<qa>  What is the average ICU size?Based on an earlier study, about the 40 of the admitted patients have a length of stay shorter than 3 days and the incidence of infections was 30. For this reason its calculate to be necessary to include 2928 patients to have an alpha error 0,01 and a beta error 0,01, excluding every patient with an ICU stay shorter than 72 hours. Considering the variability in the length of ICU stay in the single ICUs and the possibility that on the date of 31032017 some ICUs could not reach the possibility of admitting 300 patients, the theorical sample size is expanded to 3300 patients in total 20 of the theorical sample. 