[Community-acquired pneumonia due to Legionella pneumophila serogroup 1. Study of 97 cases]

Legionella pneumophila is the causal agent of 5% to 12% of sporadic community-acquired pneumonia cases, though rates are changing with the use of new diagnostic methods.This is a retrospective study of all patients admitted to our hospital with community-acquired pneumonia due to Legionella pneumophila between 1997 and 2001. Diagnostic criteria included either a positive Legionella serogroup 1 urinary antigen test or seroconversion and a chest radiograph consistent with pneumonia.A total of 97 patients were studied. Ninety cases (92.8%) were community-acquired and 7 (7.2%) were associated with travelling. In 82 cases (84.5%) the presentation was sporadic. Seventy-five patients were smokers (77.3%). The most common symptoms were fever in 91 patients (93.8%) and cough in 67 (68.1%). In five patients (5.2%) creatine phosphokinase concentrations were over 5 times their baseline values (in two over 100 times); four of these patients presented acute renal failure. Seroconversion was observed in 23/42 patients (54.8%). There were no statistically significant differences between the administration of erythromycin or clarithromycin in monotherapy, or in combination with rifampin. Nineteen patients (19.6%) presented acute renal failure and mechanical ventilation was necessary in 22 (22.7%). Twelve patients died (12.5%). Independent prognostic factors associated with death included respiratory rate30 breaths/min, urea60 mg/dL and PaO260 mmHg. A significant linear association was found between severity scale scores and the presence of complications or mortality.The Legionella urinary antigen test permits early diagnosis and treatment of this disease. The severity scale is an indicator of complications or death.