Influenza

Overview

Influenza or "flu" is a common infection of the respiratory tract. It is highly contagious and is spread from person to person through coughing and sneezing. It is most prevalent from November through April and strikes between 10% and 25% of Canadians annually. The flu affects people of all ages and causes moderate to severe illness. However as many as 1500 Canadians mainly seniors die of flu complications each year.

Cause

The flu is caused by a virus called the influenza virus. There are three types of influenza viruses influenza A B and C. Influenza A can infect humans and other animals while influenza B and C infect only humans. Influenza C virus causes a very mild illness and does not cause epidemics.

The influenza virus spreads through droplets that have been coughed or sneezed into the air by someone who has the flu. You can get the flu by breathing in these droplets through your nose or mouth or by the droplets landing directly on your eyes. The flu virus is also found on the hands of people with the flu and on surfaces they have touched. You can become infected if you shake hands with infected persons or touch contaminated surfaces and transfer the virus to your own eyes nose or mouth.

Symptoms

Many people use the terms "flu" or "stomach flu" to describe other illnesses that may actually be a cold or a mild case of food poisoning. There is no such thing as "stomach flu." A true case of influenza typically starts with a headache chills and cough which are followed rapidly by fever loss of appetite muscle aches and fatigue runny nose sneezing watery eyes and throat irritation. Children may have nausea vomiting and diarrhea but these symptoms are uncommon in adults.

If you have the flu you may have some or all of these symptoms:

  • Fever: usual high fever (102F/39C-104F/40C) sudden onset lasts 3-4 days
  • Headache: usual can be severe
  • Aches and pains: usual often severe
  • Fatigue and weakness: usual severe may last 2-3 weeks or more
  • Extreme fatigue: usual early onset can be severe
  • Runny stuffy nose: common
  • Sneezing: sometimes
  • Sore throat: common
  • Chest discomfort coughing: can become severe

Treatment

If you come down with the flu you can lessen the discomfort by treating the symptoms:

  • Treat fever and muscle aches with aspirin acetaminophen or ibuprofen. Never give aspirin to children under the age of 18 years of age because there is a possibility that they could develop Reyes Syndrome a severe condition of the liver and central nervous system.
  • Drink plenty of fluids to prevent dehydration
  • Rest in bed

There are also some drugs available to treat or even prevent some strains of influenza but they must be taken before or within 48 hours of developing symptoms. Ask your doctor about a prescription.

Most people recover from the flu within a week or ten days. However some are at greater risk for more severe and longer-lasting complications such as pneumonia. The groups at greater risk include very young children people over 65 and people who already have medical conditions such as chronic respiratory disease heart or kidney disease diabetes or a depressed immune system because of cancer HIV infection or some other cause.

Prevention

The best protection from influenza is an annual flu shot. The influenza vaccine is an inactivated (killed) viral vaccine. The strains which are chosen to be included in the vaccine are those which scientists have determined will be the predominant strains during the current influenza season. After you get a flu shot your immune system produces antibodies against the strains of virus in the vaccine. The antibodies are effective for four to six months. When you are exposed to the influenza virus the antibodies will help to prevent infection or reduce the severity of the illness.

The effectiveness of the vaccine in a particular year depends on how well the strains used to make the vaccine "match" the strains that are causing illness. When the match is a good one the vaccine can prevent symptoms of influenza in 70% to 90% of healthy young adults. While its effectiveness is lower in the elderly the flu vaccine has been shown to significantly protect against severe complications hospitalizations and death.

To be effective it is important that you get your annual flu shot early preferably in October or November. Only one shot is needed for older children and adults. Previously unvaccinated children under the age of nine require two doses given one month apart.

Certain groups should not be vaccinated. These include children under the age of six months and people who have had a severe allergic reaction to eggs or a previous dose of the vaccine. If in doubt check with your doctor.

Side effects

The flu shot cannot cause influenza because the vaccine does not contain live virus. There can however be minor side effects. Soreness at the injection site lasting up to two days is common. Fever discomfort and muscle pain may occur six to 12 hours after vaccination and last a day or so.

You might also notice fever fatigue and muscle aches within six to 12 hours after your shot. This may last a day or two. Some people develop a condition called "oculo-respiratory syndrome" after a flu shot. The symptoms include red eyes and respiratory effects such as cough wheezing chest tightness difficulty breathing or sore throat. In most cases the symptoms are mild and disappear within 48 hours.

Severe allergic reactions to flu shots are rare. A rare but possible side effect of influenza vaccination is Guillain-Barré syndrome (GBS). This is an autoimmune disease that attacks the nervous system and results in weakness and abnormal sensations. But most patients recover fully. Your chance of developing GBS as a result of a flu shot is one in a million.

For more information on influenza contact your local public health department or your health care provider. Or contact:

Public Health Agency of Canada's Immunization and Respiratory Infections Division

Also visit the following Web sites: