Clinical Signs, Symptoms, and Complications of Influenza

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About Influenza

Influenza (commonly called "the flu") is a contagious respiratory illness caused by influenza viruses. Infection with influenza viruses can cause severe illness and life-threatening complications. About 5% to 20% of Americans get influenza each year, about 36,000 Americans die from it each year, and more than 200,000 Americans are hospitalized from flu-related complications each year.

Symptoms of Influenza

Symptoms of flu include fever (usually high - 100 degrees F or more), headache, extreme tiredness, dry cough, sore throat, runny or stuffy nose, and muscle aches. Illness usually lasts for 2 to 7 days, but complete recovery may take longer. Most people recover completely, but influenza can sometimes worsen other health problems, which may lead to death.

"Stomach Flu"
Symptoms of the stomach and intestines, like nausea, vomiting, and diarrhea, are rare in adults but are sometimes seen in children. Some people call diarrhea, nausea, or vomiting that lasts for a day or two 'stomach flu', but that illness is very different from true influenza.

Diagnosing Influenza

Influenza is hard to diagnose because there are several other diseases that resemble it. Tests are available that can tell if you have influenza if 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 from influenza.

Complications from Influenza

Some of the complications caused by influenza 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. Complications can be severe and may lead to death.

People at Risk of Complications from Influenza

Certain people are at increased risk for influenza-related complications and severe disease. This includes people 65 years of age and older, people of any age with chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women, and young children.