Health Library

Influenza

Definition

The flu (also called influenza) is a viral infection. It affects the respiratory system. It can cause mild-to-severe illness, and sometimes it can lead to death.

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The best way to avoid getting the flu is by being vaccinated every year.

Causes

The influenza virus causes the flu. Each winter, the virus spreads around the world. The strains are usually different from one year to the next. While less likely, it is possible to get the flu when it is not flu season.

The two main kinds of influenza virus are Type A and Type B.

Someone infected with the virus may sneeze or cough. This releases droplets into the air. If you breathe in infected droplets, you can become infected. You can also become infected through touch. If you touch a contaminated surface, you may transfer the virus from your hand to your mouth or nose.

Risk Factors

Factors that increase your chance of the flu include:

  • Living or working in crowded conditions (such as, nursing homes, schools, military forces, daycare centers)
  • Being physically or mentally disabled—people with disabilities may not be able to easily communicate their symptoms or may have trouble practicing preventive measures against the flu, putting them more at risk.

Certain groups of people are at a higher risk of developing complications from the flu. Risk factors for complications include:

  • Children younger than five years old
  • Being 65 years old and older
  • Having certain conditions, including chronic lung condition (such as asthma ); cardiovascular disease; kidney, liver, neurological, blood, or metabolic condition (such as diabetes)
  • Having a suppressed immune system (such as HIV )
  • Being pregnant during the flu season
  • Being younger than 18 years old and receiving long-term aspirin therapy (may be at risk for Reye syndrome)
  • Living in nursing homes or other long-term care facilities
  • Being American Indian/Alaska Native
  • Being severely obese

Symptoms

If you have the flu, you might infect others one day before symptoms start and up to five days (sometimes more) after you become sick. This means you may be infecting others even before you know you are sick.

Symptoms usually start abruptly. They may include:

  • High fever and chills
  • Severe muscle aches
  • Severe fatigue
  • Headache
  • Decreased appetite or other gastrointestinal symptoms like nausea, vomiting, and diarrhea (more common in children than adults)
  • Runny nose, nasal congestion
  • Sneezing
  • Watery eyes, conjunctivitis
  • Sore throat
  • Cough (can last for two or more weeks)
  • Swollen lymph nodes in the neck

You may start to feel better in 7-10 days. However, you may still have a cough and feel tired.

Diagnosis

The doctor will ask about your symptoms and medical history. Diagnosis of the flu is usually based on symptoms.

In some cases, your doctor may take samples from your nose or throat to confirm the diagnosis.

Treatment

Treatment may include:

Antiviral Prescription Medicines

Most people with the flu do not need antiviral medicine. Check with your doctor. You may need the medicine if you are in a high-risk group or if you have a severe illness (for example, breathing problems).

Antiviral medicines generally may help relieve symptoms and shorten the time you are sick. They must be taken within 48 hours of the first symptoms. Examples of these medicines include:

  • Zanamivir (Relenza)—may worsen asthma or chronic obstructive pulmonary disease (COPD)
  • Oseltamivir (Tamiflu)—may increase the risk of self-injury and confusion shortly after taking, especially in children
    • Note: Children should be closely monitored for signs of unusual behavior while taking this medicine. (Zanamivir may also cause these side effects.)
  • Amantadine (Symmetrel)
  • Rimantadine (Flumadine)

Some strains of the seasonal influenza virus are resistant to these medicines.

Rest

It is important to get plenty of rest when your body is fighting the flu.

Fluids

Drink a lot of liquids. This can include water, juice, and caffeine-free tea.

Over-the-Counter Pain Relievers

These medicines are used to control fever and to treat aches and pains. Adults can use:

  • Acetaminophen
  • Ibuprofen

Decongestants

Decongestants are available as pills or nasal sprays. If you use a nasal spray, do not use it longer than 3-5 days. You may experience an increase in congestion when you stop using the spray. This is called rebound effect.

