infectious diseases
Influenza
Introduction
Influenza is a Overview of Viral Respiratory Infections causing fever, coryza, cough, headache, and malaise. Mortality is possible during seasonal epidemics, particularly among high-risk patients (eg, those who are institutionalized, at the extremes of age, have cardiopulmonary insufficiency, or are in late pregnancy); during pandemics, even healthy, young patients may die. Diagnosis is usually clinical and depends on local epidemiologic patterns. The influenza vaccine should be given annually to everyone aged ≥ 6 months who does not have a contraindication. Antiviral treatment reduces the duration of illness by about 1 day and should be specifically considered for high-risk patients. Influenza refers to illness caused by the influenza viruses, but the term is commonly and incorrectly used to refer to similar illnesses caused by other viral respiratory pathogens. Influenza viruses are classified as type A, B, or C by their nucleoproteins and matrix proteins. Influenza C virus infection does not cause typical influenza illness and is not discussed here. 