Rickettsiae and Other Related Intracellular Bacteria

Treatable rickettsial infections, including life-threatening Rocky Mountain spotted fever, boutonneuse fever, epidemic typhus, murine typhus, scrub typhus, human monocytotropic ehrlichiosis, and human granulocytotropic anaplasmosis, are seldom diagnosed serologically during the acute stage of illness owing to absence of an early antibody response. Immunohistochemistry and molecular diagnostics are effective in diagnosing rickettsioses and ehrlichioses, respectively. Q fever endocarditis is a chronic infection that usually is diagnosed by detecting a high titer (≥1:800 by immunofluorescent antibody assay) of antibodies against Coxiella burnetii phase I antigen. The clinicoepidemiologic diagnosis of cat scratch disease can be confirmed serologically by antibodies to Bartonella henselae or by polymerase chain reaction testing of lymph node aspirates.