Predicting severe disease in patients diagnosed with seasonal influenza in the emergency department.

Objectives: We sought to develop an evidence-based tool to risk stratify patients diagnosed with seasonal influenza in the emergency department (ED). Methods: We performed a single-center retrospective cohort study of all adult patients diagnosed with influenza in a large tertiary care ED between 2008 and 2018. We evaluated demographics, triage vital signs, chest x-ray and laboratory results obtained in the ED. We used univariate and multivariate statistics to examine the composite primary outcome of death or need for intubation. We validated our findings in patients diagnosed between 2018 and 2020. Results: We collected data from 3128 subjects; 2196 in the derivation cohort and 932 in the validation cohort. Medical comorbidities, multifocal opacities or pleural effusion on chest radiography, older age, elevated respiratory rate, hypoxia, elevated blood urea nitrogen, blood glucose, blood lactate, and red blood cell distribution width were factors associated with intubation or death. We developed the Predicting Intubation in seasonal Influenza Patients diagnosed in the ED (PIIPED) risk-stratification tool from these factors. The PIIPED tool predicted intubation or death with an area under the receiver operating characteristic curve (AUC) of 0.899 in the derivation cohort and 0.895 in the validation cohort. A version of the tool including only factors available at ED triage, before laboratory or radiographic evaluation, exhibited AUC of 0.852 in the derivation cohort and 0.823 in the validation cohort. Conclusion: Clinical findings during an ED visit predict severe outcomes in patients with seasonal influenza. The PIIPED risk stratification tool shows promise but requires prospective validation.