In this observation trial, all consecutive admissions to the Department of Critical Care and Pulmonary Services on predetermined and randomly selected emergency duty days were eligible. Inclusion criteria were: i) age above 16 yrs, ii) written informed consent; iii) acute respiratory illness and iii) presence of new pulmonary infiltrates or pleural effusion on chest x-ray or lung computed tomography. Exclusion criteria were: i) Human immunodeficiency virus (HIV) infection, ii) documented extrapulmonary infection, iii) neutropenia; and iv) oral intake of corticosteroids defined as any more than 1 mg/kg of prednisone for more than 1 month. The study protocol was approved by the Ethics Committee of the hospital and written informed consent was obtained from all patients within the first 12 hrs after admission.