Performance of established disease severity scores in predicting severe outcomes among adults hospitalized with influenza-FluSurv-NET, 2017-2018

Abstract

Background: Influenza is a substantial cause of annual morbidity and mortality; however, correctly identifying those patients at increased risk for severe disease is often challenging. Several severity indices have been developed; however, these scores have not been validated for use in patients with influenza. We evaluated the discrimination of three clinical disease severity scores in predicting severe influenza-associated outcomes.

Methods: We used data from the Influenza Hospitalization Surveillance Network to assess outcomes of patients hospitalized with influenza in the United States during the 2017-2018 influenza season. We computed patient scores at admission for three widely used disease severity scores: CURB-65, Quick Sepsis-Related Organ Failure Assessment (qSOFA), and the Pneumonia Severity Index (PSI). We then grouped patients with severe outcomes into four severity tiers, ranging from ICU admission to death, and calculated receiver operating characteristic (ROC) curves for each severity index in predicting these tiers of severe outcomes.

Results: Among 8252 patients included in this study, we found that all tested severity scores had higher discrimination for more severe outcomes, including death, and poorer discrimination for less severe outcomes, such as ICU admission. We observed the highest discrimination for PSI against in-hospital mortality, at 0.78.

Conclusions: We observed low to moderate discrimination of all three scores in predicting severe outcomes among adults hospitalized with influenza. Given the substantial annual burden of influenza disease in the United States, identifying a prediction index for severe outcomes in adults requiring hospitalization with influenza would be beneficial for patient triage and clinical decision-making.

Keywords: disease severity; hospitalization; influenza; mortality.

FIGURE 1

Selection of cases for analysis of influenza‐associated hospitalizations, FluSurv‐NET, 2017–2018. This schematic defines the strategy used for the inclusion of cases for analysis of influenza disease severity. There were 27,523 adults hospitalized with influenza in the FluSurv‐NET network during the 2017–2018 influenza season. A portion of patients were sampled for inclusion in this analysis, and case report forms were completed for a selection of these patients. Patients were subsequently excluded if they were determined to have developed a nosocomial influenza infection, if vital sign data were missing, or if outcome data was absent, yielding a final analytic dataset of 8252 individuals.

FIGURE 2

Receiver‐operator characteristic curves for PSI, QSOFA, and CURB‐65 against selected outcome tiers, FluSurv‐NET, 2017–2018. The receiver‐operator characteristic (ROC) curves for PSI, QSOFA, and CURB‐65 are plotted against patients who experienced four tiers of severe outcomes. Tier 1 includes patients whose disease resulted in in‐hospital mortality; Tier 2 includes those patients in Tier 1 as well as those patients who required vasopressors, invasive mechanical ventilation, or extracorporeal membrane oxygenation (ECMO); Tier 3 includes patients in Tier 2 as well as patients who required non‐invasive respiratory support (CPAP, BiPAP, or HFNC); Tier 4 includes patients in Tier 3 as well as patients who required admission to the intensive care unit (ICU).