Acute Pericarditis Viral and idiopathic causes account for 80-90% of cases of acute pericarditis (AP) in immunocompetent patients from developed countries. Therefore empiric treatment and extensive search for an underlying cause is unnecessary in the majority of cases we see. However, the etiology of AP in developing countries is very different, with TB-related AP predominating. 70-80% of cases from Sub-Saharan Africa and more than 90% of HIV-related cases of AP are tuberculous. Therefore, in the U.S. tuberculous pericarditis should be strongly considered among immigrants/visitors from developing countries and among patients with HIV.