Interest of Absolute Eosinopenia as a Marker of Influenza in Outpatients during the Fall-Winter Seasons 2016-2018 in the Greater Paris Area: The SUPERFLUOUS Study.

INTRODUCTION

Prior to the emergence of COVID-19, when influenza was the predominant cause of viral respiratory tract infections (VRTIs), this study aimed to analyze the distinct biological abnormalities associated with influenza in outpatient settings.

METHODS

A multicenter retrospective study was conducted among outpatients, with the majority seeking consultation at the emergency department, who tested positive for VRTIs using RT-PCR between 2016 and 2018. Patient characteristics were compared between influenza (A and B types) and non-influenza viruses, and predictors of influenza were identified using two different models focusing on absolute eosinopenia (0/mm) and lymphocyte count <800/mm.

RESULTS

Among 590 VRTIs, 116 (19.7%) were identified as outpatients, including 88 cases of influenza. Multivariable logistic regression analysis revealed the following predictors of influenza: in the first model, winter season (adjusted odds ratio [aOR] 7.1, 95% confidence interval [CI] 1.12-45.08) and absolute eosinopenia (aOR 6.16, 95% CI 1.14-33.24); in the second model, winter season (aOR 9.08, 95% CI 1.49-55.40) and lymphocyte count <800/mm (aOR 7.37, 95% CI 1.86-29.20). Absolute eosinopenia exhibited the highest specificity and positive predictive value (92% and 92.3%, respectively).

CONCLUSION

During the winter season, specific biological abnormalities can aid physicians in identifying influenza cases and guide the appropriate use of antiviral therapy when rapid molecular tests are not readily available.