on those of the CDC/NNIS system. An infection was deemed device‐associated when the day of or the day before the infection occurred was a device day. All patients who stayed at the ICU for 48 hours or more were included in the surveillance and followed from admission until discharge, death, or the day of withholding treatment because of their moribund condition. The study period per patient was restricted up to 56 days. After discharge from the ICU patients were followed‐up for infection for another 24 h. The surveillance included 4,105 patients, for 3,921 of whom sufficient data were available. Of these patients 1,277 (33%) had an infection when entering the ICU and were analyzed separately (data not shown). The remaining 2,644 patients remained at the ICU for a total of 25,432 days. Median ICU stay was 6 days, interquartile range (IQR) 6 days. Patient characteristics of patients with and without a device‐associated infection are presented in the Electronic Supplementary Material (ESM; Appendix A). The following patient characteristics were recorded: demographic data, medical discipline treating the patient (specialty), Acute Physiology and Chronic Health Evaluation (APACHE) II score, immunity status (normal immunity, leukopenia (leukocytes polymorphonuclear cells < 0.5 x 109/l), and otherwise impaired immunity (defined as a chronic low or recent high dose of corticosteroids, chemotherapy, dialysis or systemic diseases such as leukemia or AIDS in patients with leukocytes polymorphonucelair cells > 0.5 x 109/l), origin (e.g. community, ward) and whether admission was acute or elective. The use of medical devices (mechanical ventilation (including intubation without ventilation and/or having a tracheostoma); CVC and indwelling transurethral or suprapubic catheter), systemic antibiotics and selective decontamination of the digestive tract (SDD) were recorded daily. Two or more central venous catheters on 1 day were counted as one CVC day. For each nosocomial infection the infection date, type of infection, and microbiological test result were recorded. Pneumonias registered within 4 days from an earlier pneumonia in the same patient, and sepsis and UTI occurring within 7 days after the same kind of infection were not regarded as new infections, according to the European protocol for nosocomial infection surveillance [6]. This led to the exclusion of about 2.5% of infections but did not affect the calculation of risk factors, as only the first VAP, CR‐BSI, or CA‐UTI was included in the regression analysis. Any new pathogens with these excluded infections were presented with the former infection. In patients who developed a device‐related infection the time at risk was defined as the number of days from the first day the device was used until the day on which the device‐related infection was diagnosed or, if no infection occurred, until the last day of device use. Observations were censored if the device was no longer used or if the patients with the device were transferred to other hospitals, deceased or when active (life‐supporting) treatment was 24 Chapter 2
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