Influenza

The symptoms of influenza (flu) appear suddenly and often include:

• Fever of 100° F (37.8° C) to 104° F (40° C) , which can reach 106° F (41° C) when symptoms first develop. Fever is usually continuous, but it may come and go. Fever may be lower in older adults than in children and younger adults. When fever is high, other symptoms usually are more severe.
• Body aches and muscle pain (often severe), commonly in the back, arms, or legs.
• Headache.
• Pain when you move your eyes.
• Fatigue, a general feeling of sickness (malaise), and loss of appetite.
• A dry cough, runny nose, and dry or sore throat. You may not notice these during the first few days of the illness when other symptoms are more severe. As your fever goes away, these symptoms may become more evident.

Influenza usually does not cause symptoms in the stomach or intestines, such as vomiting and diarrhea.

Other conditions have symptoms similar to the flu, such as the common cold, bacterial infections, and infectious mononucleosis.