CAP was defined by the following criteria observed at initial presentation or occurring within 48 h following hospitalization: acute onset of signs and symptoms of lower respiratory tract infection and a new pulmonary infiltrate found on the hospital admission chest radiograph. We excluded patients coming from nursing homes or hospitalized within 90 days prior to developing pneumonia or hospitalized > 48 h in general medical wards before ICU admission, and those with radiographic abnormalities attributed solely to any other known cause (i.e., pulmonary embolus, lung carcinoma or congestive heart failure). The decision for admission to our ICU was made, in all cases, by the attending physicians. However, only patients having a Pneumonia Severity Index (PSI) score ≥ 4 were included in this study [10] .