- Independent variables for Study 1: demographics, comorbidities in adults (Charlson's index), comorbidities in children (ARPEC PPS definitions), type of acquisition, systemic inflammatory response syndrome severity in adults, sepsis criteria in children, Pitt score, SOFA score, APACHE-II score, PIM2, invasive procedures, neutropenia, microbiological variables (poly or monomicrobial infection, carbapenemase producer, carbapenemases type, susceptibility profile, carbapenem MIC), clinical management (source control and support therapy), antimicrobial therapy.