Study population and design
From January 2018 to December 2018, 1381 patients (≥18) undergoing cardiac surgery were transferred to our cardiac surgical ICU. All of them were eligible for the investigation except for those who died within 24 hours postoperatively (n=21). All patients received standard postoperative care complied with published guidelines [4,5]. Antibiotic prophylaxis was a single second generation cephalosporin. Body temperature was recorded every 6 hours routinely and anytime when necessary. Haematologic tests and chest radiographs were performend regularly. Microbiological examinations of the sputum, blood, catheter tips and excretion of these patients were performed as clinically indicated to isolate pathogens according to the criteria of Clinical and Laboratory Standards Institute (CLSI). One pathogen cultured positively more times in the same patient within one week was regarded as one.