Immunohistologic demonstration of Coxiella burnetii in the valves of patients with Q fever endocarditis.

PURPOSE

Cardiac valves that were resected from patients with Q fever endocarditis were examined by immunohistologic methods to correlate the presence of Coxiella burnetii in the valves with the histopathologic, serologic, microbiologic, and clinical findings.

PATIENTS

Seventeen patients with serologic and microbiologic or clinical evidence of Q fever endocarditis who presented with cardiac failure secondary to valvular dysfunction and required valve replacement surgery were selected from the clinical records of the Unité des Rickettsies, Marseille, France.

METHODS

Clinical data were collected by questionnaire. Serologic characterization was performed by indirect immunofluorescent antibody testing; shell vial cultivation of C burnetii was performed from resected valves and blood when available; and pathologic and immunohistologic testing for localization of C burnetti in resected valves were performed by standard methods using both polyclonal and monoclonal C burnetti antibodies.

RESULTS

Demographic and clinical findings were typical of patients with Q fever endocarditis. Pure chronic inflammation or mixtures of acute and chronic inflammation were the most frequent inflammatory patterns present and were associated with fibrin deposition, necrosis, and fibrosis. Well-formed granulomas were not present, but the granulomatous inflammation observed in 6 of these 17 patients was associated with foreign body reactions or with valvular calcifications secondary to preexisting valvular damage and could not be directly attributed to infection. C burnetii were present nearly exclusively in macrophages in sites of inflammation and valvular injury and only in the vegetations. Immunohistologic results confirmed the valve culture results in 10 of 14 cases.

CONCLUSION

The pathologic findings in the valves of patients with Q fever endocarditis are nonspecific. The presence of empty or foamy macrophages is suggestive of infection by C burnetii; however, definitive identification rests upon the demonstration of the organism in the tissue by immunohistology. Q fever endocarditis probably results from infection of previously damaged heart valves. The finding of the absence of granulomas in these cases contrasts with the pathologic findings in patients with acute, self-limited Q fever and suggests an aberrant host immune response that permits persistence of the bacterium and chronic, prolonged valvular infection and injury. The pathologic findings and distribution of C burnetii in the damaged valve tissues explain the clinical findings of valve failure and occasional embolic episodes, as well as the frequent ability to isolate C burnetii from the peripheral blood of infected patients. Immunohistology may be a valuable diagnostic tool in places where serology and culture are not available.