The flu virus attacks your respiratory system. This leads to the symptoms you commonly experience with the flu. Some signs and symptoms, such as a runny nose, sneezing and sore throat, may initially seem like a common cold. But if you are an adult and have a fever of 101 F or more, you may have influenza. Your fever may last from one day to as long as a week and, in rare cases, may reach as high as 106 F.

You're also likely to feel much worse with the flu than with a cold. Although you can probably carry on with a cold, the flu can knock you flat. Even after you've recovered, you may still feel tired.

Other signs and symptoms of influenza include:

• Chills and sweats

• Headache

• Dry cough

• Muscular aches and pains, especially in your back, arms and legs

• Fatigue and weakness

• Nasal congestion

Loss of appetite. Children with the flu tend to have higher fevers than infected adults have — often 103 to 105 F. Influenza may also cause children to feel nauseous and experience vomiting and diarrhea.

The flu virus typically has an incubation period of one to four days, although symptoms usually come on suddenly. In most cases, you should feel better in about a week to 10 days unless you develop a serious post-flu lung infection, such as bacterial pneumonia or subacute bronchitis — an inflammation of the lining of your bronchial tubes.

If you've been infected with the flu, you can spread the disease to others before you realize you're sick and for as long as a week after your symptoms appear.

Distinguishing flu from other ailments
Although other viral infections, especially colds and intestinal ailments such as gastroenteritis — a condition that causes diarrhea, nausea and vomiting — are often referred to as the flu, they're not. Real influenza usually doesn't affect your intestines. And while you may cough and sneeze with the flu, you're also likely to have a high fever, chills and body aches — signs and symptoms you won't typically have with a cold.

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