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Overview

Flu is an acute illness (i.e., comes on suddenly) caused by infection with an influenza virus. The flu affects the upper and lower respiratory tract (e.g., nose, throat, bronchi, lungs) and also causes symptoms that affect the entire body (i.e., systemic symptoms), such as headache, fever, muscle aches (myalgia), and weakness. Infection with the flu virus usually lasts about one week.

In April 2009, the World Health Organization (WHO) raised the pandemic alert to phase 5 in resp...Read the full article