Bartonella quintana endocarditis with positive serology for Coxiella burnetii.

Both Bartonella quintana and Coxiella burnetii are known to cause of blood culture negative endocarditis. In such case, the diagnosis is usually established by serology. A case of Bartonella quintana endocarditis is described where the serology was falsely positive for Coxiella burnetii. This case demonstrates the difficulty in distinguishing these two etiologic agents by routine serologic testing.