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Influenza

Influenza, commonly known as flu, is a highly contagious respiratory illness caused by the influenza virus. The main viruses that cause influenza are influenza A and influenza B. They each have different strains. Each year there can be one or more strains of influenza circulating at the same time.

Influenza can occur at any time throughout the year, but the number of cases usually increases during the winter months. This is often referred to as the flu season.

Find out more about flu reporting.

Symptoms

Influenza symptoms usually come on quickly, within 1-3 days of contact with the virus, and tend to last for a week or longer.

Influenza can cause:

  • fever and chills
  • cough, sore throat, or runny nose
  • muscle aches, joint pains, headaches and fatigue (feeling tired)
  • nausea, vomiting and diarrhoea – more common in children than adults.

Some people can have very mild symptoms, particularly if they have immunity from a previous infection or from immunisation. However, some people may develop severe illness and need hospital admission. Complications from influenza include pneumonia, ear infection, heart and other organ damage, brain inflammation and brain damage, and death.

Those at highest risk of severe illness are pregnant women, young children, adults aged 65 years and older, and individuals with underlying chronic medical conditions.

Influenza infection is generally more severe than a cold. A cold usually has a slower onset and is less likely to cause complications.

Protecting yourself against influenza

Vaccination is the most effective way to protect yourself against becoming ill with influenza.

Yearly influenza vaccination is recommended (but may not be funded) for anyone 6 months of age and older who wishes to reduce the likelihood of becoming ill with influenza. It is also strongly recommended for people in contact with high-risk groups.

The influenza vaccine is free for people at higher risk of complications from influenza, including:

Find out more about flu vaccinations.

Diagnosis

A doctor can diagnose influenza based on the symptoms. The diagnosis can be confirmed by a laboratory test. The test requires a sample to be collected from the back of the nose or throat (using a special swab). This test is the most accurate way to test for influenza infection.

Treatment

People with influenza should rest and drink plenty of fluids, and treat symptoms as they occur. Antibiotics are not effective against influenza viruses.

If you are at high risk of severe illness from the influenza, speak to your doctor as soon as you start to feel unwell. There is antiviral medication that can reduce the effects and duration of influenza but it works best when taken early after symptoms begin.

Go to the Healthdirect website to learn more about antiviral medication tamiflu, or talk to your doctor. Tamiflu does not take the place of the yearly influenza vaccination.

Children under 16 years of age should not be given aspirin-containing medications while ill with influenza. Aspirin use in children can increase the risk of Reye Syndrome, which is a form of encephalitis (brain swelling) and liver degeneration.

How influenza is spread

People with influenza are generally infectious for 5 days after symptoms first appear, though children and those with weakened immune systems may be infectious for longer.

Influenza virus is spread easily from person to person through small droplets that are produced when an infected person coughs or sneezes. Droplets can settle onto surfaces, such as door handles and hand rails, and infect other people when they touch those surfaces.

Stopping the spread of influenza

If you are unwell with influenza, take action to stop its spread by:

  • frequently washing your hands (with soap and water) or use an alcohol-based hand rub, especially after coughing, sneezing or blowing your nose
  • staying away from work, school, child care and other public places while you are infectious (while you have a fever and for 24 hours after your fever resolves)
  • covering your nose and mouth when you cough or sneeze
  • throwing tissues straight into the bin after using them.

If you need to see your doctor, call ahead first and let them know you might have influenza.  To prevent spreading the infection to others, you may be asked to wear a mask over your  nose and mouth and to stay at least one metre away from others.

When unwell, you should avoid close contact with other people, particularly those at high-risk of severe illness, to prevent them becoming unwell. You should also avoid visiting people in aged care facilities (nursing homes), residential care facilities, correctional institutions, and hospitals.

Outbreaks of influenza

Influenza is highly infectious and can cause outbreaks in settings where lots of people live or work close together.

This can include:

  • aged care facilities (nursing homes)
  • other residential care facilities (such as rehabilitation units)
  • hospitals
  • child care centres
  • boarding schools
  • correctional facilities
  • military bases.

In these high-risk settings, the best way to prevent outbreaks is to ensure as many people as possible including staff, visitors and residents are vaccinated against influenza each year.

It is also very important that people do not attend/visit these settings when they are unwell.

When outbreaks do occur in these settings, the Health Protection Service provides infection control advice and recommends additional measures called outbreak precautions that are put in place to limit the spread of influenza.

These can include:

  • isolation or exclusion of unwell individuals until they are no longer infectious (usually 5 days)
  • limiting non-essential visitors and the movement of individuals through the setting
  • limiting or cancelling group activities
  • increasing the frequency of cleaning, particularly frequently touched surfaces such as door handles, light switches, hand rails.

Find out more about outbreaks of influenza in aged care settings and outbreaks of influenza in childcare settings.

More information

Influenza is a notifiable condition. For more information about influenza, contact your GP or call the Health Protection Service, Communicable Disease Control Information Line during business hours on 02 5124 9213.

Acknowledgements

Australian Technical Advisory Group on Immunisation (ATAGI), The Australian Immunisation Handbook 10th edition, 2017 update, Canberra, Australian Government Department of Health.