what are the causes and symptoms of influenza?
['Sudden onset of high fever.', 'Headache, muscle aches and joint pain.', 'Cough (usually dry)', 'Chills.', 'Sore throat.', 'Nasal congestion and runny nose.', 'Fatigue.', 'Stomach symptoms such as nausea, vomiting or diarrhea may occur but are more common in children than adults.']