Influenza in Adults Seeking Care at Seven European Emergency Departments: A Prospective Active Surveillance During the 2019-2020 Influenza Season.

Background: Influenza can be associated with nonrespiratory disease presentation, but these are less well documented due to the lack of routine testing for influenza in the healthcare system, especially if patients do not present with influenza-like illness (ILI). We aimed to measure the proportion of influenza cases seeking care at emergency department (ED) for a nontraumatic cause, to describe their clinical presentation and their ED-discharge diagnosis.

Methods: The study was conducted at seven hospitals in France, Spain, Italy and Germany during the 2019-20 influenza season, for a period of 10 weeks. Patients (≥ 18 years) consulting for nontraumatic causes at the ED were invited to participate. Consenting patients provided upper respiratory swab samples for influenza testing by reverse transcription polymerase chain reaction. Clinical and demographic data were collected.

Results: There were 8678 patients included, 50.7% were female and the median age was 57 years. Among them, 494 (5.7%) were laboratory-confirmed influenza (LCI) cases. Nonetheless, only 24.3% of LCI cases had an ED-discharge of influenza. Of all cases confirmed as influenza, 47.6% had a nonrespiratory discharge diagnosis, which frequency increased with age. ILI case definition from the European Centre for Disease Prevention and Control was the most frequently met among influenza cases (68.6%). Older patients (≥ 65 years) were less frequently identified based on any ILI signs/symptoms.

Conclusion: Our findings indicate that the impact of influenza among patients seeking care at the ED cannot be easily assessed based on clinical presentation and medical records alone. Preventing influenza among adult population may reduce healthcare utilization.