Incidence of Bacterial Pulmonary Superinfections in critically ill COVID-19 Patients across different waves on the Intensive Care Unit of the University Hospital Zurich

Abstract

Introduction: The global pandemic of the Coronavirus disease 2019 caused by the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) resulted in mil- lions of severe and critical cases. It is well known that patients hospitalised on the intensive care unit have a higher risk of acquiring bacterial superinfections. In the case of critically ill COVID-19 patients these are still rarely systematically reported and ana- lysed. The aim of this study is to determine the incidence of bacterial pulmonary su- perinfections in critically ill COVID 19 patients hospitalised on the intensive care unit at the University Hospital Zurich during the different waves in Switzerland and identify the most common causative microorganisms.
Methods: In this retrospective monocentric cohort study, 149 patients were included and assessed for bacterial superinfection by systematic sampling of blood cultures, tracheobronchial secretions and bronchoalveolar lavages as well as evaluation of the clinical status.
Results: Out of the 149 patients, 70 (47%) were diagnosed with a pulmonary superin- fection The overall risk of developing a relevant superinfection was lower for the sec- ond and later pandemic waves with a subhazard ratio of 0.604 (p = 0.109, 95% CI = 0.33 to 1.12). Among all the superinfected patients the most frequently identified mi- croorganisms were Enterobacter cloacae (13.0%), Klebsiella pneumoniae (11.3%) and Pseudomonas aeruginosa (10.4%). Multidrug resistant bacteria were found in 18 (25.7%) patients with pulmonary superinfection over the course of the pandemic with Pseudomonas aeruginosa (2.7%), Escherichia coli (2%) and Burkholderia spp. (4%) being the most common multidrug resistant pathogens.
Conclusion: The reported incidence of superinfection is high. Compared to the first wave, superinfection rates are declining during the second and later waves. Gram- negative pathogens were prevalent during the first three pandemic surges and are most commonly responsible for causing superinfection. A decrease in multidrug re- sistant pathogens was noted.