The radiologic manifestations of Legionnaire's disease. The Ohio Community-Based Pneumonia Incidence Study Group.

STUDY OBJECTIVES: To study the serial radiographic manifestations of Legionnaire's disease from the initial presentation on admission to recovery using strict criteria for the diagnosis of infection.

MATERIALS AND METHODS: We prospectively studied the chest radiographs of patients hospitalized with a diagnosis of community-acquired pneumonia in Summit County, Ohio between November 1990 and November 1992. Forty-three patients fulfilled strict criteria for legionellosis. The diagnosis of infection was based on the criteria of "definite" diagnosis as defined by the Ohio Community-Based Pneumonia Incidence Study Group report. The criteria included the isolation of the microorganism, the presence of a significant antibody rise, or the presence of Legionella antigen in the urine.

RESULTS: Forty of 43 patients had admission radiographs interpreted as compatible with pneumonia. In spite of appropriate antimicrobial therapy, worsening of the infiltrates was found in more than half of the patients within the first week. Twenty-seven patients were observed to have pleural effusion during the course of hospitalization: 10 effusions were found on admission, another 14 developed during the first week, and 3 new effusions were discovered after the first week. Cavitation was found in only one patient. None of the patients had apical involvement.

CONCLUSION: This study confirms previous reports using less stringent etiologic diagnosis criteria that chest radiographic findings in Legionnaire's disease are not specific. Even with appropriate therapy, more than half of the patients will have worsening of the infiltrates during the first week. Pleural effusion is common among our patients, and it is frequently detected during the serial radiographic studies during the first week of hospitalization. Chest radiography in Legionnaire's disease is useful only for the monitoring of disease progression and not for diagnostic purposes. In addition, worsening of infiltrates and pleural effusion are seen in more than half of the patients in spite of appropriate therapy and clinical improvement.