Clinical utility of severity scores in identifying severe influenza

Seasonal influenza can cause substantial morbidity and mortality, but for most patients it is self-limiting with low risk of complications. We aimed to investigate the outcome of hospitalized adults with confirmed influenza and assess the clinical utility of previously developed scoring systems for risk stratification of severe influenza-associated illness in the Emergency Department.

A retrospective observational cohort study was conducted on adults hospitalized with laboratory-confirmed influenza between 2015 and 2019. Severe influenza-associated illness was defined as requiring high-flow oxygen therapy, non-invasive ventilation, invasive mechanical ventilation, or resulting in in-hospital mortality. The following severity scores were assessed: CRB-65, DS-CRB-65, NEWS2, NEWS-C, qNEWS, qSOFA, and SSTS.

Out of 735 patients, 70 (10 %) developed severe influenza-associated illness. Radiological signs suggestive of pneumonia were more frequent in this group. A NEWS2 score of ≥7 demonstrated the highest overall accuracy (AUC 0.76, 95 % CI 0.64-0.77) among the evaluated scores in identifying patients at risk of developing severe influenza-associated illness. Multivariate analysis identified respiratory rate ≥ 30, oxygen saturation < 90 %, and C-reactive protein (CRP) ≥100 mg/L as independent predictors for severe influenza-associated illness.

Severe influenza-associated illness is common among adults hospitalized with influenza. No severity score could effectively identify high-risk patients across the entire study population. NEWS2 showed promising results for patients under 65 years old. Patients with low risk of developing severe influenza-associated illness can potentially be identified at presentation by combining NEWS2 with CRP but prospective studies are needed to confirm its utility in managing influenza in acute care.