Cough Medicines

These include:

  • Over-the-counter (OTC) cough and cold medicines, including decongestants, expectorants, antihistamines, and cough suppressants
    • OTC cough and cold products should not be used to treat infants or children less than two years old. Rare but serious side effects have been reported. They include death, convulsions, rapid heart rates, and decreased levels of consciousness. Serious side effects have also been reported in children aged 2-11 years. Research is still going on for the safety of OTC products for this age group.
  • Prescription cough medicines
  • Cough drops

Herbal Treatment

Elderberry extract may reduce flu symptoms. Researchers found that products containing elderberry, like Sambucol and ViraBLOC, decreased symptoms in some studies. However, be aware that the government does not regulate herbal remedies. Therefore, the herbal supplements that you buy may not have the same ingredients as those studied and they may contain impurities (things that should not be in the product).

If you are diagnosed with the flu, follow your doctor's instructions.

Prevention

Ways to Avoid Getting the Flu

The best way to prevent getting the flu is to be vaccinated. You will need to be vaccinated each year since the virus may change every season. Two forms of the vaccine are available:

  • Flu shot (injection)—all people aged six months and older should get the flu shot. Note: Children eight years and younger may need two shots.
  • Nasal spray—the spray is approved for healthy, nonpregnant people aged 2-49 years old. Note: Certain people, like those who care for others with weakened immune systems, should get the flu shot instead of the nasal spray.

For the best protection, get vaccinated as soon as the vaccine is available in your area (vaccinations are offered throughout the flu season, which may begin in October).

It takes about two weeks for the vaccine to protect you against the flu.

People Who Should Not Be Vaccinated

There are people who should not be vaccinated, such as:

  • Children less than six months old
  • Those who are severely allergic to eggs
  • Those who had a severe reaction to vaccination in the past
  • Those who have a history of Guillain-Barré Syndrome
  • Those who are very sick and have a fever—talk to your doctor before being vaccinated.
General Measures to Reduce Your Risk

There are general measures you can take to reduce your risk of getting the flu:

  • Wash your hands often, especially when you come in contact with someone who is sick. Wash your hands for 15-20 seconds with soap and water. Rubbing alcohol-based cleaners on your hands is also helpful.
  • Avoid close contact with people who have respiratory infections. The flu can spread starting one day before and ending seven days after symptoms appear. If have to be in close contact with a sick person, wear a face mask or a disposable respirator.
  • Cover your mouth and nose with a tissue when you cough or sneeze. Throw away the tissue after you use it. Coughing or sneezing into your elbow or upper sleeve is also helpful.
  • Do not spit.
  • Do not share drinks or personal items.
  • Do not bite your nails or put your hands near your eyes, mouth, or nose.
  • Keep surfaces clean by wiping them with a household disinfectant.
Antiviral Medications

Sometimes it is beneficial to take antiviral medicines to prevent the flu. You may want to talk to your doctor about taking these medicines to lower your risk of getting the flu if you:

  • Are exposed to the flu, and
  • Are at high risk for complications
  • Are a healthcare worker, public health worker, or first responder

If you have the flu and live with someone who is at risk for complications (such as, elderly, babies, someone with cancer), that person may need to take antiviral medicines to prevent getting the flu from you.

Remember that these medicines are not a substitute for being vaccinated. Vaccination is still the best way to prevent the flu.

Ways to Avoid Spreading the Flu

If you have the flu, take these steps to avoid spreading it to others:

  • Avoid close contact with people. Before you can return to school or work, your fever should be gone for at least 24 hours without the help of fever-reducing medicine. This could take up to seven days after symptoms first appear. It is important to stay home if you have the flu, leaving your house only to see your doctor.
  • If you cannot avoid close contact, cover your mouth and nose with a face mask.
  • Wash your hands for 15-20 seconds with soap and water. Even if someone in your house has the flu, you may be able to avoid getting sick by washing your hands. Using a hand sanitizer is also helpful.
  • Cover your mouth and nose with a tissue when you cough or sneeze. Throw away the tissue after you use it. Coughing or sneezing into your elbow or upper sleeve will also keep you from spreading the flu with your hands. Do not spit.
  • Do not share drinks or personal items.
  • Wash eating utensils with hot water and soap.
  • Do not bite your nails or put your hands near your eyes, mouth, or nose.
  • Keep surfaces clean by wiping them with a household disinfectant.
  • Use the hot setting on your washing machine when washing infected laundry.

Resources

American Lung Association
http://www.lung.org
Centers for Disease Control and Prevention
http://www.cdc.gov/flu

Canadian Resources

Public Health Agency of Canada
http://www.phac-aspc.gc.ca

References

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