Anaerobic pericarditis due to Clostridium ramosum: First known case report.

Anaerobic pathogens are uncommon etiologies of pericardial infections. Clostridium ramosum, an obligate anaerobic gram-positive bacillus and member of the normal gastrointestinal flora, is generally considered of low virulence but has been implicated in invasive infections in elderly or immunocompromised individuals. We report the first documented case of Clostridium ramosum pericarditis. An 85-year-old male with atrial fibrillation, hypertension, hyperlipidemia, splenomegaly with bicytopenia, and depression was found to have a moderate pericardial effusion on transthoracic echocardiography. Follow-up imaging revealed a reduced ejection fraction, progressive aortic dilation, and early tamponade physiology. Despite being asymptomatic, he underwent pericardiocentesis, which yielded 400 mL of fluid. Gram stain demonstrated gram-positive bacilli, later identified on anaerobic culture as Clostridium ramosum. Blood cultures remained negative. He was treated with intravenous ampicillin-sulbactam followed by oral metronidazole, with resolution of the effusion and no recurrence on follow-up. This case highlights that anaerobic pericarditis can occur in the absence of systemic symptoms or sepsis, particularly in elderly patients with comorbidities that predispose to bacterial translocation. Timely drainage and targeted antimicrobial therapy are essential for favorable outcomes. Importantly, routine anaerobic cultures of pericardial fluid should be considered to avoid missed diagnoses. Recognition of rare anaerobic pathogens in pericardial infections expands the understanding of their pathogenic potential and informs future diagnostic and therapeutic approaches.