Legionnaires' disease: a review of the epidemiology and clinical manifestations of a newly recognized infection.

During the 2-year period 1977 through 1979, 26 patients with Legionnaires' disease were seen at the Mayo Clinic and affiliated hospitals. The patients ranged in age from 17 to 81 years with a median of 51 years. Twelve (46%) were immunologically compromised. Most of the other patients had underlying chronic tobacco bronchitis. Hectic fever, cough, and diarrhea were common symptoms. Chest radiographs showed patchy perihilar infiltrates that often progressed to consolidation. Diagnosis was made by indirect fluorescent antibody testing in 15 patients (58%), but in no case was the test diagnostic during the first week of illness. In seven patients the diagnosis was established by positive direct flourescent antibody testing of lung tissue, in two cases by culture of lung tissue, and in one case each by direct fluorescent antibody positivity of sputum or bronchial washing. Of the 26 patients, 3 (12%) required hemodialysis for acute renal failure and 5 (19%) died. A favorable clinical response to therapy with erythromycin was noted. The differential diagnosis of Legionnaires' disease must include other bacterial pneumonias, as well as mycoplasma, psittacosis, Q fever, and viral pneumonia. For critically ill patients, open-lung biopsy may be necessary to provide a rapid diagnosis. Current evidence suggests that erythromycin alone or in combination with rifampin is the treatment of choice. A 3-week course of therapy is recommended in order to prevent relapse.