This patient with fever and chest pain has a turbid pericardial effusion with a high number of neutrophils, indicating purulent pericarditis.  Most cases are caused by bacteria or fungi and develop due to:

• Hematologic spread from a distant infection
• Direct extension from an adjacent pneumonia or cardiac infection (eg, endocarditis, perivalvular abscess)
• Complication of penetrating chest injury or cardiothoracic surgery

Staphylococcus aureus, a gram-positive cocci that grows in clusters, is the most frequently isolated organism.  It is particularly likely in patients who have portals from the skin to the bloodstream (eg, tunneled dialysis catheter) or from the skin directly to the pericardium (eg, chest injury, recent cardiothoracic surgery).  Streptococcus pneumoniae is the most common organism in patients with adjacent pneumonia.

Although Candida albicans, a budding yeast that forms germ tubes, is a leading cause of fungal pericarditis, it is seen primarily in persons with significant risk factors for candidemia such as parenteral feeding, prolonged corticosteroid use, or immunosuppression due to malignancy; S aureus is far more common in patients with end-stage renal disease who have vascular catheters (Choice B).

(Choice A)  Mycobacterium tuberculosis, an acid-fast bacilli, can occasionally cause purulent pericarditis due to direct spread from the lung or a mediastinal/hilar lymph node, but S aureus is far more likely in someone with a hemodialysis catheter.

(Choice D)  Lactose-fermenting gram-negative bacilli (eg, Escherichia coli, Klebsiella pneumoniae, Enterobacter) are uncommon causes of purulent pericarditis.  Although Klebsiella pericarditis can occasionally occur due to adjacent anaerobic lung abscess, this patient with an indwelling catheter is far more likely to have S aureus infection.

(Choice E)  Borrelia burgdorferi is a motile spirochete seen with silver stain.  It can cause Lyme myopericarditis as a consequence of early disseminated disease, but most cases are mild and asymptomatic.  In addition, an effusion caused by B burgdorferi infection would be lymphocyte (not neutrophil) predominant.

(Choice F)  Although single-stranded RNA viruses such as Coxsackievirus can cause pericarditis, the pericardial fluid is usually lymphocyte (not neutrophil) predominant.

Educational objective:
Purulent pericarditis is usually caused by hematogenous dissemination from distant infection or direct extension from an adjacent infection or chest wall trauma.  Although a variety of organisms cause purulent pericarditis, Staphylococcus aureus is the most common pathogen, particularly in the setting of a portal from the skin to the bloodstream (eg, catheter) or pericardium (eg, recent chest surgery, penetrating injury).