Previously healthy patients presenting to UNC with respiratory failure presumptively caused by a primary lung infection will be screened. Only those patients intubated within 48-hours of potential enrollment and between the ages of ≥37 weeks gestation and 17 years will be considered. For purposes of this study, acute respiratory illness is defined as having upper respiratory infection symptoms and/or lower respiratory tract infection. Patient should have fever (>38 oC) OR leukocytosis / leukopenia (>10,000 or <2,000) AND any of the following: tachypnea, hypoxia (saturation <97%), cough, congestion, rhinorrhea, abnormal lung exam findings, or infiltrate on chest x-ray.