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Influenza: the Disease

Influenza (Flu)

Influenza, also known as the flu, is a contagious disease that is caused by the influenza virus. It attacks the respiratory tract in humans (nose, throat, and lungs). The flu is different from a cold. Influenza usually comes on suddenly and may include these symptoms:

• Fever
• Headache
• Tiredness (can be extreme)
• Dry cough
• Sore throat
• Nasal congestion
• Body aches

These symptoms are usually referred to as "flu-like symptoms."

Anyone Can Get the Flu, But the Disease Is More Severe for Some People

Most people who get influenza will recover in one to two weeks, but some people will develop life-threatening complications (such as pneumonia) as a result of the flu. Millions of people in the United States - about 10% to 20% of U.S. residents - will get influenza each year. An average of about 36,000 people per year in the United States die from influenza, and 114,000 per year have to be admitted to the hospital as a result of influenza. Anyone can get the flu (even healthy people), and serious problems from influenza can happen at any age. People age 65 years and older, people of any age with chronic medical conditions, and very young children are more likely to get complications from influenza. Pneumonia, bronchitis, and sinus and ear infections are three examples of complications from flu. The flu can make chronic health problems worse. For example, people with asthma may experience asthma attacks while they have the flu, and people with chronic congestive heart failure may have worsening of this condition that is triggered by the flu.

How the Influenza Virus Is Passed Around

The flu is spread, or transmitted, when a person who has the flu coughs, sneezes, or speaks and sends flu virus into the air, and other people inhale the virus. The virus enters the nose, throat, or lungs of a person and begins to multiply, causing symptoms of influenza. Influenza may, less often, be spread when a person touches a surface that has flu viruses on it - a door handle, for instance - and then touches his or her nose or mouth.

The Flu Is Contagious

A person can spread the flu starting one day before he or she feels sick. Adults can continue to pass the flu virus to others for another three to seven days after symptoms start. Children can pass the virus for longer than seven days. Symptoms start one to four days after the virus enters the body. Some persons can be infected with the flu virus but have no symptoms. During this time, those persons can still spread the virus to others.

How To Know if You Have the Flu

Your respiratory illness might be the flu if you have sudden onset of body aches, fever, and respiratory symptoms, and your illness occurs during November through April (the usual flu season in the Northern Hemisphere). However, during this time, other respiratory illnesses can cause similar symptoms and flu can be caught at any time of the year. It is impossible to tell for sure if you have the flu based on symptoms alone. Doctors can perform tests to see if you have the flu if you are in the first few days of your illness.

What You Should Do If You Get the Flu

• Rest
• Drink plenty of liquids
• Avoid using alcohol and tobacco
• Take medication to relieve the symptoms of flu

Influenza is caused by a virus, so antibiotics (like penicillin) don't work to cure it. The best way to prevent the flu is to get an influenza vaccine (flu shot) each fall, before flu season.

Using Flu Shots to Prevent and Control the Flu

A lot of the illness and death caused by the flu can be prevented by yearly flu shots. People in certain groups who are at high risk to develop serious complications from the flu and people who are in close contact with those at high risk should get a flu shot every year.

To find out more about flu shots, see:

Who Should and Who Should not Get a Flu Shot
Flu Shot Information

Avian Flu

Please click here for updated information regarding the Avian (Bird) Flu from the Center of Disease Control (CDC).