Canadian Centre for Occupational Health and Safety
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The word "influenza" (or the "flu") refers to a family of highly contagious viruses. These viruses can make you ill by infecting your nose, throat, and lungs. Adults who have the flu will suddenly feel a fever, cough, sore throat, malaise, and general aches.

However, not everyone will be affected in the same way. Children may also have nausea, vomiting, or diarrhea. In very young children, the fever may not appear or it may not be as severe as in adults. Older persons often experience fever and sometimes chills, but these symptoms may not be as severe as in other adult age groups. In a “normal” influenza year, 4,000 Canadians on average die of influenza and its complications each year, and some years the number of deaths may be as high as 8,000.

There is often confusion between the seasonal ("regular") influenza, the "stomach flu" (which is actually not influenza, but is gastroenteritis - an inflammation of the stomach and intestine), and a common cold. The following chart helps to show these differences:

Influenza (Flu) Stomach "Flu" (Gastroenteritis) Cold
  • Sudden onset of:
    • High fever lasting 3-4 days
    • Cough, chest discomfort
    • Headache
    • Muscle aches and pains
    • Extreme exhaustion - usually at the start
    • Fatigue and weakness that may last 2-3 weeks or longer
    • Sore throat
    • Runny, stuffy nose, and sometimes sneezing
  • Symptoms can last 4-10 days and may become severe. A cough and general fatigue may last for several weeks
  • Complications can lead to dehydration, pneumonia and respiratory failure; can worsen a current chronic condition; can be life-threatening.
  • Yearly flu vaccine will help prevent or ease symptoms (but may not protect against a new pandemic influenza virus)
  • Some people are at greater risk of more severe complications such as pneumonia (e.g. those over 65; those with chronic conditions like diabetes and cancer)
  • Stomach cramps
  • Vomiting and diarrhea
  • Usually lasts 24-72 hrs
  • Yearly flu vaccine does not provide protection (because this illness is not actually caused by an influenza virus)
  • Runny or stuffy nose
  • Sneezing
  • Hacking cough
  • Sore throat
  • Fever is rare
  • Headache is uncommon
  • Sometimes can have mild general aches and pains
  • Sometimes mild fatigue
  • Complications can lead to sinus congestion or earache

Adapted from "Had influenza (flu) lately?" poster by BC Ministry of Health and "Is it a cold or the flu?" by Canadian Coalition for Immunization Awareness & Promotion

Contagious Period: People can be infected and able to spread the virus (i.e. be contagious) 24 to 48 hours before they have any symptoms, and for 7 days after the symptoms start. This period of time when you are not yet sick but can spread the virus is why it is difficult to prevent influenza. Children may be contagious for up to 10 days.

How do I get the flu?

Influenza is highly contagious and spreads very quickly between people, especially in crowded situations. When someone with the flu coughs or sneezes, tiny droplets containing the virus go into the air. You can get the flu by breathing in these droplets through your nose or mouth, or by the droplets landing directly on your eyes. When someone coughs/sneezes and then touches an object (like a door knob) or shakes your hand, you can transfer the virus to your hands and then to your own eyes, nose or mouth where the virus can easily enter your body.

Not everybody who comes in contact with influenza virus will become ill, but they may still spread the infection to others (these people are called "carriers").

What is a pandemic?

A pandemic is a worldwide outbreak of a specific disease that spreads easily and rapidly through many countries. It is usually a serious illness that causes a large percentage of the population to become ill because they have little or no immunity to it.

What is a pandemic flu?

In the case of a flu pandemic, traditionally three or four times a century, the “normal” influenza type “A” virus changes drastically and essentially a new virus appears. Because this virus is radically different, people's immune systems are not able to fight it effectively. It can thus spread quickly and make many people ill and is thus called a pandemic flu. Everyone is at risk of getting this new virus and they will be at greater risk of developing severe complications like pneumonia than they would be from seasonal ("ordinary") flu. Pandemic flu can appear similar to a seasonal flu in terms of symptoms: fever, headache, stuffy nose, aches, pains, sneezing, sore throat and cough.

A pandemic may last up to two years and, based on previous pandemics, may occur in waves. Each wave could last six to eight weeks and be separated by three to nine months.

Another difference is that the new virus may affect people who do not normally suffer from seasonal flu such as young, healthy adults. The very young, the elderly or those with a suppressed immune system may be at an even greater risk. High rates of illness and death are expected in a pandemic. These illnesses may have an impact on social and economic areas of our daily lives including the availability of food, supplies, or other goods, and may also include a possible loss of services such as hydro (power) or water.