According to World Health Organization (WHO), influenza virus infections cause 3-5 million clinically severe cases and 290-650 thousand deaths per year due to solely respiratory disease [1]. Besides its mortality and morbidity, influenza virus infections bring about severe economic burden on health-care systems. Identifying the prognostic factors and early recognition of the severe cases can help reduce these undesired outcomes. Older age, comorbidities (e.g. pulmonary diseases, hearth failure, chronic renal disease, chronic liver disease and diabetes mellitus), immunosuppressive conditions and pregnancy are known as classical risk factors for severe disease and mortality [2,3].
