Influenza (the flu) is a common viral respiratory infection that causes an illness ranging from mild to severe, and sometimes can be fatal. Influenza testing detects the presence of the virus in a sample of respiratory secretions.
Influenza tends to be seasonal, usually beginning in late fall and disappearing in early spring. According to the Centers for Disease Control and Prevention (CDC), influenza affects millions of Americans each season. Signs and symptoms like headache, fever, chills, muscle pains, exhaustion, a stuffy nose, sore throat, and a cough tend to be more severe and longer lasting than the symptoms caused by the common cold.