[The flu in its worse forms]

Influenza A and B infections are marred with variable morbidity and, in some cases, develop into severe or even fatal respiratory, circulatory and neurologic complications. Respiratory complications are most common and involve primary-Influenza pneumonia and pneumonia from bacterial or fungal superinfections. Nonrespiratory complications can affect several organs/systems, namely the heart (myocarditis, type 1 and 2 myocardial infarction) and the nervous system (stroke, encephalitis, Guillain-Barré Syndrome). This article provides an overview of the basic pathophysiological aspects of Influenza virus infection, reviews the main severe respiratory and nonrespiratory complications and discusses the different treatments with their respective indications, contraindications and limitations.