A comparative study of Legionella micdadei and other nosocomial acquired pneumonia.

The clinical and laboratory characteristics of 27 patients during an outbreak of pneumonia due to Legionella micdadei were reviewed. These patients were compared with a group of 46 patients who had other causes of nosocomial acquired pneumonia. Patients with pneumonia due to L micdadei typically had nosocomial acquisition of the disease and were immunosuppressed. Symptoms, physical findings, and laboratory tests were nonspecific; however, patients with pneumonia due to L micdadei had an increased frequency of pleuritic pain in the chest, dyspnea, cough, and changes in mental status compared to the nosocomial group. Direct fluorescent antibody staining and culture of sputum and other respiratory secretions established the diagnosis of infection with L micdadei. Unusual features included dual infections in three patients and pulmonary cavitation in five patients. Therapy with erythromycin, when instituted early, decreased mortality. Trimethoprim-sulfamethoxazole, used as alternative therapy in patients with persistent infection, was also curative. Because of the high mortality associated with a delay in diagnosis, it is important to consider the diagnosis of pneumonia due to L micdadei in immunosuppressed patients.