Secondary infections in critically ill patients with viral pneumonia due to COVID-19 and influenza: a historical cohort study

PURPOSE: To compare the incidence and nature of secondary infections (SI) between critically ill patients with viral pneumonia due to COVID-19 and seasonal influenza and explore the association between SI and clinical outcomes. METHODS: We conducted a historical cohort study of patients admitted to the intensive care unit (ICU) at two tertiary care centers during the first wave of the COVID-19 pandemic and patients admitted with influenza during the 2018–2019 season. The primary outcome was the rate of SI. Secondary outcomes included rates of ICU and in-hospital mortality, organ-support-dependent disease, and length of ICU and hospital stay. RESULTS: Secondary infections developed in 55% of 95 COVID-19 patients and 51% of 47 influenza patients (unadjusted odds ratio [OR], 1.16; 95% confidence interval [CI], 0.57 to 2.33). After adjusting for baseline differences between cohorts, there were no significant differences between the COVID-19 cohort and the influenza cohort (adjusted OR, 1.00; 95% CI, 0.41 to 2.44). COVID-19 patients with SI had longer ICU and hospital stays and duration of mechanical ventilation. The SI incidence was higher in COVID-19 patients treated with steroids than in those not treated with steroids (15/20, 75% vs 37/75, 49%). CONCLUSION: Secondary infections were common among critically ill patients with viral pneumonia including COVID-19. We found no difference in the incidence of SI between COVID-19 and influenza in our cohort study, but SI in patients with COVID-19 were associated with worse clinical outcomes and increased healthcare resource use. The small cohort size precludes any causal inferences but may provide a basis for future research. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12630-022-02376-0.