Pericarditis with effusion casued by Actinomyces israelii.

Actinomyces israelii is a rare cause of pericarditis. Infection spreads to pericardium from an intrathoracic focus. Branching gram-positive filaments are seen on microscopic examination of clinical specimens. Cultures should be performed under anaerobic conditions. Both surgical drainage and antibiotics (penicillin) are required for treatment. Nocardiosis may resemble actinomycosis in many respects.