 Bloodstream infections BSI are a major cause of morbidity and mortality. Community-onset BSI have an overall attributable mortality of 10-13 while nosocomial BSI mortality ranges are quite variable from 12-80. Bloodstream infections are also costly and result in prolonged hospital stays. Nosocomial BSIs have been shown to increase length of stay by 5-25 days and increase costs 23,000 - 40,000 above matched controls. The duration of therapy necessary to clear blood stream infections is unknown and no study has systematically addressed this issue. The use of antimicrobials is also not without consequence. These include financial cost, side-effects, promotion of superinfection especially Clostridium difficile-associated diarrhea, and the promotion of microbial resistance. We hypothesize that a procalcitonin host biomarker and endotoxin microorganism biomarker-guided treatment plan could significantly decrease unnecessary exposure to antibiotics in patients with bloodstream infections. 