital signs after physical examination. Lessons:C diphtheriae biovar Belfanti strain was isolated. The strain can't decompose nitrate, no virulence gene and drug-resistance gene, but it has strong transposing ability and infection ability, and has the possibility of transforming into a pathogenic strain, which needs to be concerned.