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Influenza, or flu, is a virus that targets the respiratory system. Here are answers to the 10 most common questions about the flu.

1. What is the difference between a cold and the flu?

The flu and the common cold are both respiratory illnesses, but they are caused by different viruses. Influenza or "the flu" develops when a flu virus infects the respiratory system, including your nose, throat, bronchial tubes, and possibly the lungs. A cold virus usually infects only the upper respiratory tract: your nose and throat.

The flu usually causes more severe illness than the common cold. Flu can bring on fever, body aches, and exhaustion, symptoms that are rarely caused by simple colds.

2. What are flu symptoms and when is a person contagious?

Primary symptoms of flu are fever, fatigue, body aches, chills, headache, sore throat, and cough. The cough is a bronchial tube irritation and is usually not productive -- you're not coughing up gunk. The flu is usually at its worst for three to four days. The cough may linger longer. Recovery may take seven to 10 days. You may have lingering fatigue for several weeks.

There's one catch with flu viruses. About 24 to 72 hours after you're infected, you become contagious. Yet you may not have symptoms, so you don't know you're sick. You feel completely healthy and go about your daily affairs -- spreading the virus wherever you go.

Stay at home while you have the flu, and for at least 24 hours after your fever is gone without the use of fever-reducing medicine. Once your fever is gone for a day, you're no longer contagious and can return to work or school. Also, you will recover more quickly if you get some rest.

3. What's the best treatment for flu?

There's no single "best" treatment for flu, but there are many ways you can ease symptoms.

Prescription flu drugs can shorten the time you feel sick if taken when symptoms first appear. They work best when taken within 48 hours of symptoms, but they may also prevent severe disease if taken more than 48 hours after the first symptoms. Over-the-counter cold and flu drugs can offer some relief from fever, aches, stuffy nose, and cough. They don't "cure" the flu, but may help keep you more comfortable.

What can help? Decongestants can help you breathe by shrinking swollen mucous membranes in the nose. Saline nasal sprays can also help open breathing passages. Cough preparations, along with water and fruit juices, can help soothe a cough. If you use a multi-symptom cold medicine, choose the drug that matches your symptoms. And don't take two cold medicines with the same ingredients.

Don’t use over-the-counter cough and cold medicines in children under 4. If your child is between 4 and 6, ask your doctor before giving any medicine. It’s safe to use these drugs to help relieve symptoms in kids 6 and older. Never give medicines with aspirin to young adults and children due to the risk of Reye’s syndrome.

It's very important to drink a lot of fluids to keep the body hydrated. This helps loosen mucus. Limit drinks like coffee, tea, and colas with caffeine. They rob your system of fluids. As for eating, follow your appetite. If you're not really hungry, try eating simple foods like white rice or broth.