Since the symptoms of an influenza infection are very different from the common cold, the diagnosis can be made fairly quickly. A doctor will be able to tell that you have the flu if you have at least some or most of these symptoms:

• high fever
• aches and pains everywhere, especially in the back and legs
• bad headache
• sensitivity to light
• red and watery eyes and a runny nose
• nauseous feeling and possible vomiting
• dry cough at first, then bringing up sputum
• burning sensation in the chest

If there is any doubt, a doctor can make sure that it's the flu by taking a sample of your sputum and testing it for the virus. This is rarely needed.