Retrospective Single-center Cohort Study to Evaluate the Incidence of Colonization by Multidrug-resistant Organisms in Mechanically Ventilated Patients With Severe COVID-19 Admitted to a Large Intensive Care Unit in Milan, Italy

Bacterial superinfection represents a major treat for patients admitted to intensive care unit (ICU), severely impacting clinical outcome and length of hospital stay. Several studies showed that previous multidrug-resistant organisms (MDRO) colonization is a major risk factor for subsequent infection. The coronavirus disease 2019 (COVID-19) pandemic caused an unprecedented rate of ICU admissions and drastically changed the ICU care itself, in terms of infection control measures and therapeutic usage of immunomodulating drugs. Depending on the study, incidence of bacterial infections acquired in COVID-19 ICUs ranges from 12% to 50%. In a retrospective, multicenter study conducted in 8 Italian ICUs during the first wave of the pandemic (March 2020-May 2020), 46% of the patients developed a bacterial superinfection. Notably, 35% of these infections were caused by MDRO. To date there is still scarce evidence on the incidence of colonization by MDRO in patients admitted to COVID-19 ICUs, and little data has been collected on risk factors associated with MDRO colonization. Based on case series analysis, MDRO colonization has been associated with presence of invasive devices, prolonged ICU stay and use of corticosteroids and antibiotics.

The Milano Fiera ICU was a large, modular, COVID-19 ICU built in Milan, Italy, in March 2020 to face the impact of the pandemic. It was composed of distinct units (modules) to accommodate up to 100 patients with severe SARS-CoV-2 infection requiring mechanical ventilation. Since October 2020, over 400 mechanically ventilated COVID-19 patients were admitted to Milano Fiera ICU. Despite each module was managed by staff coming from different hospitals in the Milan area, microbiological surveillance was standardized, and all modules referred to the Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico of Milan for laboratory analysis and infectious disease specialist consultation.

The present retrospective single-center cohort study aims to evaluate the incidence of colonization by MDRO in patients admitted to the Milano Fiera ICU during the second wave of COVID-19 pandemic (October 2020-May 2021). Furthermore, the study will evaluate the overall incidence of infections during the ICU stay and analyze the risk factors associated with bacterial superinfection and with MDRO colonization.