Pulmonary pathology of Rocky Mountain spotted fever (RMSF) in children.

Despite infrequent respiratory symptoms, histopathologic changes were identified in the lungs of 15 of 16 children dying of Rocky Mountain spotted fever (RMSF). Gross examination demonstrated increased lung weight, edema, congestion, focal hemorrhage, and bronchopneumonia in a few cases. Paraffin sections were stained with hematoxylin and eosin and phosphotungstic acid-hematoxylin, and available blocks were examined by direct immunofluoresence for Rickettsia rickettsii. Cases and controls matched for age and sex were randomized and examined blindly for pathologic changes. In addition, morphometric measurements of mean alveolar septal thickness were made in each case. The histopathologic findings include (1) diffuse interstitial mononuclear (lymphocyte and macrophage) inflammatory infiltrate in 15/16 cases of RMSF (5/10 controls), (2) pulmonary edema and intraalveolar hemorrhage in 11/16 cases of RMSF (2/10 controls), and (3) vasculitis of small pulmonary venules and arterioles in 5/16 RMSF cases (0/10 controls). Rickettsia rickettsii were identified in 4/8 RMSF cases by direct fluorescent antibody technique. Although pulmonary disease is not always clinically apparent in children with RMSF, involvement of the pulmonary microcirculation is a frequent event in fatal cases and may contribute to the development of non-cardiogenic pulmonary edema.