Pneumonia caused by Pittsburgh pneumonia agent: radiologic manifestations.

Using an objective scoring system, chest radiographs were reviewed in 23 cases of pneumonia due to the Pittsburgh pneumonia agent (PPA, Tatlockia micdadei, Legionella micdadei), including six cases of pneumonia with simultaneous isolation of PPA and L pneumophila (Legionnaires' disease). Infiltrates were typically segmental to lobar; nodular infiltrates were noted in three cases. Spread to additional lobes after presentation occurred in four of 17 PPA infections. Pneumonia caused by both PPA and L pneumophila was unusually severe, with involvement of all lobes occurring in four of six cases, compared with one of 17 cases of PPA infection (p less than 0.02). Radiographic severity did not correlate with underlying disease, immune status, or outcome. The majority of patients receiving erythromycin demonstrated objective radiologic improvement. In a patient population that included nonimmunosuppressed patients, nodule formation and rapid radiologic progression were not found to be characteristic of PPA pneumonia.