Flu (Influenza)

What Is It?

Flu, known medically as influenza, is a respiratory infection caused by the influenza virus. The infection typically is spread by air or by direct contact from one person to another. Most cases occur during epidemics, which peak during the winter months nearly every year. Influenza virus is very contagious. A particularly widespread and severe epidemic is called a pandemic.

Compared with other viruses, influenza can strike remarkably large numbers of people in a relatively short time. Each year, about 25 million people seek medical care for the symptoms of flu during flu season. In the United States, the Asian flu of 1957-1958 caused 70,000 deaths, and the Hong Kong flu of 1968-1969 killed 34,000 people. In the worst recorded pandemic of influenza, the 1918-1919 Spanish flu, 20 to 40 million people throughout the world died in less than one year.

The most common types of influenza virus are A and B. Influenza A is the one usually responsible for the annual epidemics. Most people get multiple flu infections during their lives. With many other types of infections for example, mumps having the disease once protects against a second infection because the body's immune system "remembers" the returning virus, attacks it immediately and rapidly eliminates it. With influenza, the virus usually has mutated (changed) somewhat since the first infection, and the change is enough to fool your immune system. Instead of attacking the virus rapidly, as it would a virus that it had seen before, the immune system responds slowly. By the time the immune response is in full gear, millions of the body's cells already have been infected with the virus.

Symptoms

Flu can cause a variety of symptoms. They can be mild or severe depending on the type of virus and your age and overall health. Although it is a respiratory virus, flu can affect other body systems, making you feel sick all over. Symptoms can include any or all of the following:

• Chills
• Moderate to high fever (101° to 103° Fahrenheit)
• Sore throat
• Runny nose
• Muscle aches
• Headaches
• Fatigue
• Cough
• Diarrhea
• Dizziness

Dangerous complications also can develop from flu. One of the most feared complications, a bacterial "superinfection," occurs when the influenza virus attacks a lung and weakens its defenses, allowing bacteria that normally live quietly in the nose and throat to descend into the lung and cause bacterial pneumonia. People older than 50, infants, and those with certain chronic diseases or suppressed immune systems are especially vulnerable to complications.

Diagnosis

Your doctor will evaluate your symptoms to determine whether you have flu or a cold. If you are sneezing and have a stuffy nose, you may have a cold. Flu is more likely to cause fever, coughing, chills and muscle aches. It also is more seasonal than colds. Flu tends to occur during winter months, whereas colds occur all year long.

Most of the time, doctors assume the diagnosis is flu when you have symptoms of influenza in the winter. If your symptoms or findings on physical examination suggest something other then the flu, your doctor may order blood tests and swab your nose and throat to send secretions to the laboratory for specific influenza testing. Your doctor may order a chest X-ray if he or she suspects that the influenza virus has caused a lung infection (pneumonia) or may lead to a bacterial superinfection.

Expected Duration

Influenza symptoms can last for as few as 24 hours or for a week or more. A typical case lasts four or five days. As long as you have symptoms, you are contagious and can spread the infection to others.

Prevention

Options for heading off an attack of influenza have increased steadily in recent years.

• Vaccination People who are at a high risk of infection with influenza, such as health care workers, or those who are more likely to get complications if infected should get vaccinated against the disease every year. Each year's flu vaccine is different because it is adjusted to combat whatever virus strains are expected to be circulating that season. The vaccine is particularly recommended for:
  • Children aged 6 to 23 months
  • Children or teenagers who are receiving long-term aspirin therapy
  • Pregnant women who will be in the second or third trimester during flu season
  • Adults aged 50 or older, even if in good health
  • Adults or children who have certain chronic illnesses, especially those of the heart, lung or kidneys; diabetes; or severe forms of anemia
  • Adults or children who have illnesses or who take medications that reduce or suppress immune defenses
  • Adults who live in nursing homes or assisted-living centers
  • Health care professionals and others who are in close contact with anyone in the above high-risk groups
  There is growing support for a policy to recommend the flu vaccine to all adults, and many doctors will give the vaccine to any adult who requests it. The standard flu vaccine is 70% to 90% effective in helping healthy people younger than 65 to avoid the disease or lessen its severity. For maximum effectiveness, doctors advise people to get vaccinated in October or November, the start of flu season. Healthy people between the ages of 5 and 49 have an alternative to the flu shot. FluMist is an intranasal vaccine spray that appears to offer similar protection. It uses a deactivated live virus rather than the killed virus in the shot. FluMist is not any more effective than the standard flu shot. Because FluMist is so new, people at the highest risk for flu (people older than 49 and those with chronic health conditions) should receive the injected vaccine.
• Good hygiene The virus usually is passed through the air, by coughing. It also is passed by direct contact, such as shaking hands or kissing. For this reason, practicing good hygiene covering your mouth when you cough and washing your hands frequently can help you to avoid getting the flu or spreading it to others.
• Antiviral drugs Two older antiviral drugs amantadine (Symmetrel) and rimantadine (Flumadine) and two newer ones zanamivir (Relenza) and oseltamivir (Tamiflu) can reduce your chance of getting the flu by 70% to 90% if they are taken just before an expected outbreak. Zanamivir is a spray that is inhaled through the mouth. The others are pills. The older drugs, particularly amantadine, tend to have more side effects than the newer drugs. The side effects include nausea, vomiting, irritability, depression and difficulty sleeping. Zanamivir generally should be avoided in people who have asthma or chronic lung disease because since it may worsen wheezing. The two older drugs are effective only against the influenza type A virus, whereas the newer drugs also treat type B. The newer drugs are much more expensive.

Treatment

To ease symptoms, your doctor will recommend that you rest and drink plenty of fluids (at least eight cups daily). For fever and body aches, you can take over-the-counter pain relievers. If any of the four antiviral drugs mentioned in the Prevention section above are taken within 48 hours of the start of symptoms, they may speed recovery by about one day. Because flu is a viral infection, antibiotics are not effective. Children who are suspected of having flu, and who have high fevers should never be given aspirin to treat the fever. This can cause the disease called Reye's syndrome. Instead, acetaminophen (Tylenol) should be used.

When To Call A Professional

If you have a chronic disease and suddenly get flu symptoms, you should call your doctor's office, because you may benefit from starting an antiviral medication within 48 hours. You also should notify your doctor if you have flulike symptoms along with chest pain, ear pain, shortness of breath, fever that does not go away or a cough that produces blood or thick, foul-smelling mucus.

Prognosis

Although most people recover fully from the flu, some develop serious complications, including life-threatening conditions such as pneumonia. About 20,000 people in the United States die of flu complications each year, and thousands more need to be hospitalized prior to recovery.

Additional Info

Centers for Disease Control and Prevention (CDC)

1600 Clifton Road

Atlanta, GA 30333

Phone: 404-639-3534

Toll-Free: 1-800-311-3435

http://www.cdc.gov/