Comparison of clinical outcomes in critically ill COVID-19 patients on mechanical ventilation with nosocomial pneumonia between Alpha and Omicron variants

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19), a pandemic that has resulted in millions of deaths worldwide. Critically ill COVID-19 patients who require intubation and develop nosocomial pneumonia, commonly caused by gram-negative bacilli, have a higher mortality rate than those without nosocomial pneumonia. Objectives: The aim of this study is to compare the clinical characteristics and outcomes and associated risk factors of Alpha and Omicron SARS-CoV-2 variants in critically ill patients on mechanical ventilation (MV) with nosocomial pneumonia. Design: This is a retrospective single-center cohort study. Methods: This observational study was conducted at Taipei Veterans General Hospital, Taiwan from May 2021 to September 2022. Critically ill patients who had confirmed SARS-CoV-2 infection and intubated on a MV with bacterial pneumonia were enrolled. Demographic data, laboratory results, and treatment information were collected and analyzed. In addition, clinical outcomes among different SARS-CoV-2 variants were examined. Results: This study included 94 critically ill COVID-19 patients who required intubation and intensive care unit (ICU) admission. The Alpha group had a longer duration of SARS-CoV-2 viral shedding, MV days, and ICU stay, while the Omicron group had older age, more comorbidities, higher APACHE II scores, and higher in-hospital mortality (47.0% versus 25.0%, p = 0.047). However, independent risk factors for in-hospital mortality included malignancy, lower serum albumin levels, and lack of Remdesivir treatment, except for the SARS-CoV-2 variant. Conclusion: Our study discovered a higher in-hospital mortality rate in severe COVID-19 patients with MV and secondary pneumonia infected with the Omicron variant compared to the Alpha variant; however, real independent risk factors for in-hospital mortality are malignancy, lower serum albumin level, and lack of Remdesivir treatment.