Procalcitonin Level to Discontinue Antibiotics on ICU Patients With no Obvious Site of Infection

Inclusion Criteria: * Suspected infection (no clear-cut source of infection) as defined by the treating physician * Empiric antibiotic treatment * No clear-cut source of infection by clinical or microbiological criteria * ICU patient * Informed consent Exclusion Criteria: * Age \<18 years * Pregnancy * Hemodynamic instability defined as persistent hypotension, need for on-going aggressive resuscitation and/or vasopressor support to maintain an adequate mean arterial blood pressure * Need for antibiotic prophylaxis * Patient withdrawn from empiric antibiotic treatment before Day 4 * Severely immuno-compromised patient (liver cirrhosis (Child-Pugh class C), immunosuppressive drugs after transplantation, neutropenia (absolute neutrophil count \<1000 counts/L), CD-4 count less than 200) * Patient with suspected bacterial or fungal endocarditis * Patient with suspected meningitis * Cardiopulmonary bypass within the last 7 days1) * Major surgery within the last 7 days (surgery that induces a major inflammatory response such as heart or aortic surgery or major abdominal surgery (i.e. duodenopancreatectomy) or any surgery requiring massive blood transfusion.) * Multiple trauma within the last 7 days * Cardiopulmonary resuscitation (CPR) within the last 7 days * Burns \>20% body surface area * Patient in terminal status referred for palliative care * Patient with advanced directives or Do Not Resuscitate (DNR) orders * Patient who is already enrolled in another therapeutic clinical study