Introduction

The influenza virus remains a serious threat to the global health system given the occurrence of three to five million severe cases per year and the high number of mortalities, particularly during pandemics1,2. This virus gives rise to a disease with manifestations that are common to some other infections, such as fever, malaise, and headache 3,4. Three types of influenza viruses affect humans: A, B, and C 5. Based on the alterations in the hemagglutinin and neuraminidase surface proteins, the type A influenza virus is divided into numerous subtypes. The H3N2 and H1N1 subtypes of influenza A have received considerable attention in recent years. A critical issue that gives rise to major challenges is the mutations that occur in the various influenza virus strains, particularly in the A-H3N2 and A-H1N1 subtypes and the B type6-8.
In the clinic, it is usually impossible to differentiate infection triggered by various types and subtypes of influenza according to the clinical manifestations 9,10. Fever is the most commonly reported sign that presents in more than 90% of patients11,12. Respiratory complications, gastrointestinal involvement, cardiovascular involvement, and constitutional complaints (e.g., myalgia, malaise, and fatigue) are some of the other signs and symptoms of influenza virus infection (10). The radiological characteristics of subjects with various types of influenza, especially the 2009 H1N1 strain, have been reported in the previous surveys, where differences between patients of mild and severe disease have been discussed. The main findings obtained from radiological investigations on influenza subjects are ground-glass opacities, areas of consolidation, or a mixed pattern of these two findings (11, 12). In this cross-sectional study, we retrospectively evaluated the thoracic CT findings, serological biomarkers, and clinical features in cases with confirmed A-H1N1, B- H1N1, and A-H3N2 virus infection.