What is influenza (flu)?
Influenza, or 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 ill. Although most people are ill with the flu for only a few days, some have a much more serious illness and may need to go to the hospital. The flu can also lead to pneumonia and death.
The flu viruses continually change (mutate).Currently, three different influenza viruses circulate worldwide. Vaccines given each year to protect against the flu fight 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, telephone receivers, and eating or drinking 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 the whole body seems to suffer. People usually become very ill with several, or all, of the following symptoms:
- High fever
- Runny or stuffy nose
- Sneezing at times
- Cough, often becoming severe
- Severe aches and pains
- Fatigue for several weeks
- Sometimes a sore throat
- Extreme exhaustion
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 conditions. Always consult your health care 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.
How is the flu treated?
Specific treatment for the flu will be determined by your health care provider based on:
- Your age, overall health, and medical history
- Extent and type of influenza, and severity of symptoms
- How long you've had symptoms
- Your tolerance for specific medications, procedures, or therapies
- Expectations for the course of the disease
- Your opinion or preference
The goal of treatment for the flu is to help prevent or decrease the severity of symptoms. Treatment may include:
- Medications to relieve aches and fever. Do not give aspirin to children with fever. The drug of choice for children is acetaminophen (such as Tylenol).
- Medications for congestion and nasal discharge
- Bed rest and increased intake of fluids
- Antiviral medications. When started within the first 2 days of the illness, they can reduce how long you'll have the flu, but they can't cure it. These medications do have some side effects, such as nervousness, lightheadedness, or nausea. These medications are prescribed by a doctor.
Consult your health care provider for more information.
What are the complications of the flu?
The most common complication of the flu is pneumonia. It can also cause serious muscle and central nervous system complications. Of those who get the flu, between 3,000 and 49,000 will die from it or from complications. Most of these deaths occur in people over 65.
Can the flu be prevented?
A new flu vaccine is made each fall. Everyone 6 months and older should get a flu vaccine each season It is usually recommended for specific groups of people, as well as for anyone who wants to avoid having the flu.
The flu vaccine is safe. The CDC and the FDA closely watch vaccine safety, and hundreds of millions of flu vaccines have been safely given across the country for decades.
The flu vaccine can't give you the flu. The most common side effects from a flu shot are soreness where the shot was given and maybe a low fever or achiness. The nasal spray flu vaccine might cause congestion, runny nose, sore throat, or cough. If you do have them at all, these side effects are usually mild and short-lived.
The effectiveness of the vaccine varies from one person to another, depending on factors such as age and overall health.
A nasal spray flu vaccine is currently approved to prevent flu in healthy children and teens ages 2 to 17, and healthy adults ages 18 to 49. As with other live virus vaccines, the nasal spray vaccine should not be given for any reason to pregnant women or people with weak immune systems. This includes those with immune deficiency diseases, such as AIDS or cancer, or people who are being treated with medications that weaken the immune system. The nasal spray vaccine also should not be given to these groups of people:
- Children younger than 2 years old
- Any person with asthma
- Children younger than 5 years who have wheezing
- Adults ages 50 and older
- Children and adolescents who are taking aspirin as long-term treatment
- Children and adults who have a chronic disorder of the lung, heart, kidney, liver, nerves, blood, or metabolism
Following these precautions may also be helpful:
- When possible, avoid or limit contact with infected people.
- Frequent handwashing may reduce, but not eliminate, the risk of infection.
- A person who is coughing or sneezing should cover his or her nose and mouth with a handkerchief to limit spread of the virus.
The flu causes complications that may develop into a more serious disease or become dangerous to some groups, such as older adults and those with chronic medical conditions. For these reasons, the CDC recommends that the following groups get a vaccine each year. Always consult your health care provider for more information regarding who should receive the flu vaccine:
- People ages 50 and older. Vaccine effectiveness may be lower for older adults, but it can significantly reduce their chances of serious illness or death from the flu.
- Children and teens 6 months to 19 years old
- Residents of nursing homes and any other chronic care facilities that house people of any age who have chronic medical conditions
- Adults and children who have chronic disorders of the lungs or heart, including children with asthma
- Adults and children who have these medical conditions:
- Chronic metabolic diseases, such as diabetes
- Kidney dysfunction
- Weak immune system
- Blood disorders, such as sickle cell disease
- Children and teens ages 6 months to 19 years who take aspirin as long-term therapy
- Women who will be pregnant during flu season
- Health care providers
- Employees of nursing homes and chronic care facilities who have contact with patients or residents
- Providers of home care to people at high risk
- Household members, including children, of people high-risk groups
- People of any age who wish to lower their chances of getting the flu
Although the flu immunization is safe, some people should NOT be vaccinated. These include:
- People who are allergic to eggs may be told not to get the vaccine
- People who have had a severe reaction in the past after getting the flu vaccination
- People who are sick with a fever (these people should get vaccinated after they have recovered)
- Babies who are 6 months old or younger
- People who have a history of Guillain-Barré syndrome, a severe paralyzing illness, after getting the flu vaccination
The CDC recommends getting the flu shot every year, as soon as it becomes available in your community. Flu season can begin as early as October and most commonly peaks in the U.S. in January or February, but flu seasons are unpredictable. The flu shot takes 1 to 2 weeks to become effective.
The CDC recommends that travelers have the flu vaccine at least 2 weeks before planned travel to allow time to develop immunity. Consult your doctor for more information.
When should I call my health care provider?
For most people, the flu can be treated at home without treatment from your health care provider. However, if your condition or situation makes you more susceptible to complications from the flu, tell your health care provider when you suspect you have the flu. If your symptoms get worse or you have new symptoms, let your health care provider know.
Key points about the flu
- The flu is an easily spread viral respiratory tract infection.
- The flu is caused by viruses that are generally passed from person to person through the air.
- The flu is treated with bedrest, increased fluid intake, and medications to treat discomfort and fever
- Antiviral medications taken within the first 2 days of illness can reduce the length and severity of the disease but does not cure it.
- The flu vaccination received every year is the best prevention.
Tips to help you get the most from a visit to your health care provider:
- Before your visit, write down questions you want answered.
- Bring someone with you to help you ask questions and remember what your provider tells you.
- At the visit, write down the names of new medicines, treatments, or tests, and any new instructions your provider gives you.
- If you have a follow-up appointment, write down the date, time, and purpose for that visit.
- Know how you can contact your provider if you have questions.
Online Medical Reviewer:
Foster, Sara, RN, MPH
Online Medical Reviewer:
Holloway, Beth, RN, M.Ed.
Online Medical Reviewer:
newMentor board-certified, academically affiliated clinician
Online Medical Reviewer:
Trevino, Heather M, BSN, RNC
Date Last Reviewed:
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