Influenza is a viral infection that attacks your respiratory system â your nose, throat and lungs. Influenza, commonly called the flu, is not the same as stomach "flu" viruses that cause diarrhea and vomiting.
For most people, influenza resolves on its own. But sometimes, influenza and its complications can be deadly. People at higher risk of developing flu complications include:
Your best defense against influenza is to receive an annual vaccination.
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:
Most people who get the flu can treat themselves at home and often don't need 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 and help prevent more-serious problems.
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 â such as a telephone or computer keyboard â and then transfer them to your eyes, nose or mouth.
People with the virus are likely contagious from the day or so before symptoms first appear until about five days after symptoms begin, though sometimes people are contagious for as long as 10 days after symptoms appear. Children and people with weakened immune systems may be contagious for a slightly longer time.
Influenza viruses are constantly changing, with new strains appearing regularly. If you've had influenza in the past, your body has already made antibodies to fight that particular strain of the virus. If future influenza viruses are similar to those you've encountered before, either by having the disease or by vaccination, those antibodies may prevent infection or lessen its severity.
But antibodies against flu viruses you've encountered in the past can't protect you from new influenza subtypes that can be very different immunologically from what you had before.
Your doctor will conduct a physical exam, look for signs and symptoms of influenza, and possibly order a test that detects influenza viruses.
The most commonly used test is called a rapid influenza diagnostics test, which looks for substances (antigens) on a swab sample from the back of the nose or throat. These tests can provide results in 30 minutes or less. However, results vary greatly and are not always accurate. Your doctor may diagnose you with influenza based on symptoms, despite having a negative test result.
More-sensitive flu tests are available in some specialized hospitals and labs.
If you're young and healthy, seasonal influenza usually isn't serious. Although you may feel miserable while you have it, the flu usually goes away in a week or two with no lasting effects. But high-risk children and adults may develop complications such as:
Pneumonia is the most serious complication. For older adults and people with a chronic illness, pneumonia can be deadly.
The Centers for Disease Control and Prevention recommends annual flu vaccination for everyone over the age of 6 months.
Each year's seasonal flu vaccine contains protection from the three or four influenza viruses that are expected to be the most common during that year's flu season. The vaccine is currently available as an injection only. The CDC no longer recommends nasal spray flu vaccinations because during recent flu seasons, the spray has been relatively ineffective.
The influenza vaccine isn't 100 percent effective, so it's also important to take measures such as these to reduce the spread of infection:
If you do come down with the flu, these measures may help ease your symptoms:
Factors that may increase your risk of developing influenza or its complications include: