Influenza: The Disease

The Flu Season

In the Northern hemisphere, winter is the time for flu. In the United States, the flu season can range from November through March, and even past March in some years. During the past 21 flu seasons, months with the heaviest flu activity (peak months) occurred in December in 4 years, January in 5 years, February in 9 years, and March in 3 years.

Peak Months for Flu Activity Over the Past 21 Years

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 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.

Do I have the flu?

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.

Do not give aspirin to a child or teenager who has the flu.

Never give aspirin to children or teenagers who have flu-like symptoms – and particularly fever – without first speaking to your doctor. Giving aspirin to children and teenagers who have influenza can cause a rare but serious illness called Reye syndrome. Children or teenagers with the flu should get plenty of rest, drink lots of liquids, and take medicines that contain no aspirin to relieve symptoms.

The Myth of the "Stomach Flu"

Many people use the term "stomach flu" to describe illnesses with nausea, vomiting, or diarrhea. These symptoms can be caused by many different viruses, bacteria, or even parasites. While vomiting, diarrhea, and being nauseous or "sick to your stomach" can sometimes be related to the flu – particularly in children – these problems are rarely the main symptoms of influenza. The flu is a respiratory disease and not a stomach or intestinal disease.

About Flu

Influenza (commonly called “the flu”) is a contagious respiratory illness caused by influenza viruses. Infection with influenza viruses can result in severe illness and life-threatening complications. An estimated 10% to 20% of U.S. residents get the flu each year: an average of 114,000 people are hospitalized for flu-related complications and 36,000 Americans die each year from complications of flu.

Symptoms of Flu

Symptoms of flu include fever (usually high), headache, extreme tiredness, dry cough, sore throat, runny or stuffy nose, and muscle aches. Gastro-intestinal symptoms, such as nausea, vomiting, and diarrhea, are much more common among children than adults.

Spread of Flu

Influenza viruses are spread when a person who has the flu coughs, sneezes, or speaks and spreads virus into the air, and other people inhale the virus. When these viruses enter the nose, throat, or lungs of a person, they begin to multiply, causing symptoms of the flu. The viruses can also be spread when a person touches a surface with flu viruses on it (for example, a door handle) and then touches his or her nose or mouth.

A person who is sick with the flu can spread viruses – that means they are contagious. Adults may be contagious from 1 day before developing symptoms to up to 7 days after getting sick. Children can be contagious for longer than 7 days.

Preventing Flu

Vaccination: The single best way to prevent the flu is to get vaccinated each fall. In the absence of vaccine, however, there are other ways to protect against flu.

Antiviral Medications: Three antiviral drugs (amantadine, rimantadine, and oseltamivir) are approved and commercially available for use in preventing flu. All of these medications are prescription drugs, and a doctor should be consulted before the drugs are used for preventing the flu.

Other Habits for Good Health

The following steps may help prevent the spread of respiratory illnesses like flu:

Avoid close contact
Avoid close contact with people who are sick. When you are sick, keep your distance from others to protect them from getting sick too.

Stay home when you are sick
If possible, stay home from work, school, and errands when you are sick. You will help prevent others from catching your illness.

Cover your mouth and nose
Cover your mouth and nose with a tissue when coughing or sneezing. It may prevent those around you from getting sick.

Clean your hands
Washing your hands often will help protect you from germs.

Avoid touching your eyes, nose or mouth
Germs are often spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose, or mouth.

Diagnosing the Flu

Tests are available that can determine if you have the flu as long as you are tested within the first 2 or 3 days after your symptoms begin. In addition, a doctor's examination may be needed to determine whether a person has another infection that is a complication of the flu.

At Special Risk of Complications From Flu

Certain people are at increased risk for serious complications from the flu. This group includes people age 65 years and older and people of any age with chronic medical conditions. Pregnant women and children between 6 months and 23 months of age also are at increased risk from flu complications.

Complications from Flu

Some of the complications caused by flu include bacterial pneumonia, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes. Children may get sinus problems and ear infections.

Treating the Flu

Antiviral Medications: Four antiviral drugs (amantadine, rimantadine, zanamavir and oseltamivir) have been approved for treatment of the flu. All of these must be prescribed by a doctor. Antiviral treatment lasts for 5 days and must be started within the first 2 days of illness.

What to Do if You Get Sick this Flu Season

If you develop the flu, it is advisable to get plenty of rest, drink a lot of liquids, and avoid using alcohol and tobacco. Also, you can take medications to relieve the symptoms of flu (but never give aspirin to children or teenagers who have flu-like symptoms – and particularly fever – without first speaking to your doctor.)

If, however, your flu symptoms are unusually severe (for example, if you are having trouble breathing), you should consult your health-care provider right away.

If you are at special risk from complications of flu, you should consult your health-care provider when your flu symptoms begin. This includes people 65 years or older, people with chronic medical conditions, pregnant women, or children. Your doctor may choose to use certain antiviral drugs to treat the flu.

Information provided by the Centers for Disease Control and Prevention

For more information, visit www.cdc.gov/flu, or call the National Immunization Hotline at (800) 232-2522 (English), (800) 232-0233 (español), or (800) 243-7889 (TTY).