PCT samples were collected for 14 days or until patients were discharged from the ICU and/or no longer required any mechanical ventilatory support. Blood samples not expected to be analyzed within 24 h of collection were frozen at -20°C for later analysis. PCT was measured using an immunoluminometric assay (LUMItest ® ; BRAHMS GmbH, Hennigsdorf, Germany). PCT levels were not available to the investigators until completion of the study and had no impact upon patient care during the course of the study.