Influenza (Flu)

What is influenza (flu)?

Influenza (flu) is an easily spread respiratory tract infection. It is caused by a virus. About 5% to 20% of people in the U.S. get the flu each year. The flu usually starts abruptly, with fever, muscle aches, sore throat, and a cough.

The flu can make people of any age sick. Although most people are sick with the flu for only a few days, some have a much more serious illness. They may need to go to the hospital. The flu can also lead to pneumonia and death.

The flu viruses continually change. Currently, three different influenza viruses circulate worldwide. Vaccines given each year to protect against the flu virus strain expected to cause the illness that year.

What causes the flu?

The flu is caused by a virus. Viruses are generally passed from person to person through the air when an infected person sneezes or coughs.

But the virus can also live for a short time on objects like doorknobs, pens, pencils, keyboards, phones, and cups or eating utensils. So you can also get the flu by touching something that has been recently handled by someone infected with the virus and then touching your own mouth, nose, or eyes.

What are the symptoms of the flu?

Each person may experience symptoms differently. The flu is called a respiratory disease, but it can affect your entire body. People usually become very sick with several, or all, of the following symptoms:

  • Cough, often becoming severe
  • Extreme exhaustion
  • Fatigue for several weeks
  • Headache
  • High fever
  • Runny or stuffy nose
  • Severe aches and pains
  • Sneezing at times
  • Sometimes a sore throat
  • Vomiting and diarrhea

Fever and body aches usually last for 3 to 5 days, but cough and fatigue may last for 2 weeks or more.

The symptoms of the flu may look like other medical problems. Always talk your healthcare provider for a diagnosis.

How is the flu diagnosed?

The flu is diagnosed based on your symptoms. Lab tests may be used to confirm the diagnosis, if necessary.