It is anticipated that approximately 33% of the patients enrolled in the Specific Aim 1 clinical study (evidence of infection and two or more SIRS criteria) will have CAP as the underlying infection causing sepsis. Furthermore, it is anticipated that approximately 25% of these CAP patients will develop severe CAP. Specific aim 2 proposes a secondary, separate analysis of all patients enrolled in the Specific Aim 1 clinical study who have CAP in order to identify biomarkers for early diagnosis of severe CAP. We propose to inventory existing candidate biomarkers of severe CAP through literature review. Furthermore, we propose to validate the utility of some of these biomarkers, and to identify a number of novel biomarkers of severe CAP through analysis of the subset of patients in the prospective clinical study who have CAP and employing 2 proteomic technologies (mass spectrometry and multiplexed immunoassays), mass spectrometry-based plasma metabolomics and sequencing of mRNA derived from peripheral blood lymphocytes. Bivariable analyses will be performed to identify plasma biomarker differences between mild and severe CAP. Multivariable analyses will be performed in order to derive a plasma biomarker panel and algorithm for early diagnosis of severe CAP. The biomarker panel for early diagnosis of severe CAP will be compared with established prognostic indices, such as PORT score. Novel biomarkers of severe CAP will be identified by mass spectrometry of patient EDTA plasma samples.