Legionnaires' disease. Pathological and historical aspects of a 'new' disease.

Autopsy tissues and protocols from 26 epidemiologically defined fatal cases of Legionnaires' disease occurring during the 1976 Philadelphia outbreak were reviewed. Consistent pathologic features were limited to the lung, where an acute pneumonia characterized by intra-alveolar exudation of neutrophils, macrophages, and fibrin was observed. An etiologic agent common to most of the victims of Legionnaires' disease was identified within the pneumonic process by application of the Dieterle silver impregnation stain. In some cases, other pulmonary histologic findings were noted, chiefly acute diffuse alveolar damage. However, the importance of acute diffuse alveolar damage is not understood.