Pediatric Infective Endocarditis Due to Streptococcus mitis: A Case Report.

Infective endocarditis in pediatrics is a rare but serious condition, even in immunocompetent children without congenital heart disease. Streptococcus mitis, a commensal inhabitant of the oral cavity, has emerged as a relevant etiological agent capable of causing invasive infections due to its strong endothelial adherence and biofilm formation. Accurate microbiological identification requires advanced tools such as matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, given its genetic similarity to Streptococcus pneumoniae. This case report presents a 12-year-old female patient with a history of a ventricular septal defect and persistent respiratory symptoms. After multiple ineffective treatments, an echocardiogram revealed cardiac vegetations consistent with IE. Blood cultures confirmed Streptococcus mitis infection, prompting targeted antibiotic therapy. The patient underwent surgical resection of pulmonary valve vegetations and closure of the ventricular septal defect. Chest computed tomography revealed an infectious pneumatocele, suggesting septic embolization. This case highlights the potential for pulmonary involvement secondary to right-sided endocarditis, even in the absence of traditional risk factors. Vegetations larger than 10 mm were associated with lower response to medical therapy and a higher risk of embolization, supporting the need for surgical intervention. Streptococcus mitis should be considered a potential pathogen in pediatric infective endocarditis, even in patients without comorbidities. Persistent fever, positive blood cultures, and atypical pulmonary findings warrant prompt echocardiographic evaluation. Accurate diagnosis and early treatment are essential to reduce complications and improve clinical outcomes.