Diseases & Conditions

Influenza (flu)

Influenza is a viral infection that attacks the respiratory system, including your nose, throat, bronchial tubes and lungs. Influenza, commonly called the flu, is not the same as the stomach viruses that cause diarrhea and vomiting.

Anyone can get the flu, but young children, older adults, people with weakened immune systems and those with chronic illnesses are especially vulnerable. If you're at high risk of flu, your first line of defense is an annual flu shot.

Approximately 50 million people died worldwide in the 1918 influenza pandemic. Today, according to the Centers for Disease Control and Prevention, as many as 36,000 people in the United States die each year of complications of influenza and more than 200,000 are hospitalized.

Initially, the flu may seem like a common cold with a runny nose, sneezing and sore throat. But colds usually develop slowly, whereas the flu tends to come on suddenly. And although a cold can be a nuisance, you usually feel much worse with the flu.

Common signs and symptoms of the flu include:

• Fever over 101 F (38 C) in adults, and often as high as 103 to 105 F (39.5 C to 40.5 C) in children
• Chills and sweats
• Headache
• Dry cough
• Muscular aches and pains, especially in your back, arms and legs
• Fatigue and weakness
• Nasal congestion
• Loss of appetite
• Diarrhea and vomiting in children

When to see a doctor
If you have flu symptoms and are at risk of complications, see your doctor right away. Taking antiviral drugs within the first 48 hours after you first notice symptoms may reduce the length of your illness by a day or two and may help prevent more serious problems. Seek immediate medical care if you have signs and symptoms of pneumonia. These include a severe cough that brings up phlegm, a high fever and a sharp pain when you breathe deeply. If you have bacterial pneumonia, you'll need treatment with antibiotics.

Flu viruses travel through the air in droplets when someone with the infection coughs, sneezes or talks. You can inhale the droplets directly, or you can pick up the germs from an object, such as a telephone or computer keyboard, and then transfer them to your eyes, nose or mouth.

The flu is caused by three types (strains) of viruses — influenza A, B and C. Type A can be responsible for the deadly influenza pandemics (worldwide epidemics) that strike every 10 to 40 years. Type B can lead to smaller, more localized outbreaks. And either types A or B can cause the flu that circulates almost every winter. Type C has never been connected with a large epidemic.

Type C is a fairly stable virus, but types A and B are constantly changing, with new strains appearing regularly. Once you've had the flu, you develop antibodies to the strain that caused it, but those antibodies won't protect you from new strains. That's why doctors recommend getting a flu shot every year.

If you're young and healthy, influenza usually isn't serious. Although you may feel miserable while you have it, the flu usually goes away with no lasting effects. But high-risk children and adults may develop complications such as:

• Ear infections
• Acute sinusitis
• Bronchitis
• Pneumonia
• Encephalitis

Of these, pneumococcal pneumonia, a serious bacterial infection of the lungs, is the most common and most serious. For older adults and people with a chronic illness, pneumonia can be deadly. The best protection is vaccination against both pneumococcal pneumonia and influenza.

Usually, you'll need nothing more than bed rest and plenty of fluids to treat the flu. But in some cases, your doctor may prescribe an antiviral medication such as oseltamivir (Tamiflu) or zanamivir (Relenza).

These drugs, which treat both influenza A and B, work by deactivating an enzyme the virus needs to grow and spread. If taken soon after you notice symptoms, they may shorten your illness by a day or so. Oseltamivir is an oral medication, but zanamivir is inhaled through a device similar to an asthma inhaler and shouldn't be used by anyone with respiratory conditions, such as asthma and lung disease.

Both medications can cause side effects, including lightheadedness, nausea, vomiting, loss of appetite and trouble breathing. They can also lead to the development of antiviral-resistant viruses.

In November 2006, the Food and Drug Administration (FDA) required the maker of Tamiflu to include a warning that people with the flu, particularly children, may be at increased risk of self-injury and confusion after taking Tamiflu. The FDA recommends that individuals with the flu who take Tamiflu be closely monitored for signs of unusual behavior. Discuss possible side effects with your doctor before starting any antiviral medication.