What Is the Flu?

Worried about catching the flu? Want to learn some ways to prevent it? Then read on to learn more about influenza — what it is, how it’s spread, and who’s at greatest risk for getting it. Knowledge is power when it comes to preventing flu!

What is the flu?

Influenza, commonly known as the “flu,” is an extremely contagious respiratory illness caused by influenza A or B viruses. Flu appears most frequently in winter and early spring. The flu virus attacks the body by spreading through the upper and/or lower respiratory tract.

What’s the difference between a cold and flu?

The common cold and flu are both contagious viral infections of the respiratory tract. Although the symptoms can be similar, flu is much worse. A cold may drag you down a bit, but the flu can make you shudder at the very thought of getting out of bed.

Congestion, sore throat, and sneezing are common with colds. Both cold and flu may bring coughing (less common), headache, and chest discomfort. With the flu, though, you are likely to run a high fever for several days and have body aches, fatigue, and weakness. Symptoms of the flu also tend to come on abruptly. Usually, complications from colds are relatively minor, but a case of flu can lead to a life-threatening illness such as pneumonia.

More than 100 types of cold viruses are known, and new strains of flu evolve every few years. Since both diseases are viral, antibiotics cannot conquer cold or flu. Remember: Antibiotics only treat bacterial infections.

Four antiviral medications are available to treat flu. But there are no medications that specifically defeat the common cold. Antibiotics may be helpful only if there is a secondary bacterial infection.

For in-depth information, see WebMD’s Flu Treatment.

How are stomach flu and influenza different?

“Stomach flu” is a popular term, but not a true medical diagnosis. It’s not uncommon to mistake gastroenteritis, which is what stomach flu is, for the viral infection we commonly call the “flu.” Gastroenteritis refers to inflammation of the gastrointestinal tract (stomach and intestines). Viruses are the most common cause of stomach flu. With gastroenteritis, you may have symptoms such as fever, abdominal cramps, nausea, vomiting, and diarrhea.

For more about gastrointestinal flu, read WebMD’s Stomach Flu or Influenza?

How is flu spread?

The flu virus is spread from person to person through respiratory secretions and typically sweeps through large groups of people who spend time in close contact, such as in daycare facilities, classrooms, college dormitories, military barracks, offices, and nursing homes.

Flu is spread when you inhale droplets in the air that contain the flu virus, make direct contact with respiratory secretions through sharing drinks or utensils, or handle items contaminated by an infected person. In the latter case, the flu virus on your skin can infect you when you touch or rub your eyes, nose, or mouth. That’s why frequent and thorough handwashing is a key way to limit the spread of influenza. Flu symptoms start to develop from one to four days after infection with the virus.

Who’s at greatest risk for flu complications?

While anyone can get flu, infants, the elderly, pregnant women, and people with chronic ailments such as diabetes, heart disease, lung disease, and HIV are at highest risk for flu complications. Despite advances in flu prevention and treatment, the CDC estimates that deaths related to influenza range from 3,000 to 49,000 deaths in the United States each year.

Specific strains of flu can be prevented by a flu vaccine, either a flu shot or nasal spray flu vaccine. In addition, antiviral medications are available to prevent flu. These drugs may help reduce the severity and the duration of flu and are best used within the first 48 hours of the appearance of flu symptoms.

For in-depth information, see WebMD’s Flu Complications.

Are there different types of flu viruses?

Researchers divide flu viruses into three general categories: types A, B, and C. All three types can mutate, or change into new strains, and type A influenza mutates often, yielding new strains of the virus every few years. This means that you can never develop a permanent immunity to influenza. Even if you develop antibodies against a flu virus one year, those antibodies are unlikely to protect you against a new strain of the flu virus the next year.

Type A mutations are responsible for major flu epidemics every few years and for the major pandemics that can occur, though rarely. Type B is less common and generally results in milder cases of flu. However, major flu epidemics can occur with type B every three to five years.

Type C causes infection but does not cause typical flu symptoms. Both influenza A and B have been linked to the development of Reye’s syndrome, a potentially fatal complication that usually affects children and teens under age 18. Widespread outbreaks of Reye’s syndrome have occurred with influenza type B and also with chickenpox, but other viruses have been implicated. The risk of Reye’s syndrome is increased when taking aspirin, so  anyone under age 18 should not take aspirin if they have any viral symptoms or are recovering from the flu or any other virus.

Most influenza viruses that infect humans seem to originate in parts of Asia, where close contact between livestock and people creates a hospitable environment for mutation and transmission of viruses. Swine, or pigs, can catch both avian (meaning from birds, such as poultry) and human forms of a virus and act as hosts for these different viral strains to meet and mutate into new forms. The swine then transmit the new form of the virus to people in the same way in which people infect each other — by transmitting viruses through droplets in the air that people breathe in.

For in-depth information, see WebMD’s Types of Flu.

What is avian or bird flu?

Bird flu, or avian influenza, is an infectious disease of birds caused by type A strains of the influenza virus. Bird flu epidemics have occurred worldwide.

Bird flu is a leading contender to be the next pandemic flu bug because it has caused an unprecedented epidemic in poultry and wild birds across Asia and Eastern Europe. Still, no one knows for sure whether this will cause the next human flu pandemic.

For in-depth information, see WebMD’s Understanding Avian or Bird Flu.