The Disease

Influenza, known more commonly as "the flu," is caused by the influenza virus, which infects the respiratory tract (nose, throat, and lungs). Unlike many other viral respiratory infections, such as the common cold, the flu can cause severe illness and life threatening complications in many people.

Influenza is a respiratory illness. Symptoms of flu include fever, headache, extreme tiredness, dry cough, sore throat, runny or stuffy nose, and muscle aches. Children can have additional gastrointestinal symptoms, such as nausea, vomiting, and diarrhea, but these symptoms are uncommon in adults. Although the term "stomach flu" is sometimes used to describe vomiting, nausea, or diarrhea, these illnesses are caused by other viruses, bacteria, or possibly parasites, and are rarely related to influenza.

The flu season in the United States can occur anytime between late December and March. The most common way that influenza viruses are spread is by one person directly inhaling the infected respiratory droplets of a sick person's coughs and sneezes. Though much less frequent, the viruses can also be spread by touch: when a person touches infected respiratory droplets on another person or an object and then touches their own mouth or nose (or someone else's mouth or nose) before washing their hands.

Each flu season is unique, but it is estimated that approximately 10% to 20% of US residents get the flu, and an average of 114,000 persons are hospitalized for flu-related complications. About 36,000 Americans on average die per year from the complications of flu.

Content derived from the Centers for Disease Control and Prevention, NationalCenter for Immunization and Respiratory Diseases
and American Academy of Pediatrics Policy