KInetics of Procalcitonin to Reduce Unnecessary aNtibiotic Use - Comparing Procalcitonin Kinetics-guided and Absolute Procalcitonin Value-guided Antibiotic Initiation in Reducing Unnecessary Antibiotic Use in Critically Ill Patients

Inclusion Criteria: * Adult (18 years \< ) non-surgical, surgical, or trauma patients * Suspected new-onset infection on admission or during ICU stay * The source of infection is known or highly suspected, and source control has been implemented if needed (i.e., removal of an infected device (e.g., central line, endoprosthesis) * Two PCT values are available - one on the day of suspicion of infection and one 24±4 hours earlier. * Microbiology sampling has to be performed (according to all presumed sources - blood culture -aerobic and anaerobic, lower respiratory tract sample (tracheal aspirate/bronchoalveolar lavage), urine, etc.). * Written informed consent of the patient (or legal guardian if the patient cannot provide consent) Exclusion Criteria: * Septic shock (hypotension requiring vasopressor therapy to maintain mean blood pressure of 65 mmHg or greater and having a serum lactate level greater than 2 mmol/L after adequate fluid resuscitation) * Infections for which long-term antibiotic treatment is strongly recommended (e.g., infective endocarditis, osteoarticular infections, chronic prostatitis, tuberculosis) * Infections related to primary surgical intervention and adequate source control cannot be guaranteed (e.g., fecal peritonitis, pancreatic necrosectomy, infective necrotizing fascitis - i.e., Fournier's gangrene), * Indisputable infections (e.g., hepatic abscess, empyema) * Poor chance of survival (i.e., expected ICU stay less than 24 hours or initial Acute Ph…