What is influenza?

Influenza (often called "the flu") is a respiratory disease that affects the nose, throat and lungs. It is caused by a virus that is easily passed from person to person. As with other viral illnesses, antibiotics do not work against an influenza virus. Antiviral medications may be used for treatment or prevention of influenza. Various strains of influenza virus circulate throughout the world each year. In Canada, seasonal influenza usually affects people during the winter, between November and April. Influenza viruses change slightly from year to year. Every year, seasonal influenza infects millions of Canadians. This has a significant effect on the health care system and school or work absenteeism.

An influenza infection lowers the body's ability to fight other infections. This can lead to pneumonia or bronchitis. Other health conditions such as diabetes, lung disease, heart disease, kidney disease and cancer can also make influenza worse. Most healthy people are able to recover from influenza without severe complications.

What is an influenza pandemic?

An influenza pandemic is declared when a new strain of influenza virus that has never been seen before emerges and begins to spread quickly around the world. People have little or no natural immunity to the new virus and large numbers of people become ill. An influenza pandemic occurs three to four times each century. The pandemic (H1N1) 2009 influenza virus is a new strain of the influenza A virus. This virus spread quickly around the world and in June 2009, the World Health Organization declared an influenza pandemic.

How is influenza spread?

Influenza spreads rapidly among people. The influenza virus passes from person to person by droplets when an infected person coughs or sneezes. Droplets travel through the air up to two metres (six feet) allowing the virus to enter the eyes, nose or mouth of people nearby. The virus can live on hard surfaces such as door handles, telephones, computer keyboards, light switches, countertops and soft surfaces such as clothing. Viruses can live on hard surfaces for up to 48 hours. Infection can occur when people touch any surface contaminated with the virus and then touch either their own mouth or nose, or someone else's mouth or nose, before washing their hands.

People usually develop symptoms of influenza within four days after becoming infected. They are usually contagious for seven days after the symptoms start. Children, especially younger children, individuals with weakened immune systems and those with severe illness may be contagious for a longer period, i.e. up to 10 days.

What are the symptoms?

Symptoms of influenza include:

• Fever of 38C (100.4F) or higher that starts suddenly;
• A dry cough that can last for weeks;
• Headache, pain in legs and lower back;
• Feeling weak and tired; and
• Some people may also experience nausea,
  vomiting and diarrhea.
• Fever of 38C (100.4F) or higher that starts suddenly;

Other symptoms can include:

• Chills;
• Loss of appetite;
• Sore throat; and
• Runny or stuffy nose.

Note:

• Fever may not be prominent in children younger
  than five years of age or those 65 years of age
  and older.
• Fever usually goes down and the person starts
  to feel better in three to five days. However,
  exhaustion and cough can continue for
  several weeks.
• Symptoms in babies may be hard to detect.
  For some babies, crying more than usual may be
  the only sign of illness.