C. diphtheriae native-valve endocarditis in children: An emerging pathogen?

Abstract

Background: Corynebacterium diphtheriae is a gram positive bacillus common to cause diphtheria which is now uncommon due to vaccination. Occurrence of systemic diseases are very rare and few cases of endocarditis have been documented in literature. We report 3 cases of native-valve endocarditis caused by C. diphtheriae in children during 2018/2019. Case Description: Case 1 A 5-y-old girl who underwent cardiac surgery 2 y ago, presented with high fever for 3 d. Echocardiogram showed a residual VSD with a large vegetation in the right ventricular outflow tract. All 3 blood cultures grew Corynebacterium diphtheriae. Vegetation tissues did not yield any growth. She was treated successfully with uneventful recovery. Case 2 An 8 y old boy presented with a 2 m history of low-grade intermittent fever suspected of endocarditis showed myxomatous mitral valve with mild mitral regurgitation. One blood culture was taken and was positive for Corynebacterium diphtheriae. Case 3 A previously healthy 3 y old girl presented with low-grade intermittent fever for 2 w. The Echocardiogram showed a grade IV mitral regurgitation and a large vegetation [9 x 19 mm]. All 3 blood cultures grew Corynebacterium diphtheriae. Patient succumbed after surgery. The isolates were identified and antibiotic susceptibility was performed at the Reference Laboratory, Medical Research Institute by BD® Phoenix automated system. Characteristic slate gray colonies were grown on Blood Tellurite medium, positive for catalase and nitrate and negative for urease activity. Qiagen® Realtime PCR assay for Corynebacterium diphtheriae DNA was performed in isolates 2 and 3. Toxigenic studies were not performed. The isolate in case 1 was resistant to benzyl penicillin, erythromycin, cotrimoxazole, vancomycin and susceptible to linezolid. Other isolates were susceptible to all the above antibiotics. Discussion: Corynebacterium diphtheriae requires high degree of suspicion as it can be misjudged as a skin commensal in a busy hospital laboratory. In Sri Lanka, one case of native-valve endocarditis caused by Corynebacterium diphtheriae in a child has been reported previously. Conclusion: This case series highlights the importance of awareness in rare pathogens as the causative agents in common diseases and the role of microbiology laboratories in identifying these pathogens.