<qa>  What is the main purpose of the study?The purpose of this study is to examine the immune response to traumatic injury and subsequent infections in critically ill adults. Traumatic injuries lead to severe dysregulation of the immune system, and predispose to severe infections. Diagnosing these infections in a timely manner is paramount in reducing morbidity and mortality, but diagnosis is made difficult by the inflammatory response to trauma. The main purpose of the study is to prospectively test the diagnostic power of the expression of an 11-gene set which the investigators recently published Sweeney et al., Sci Transl Med, 2015. Since the timing of an acquired infection cannot be determined a priori, this study is designed to be a longitudinal examination of a cohort of traumatically injured adults. The investigators will draw blood at regular intervals, as well as at day of diagnosis of infection for any patient that are diagnosed with an infection. The investigators will then assay the blood for gene expression levels post hoc, and correlate the molecular profiles with clinical information to establish a prospective estimate of diagnostic power. 