Influenza is a contagious respiratory illness that is caused by different types of influenza virus. The flu is spread by coughs and sneezes, and can cause mild to severe illness, depending on which type of virus is responsible for the infection, and the health status of the infected individual. The best way to prevent the flu is by getting a vaccination each year, but antiviral medications can also be effective for people who are unable to get vaccinated.
Each year, about 10% to 15% of the population gets influenza, and up to 36,000 people die from the illness. Sometimes the flu is mistaken for a bad cold. The best way to tell if someone if suffering from influenza, rather than a cold, is by looking at their symptoms. The main differences between the flu and a bad cold are:-
  • The flu causes a dry feeling in the nose and throat, while colds cause a runny nose.
  • Muscular pains and shivering occur with the flu but not with a cold.
  • Flu symptoms can last for up to a week, while cold symptoms last for only one or two days.
  • The flu can cause very high fever, while colds only sometimes cause a mild fever.
Influenza outbreaks (epidemics) arise when there are minor changes in the nature of the virus. When this happens, it is more difficult for our bodies to recognise the virus, which means that more people become sick. Worldwide epidemics are called pandemics, and occur when there are major changes in the virus, and often cause many deaths.
There are three type of influenza virus:-
Influenza A virus causes illness in birds and mammals. It is rare in humans but can be very severe. This type of virus is often responsible for flu epidemics and also pandemics. 
Influenza B virus commonlyaffects humans. This virus is less severe than type A and causes epidemics, but not pandemics.
Influenza C virus causes mild illness in humans and also pigs. It is not associated with influenza epidemics or pandemics.
Influenza symptoms usually develop one to three days after infection with influenza virus. These symptoms include:-
  • High fever, chills and sweating.
  • Sore throat and dry cough.
  • Weakness and tiredness.
  • Headache, and generalised muscle and joint pains, such as in the legs and back.
  • Stomach symptoms such as nausea, vomiting and diarrhoea occur commonly in children but rarely adults.
A physician can diagnoses influenza based on these flu-like symptoms, and by considering the number of days that the symptoms have lasted. You may be tested for influenza, but this is not required for treatment, or for the prescription of influenza antiviral medication.
Treatment recommended for the flu includes:-
  • Drinking plenty of fluids. This usually means drinking enough water to maintain your normal urine output.
  • Taking paracetamol or aspirin to control any fever, aches and pains. Sometimes early use of antiviral medication can shorten the length and severity of influenza associated symptoms.
  • Avoid exposure to respiratory irritants such as dust, fumes or tobacco smoke. These can affect the throat and lead to severe coughing or difficulty breathing.
  • Bed rest until your fever has gone and your temperature has returned to normal for at least 48 hours.
Specific antiviral drugs that target influenza are now available. There are two influenza antiviral drugs recommended to treat influenza, and they can also be used for prevention. These are oseltamivir and zanamivir, which are effective against influenza A and B viruses.
Zanamivir (Relenza) is approved to treat influenza in people 7 years and older, and to prevent flu in people 5 years and older.Zanamivir can reduce the chance of getting the flu in people who spend a lot of time with someone who has the flu. Zanamivir can also reduce the chance of people getting the flu if there is an outbreak in the community. Some of the side-effects associated with Zanamivir include headache, diarrhea, nausea, vomiting, nasal irritation, bronchitis, cough, dizziness, and sinus, ear, nose and throat infection.
Oseltamivir (Tamiflu) is approved to treat and prevent flu in people one year of age and older. The most common side effects of oseltamivir are nausea and vomiting, and these are usually mild to moderate and happen in the first two days of treatment. A serious side effect to this drug can be confusion, and people, especially children, can be at increased risk of self-injury shortly after taking oseltamivir. After taking this medication, people should be monitored closely for signs of unusual behaviour.
For treatment, influenza antiviral drugs should be started within 2 days after becoming ill and taken for 5 days. When used this way, these drugs can reduce flu symptoms and shorten the time you are ill by between one and two days. Antiviral drugs can also make you less contagious and preventing influenza from spreading.
While most healthy people recover from the flu, some people, such as the young, elderly, or those with certain health conditions (such as asthma, diabetes, or heart disease) are at higher risk from influenza, and it is especially important for these people to be protected. The best way to prevent the flu is by getting a yearly influenza vaccination, which involves the administration of inactivated (dead) virus particles by injection. In Australia, annual vaccination is recommended from March to April, and protection usually develops two weeks after the injection, and lasts for up to one year. Immunisation with the influenza vaccine is recommended for people:-
  • At high risk of complications from the flu, such as children, pregnant women or people over 50 years of age.
  • With long-term medical conditions such as kidney, heart or lung disease, or diabetes.
  • Receiving immunosuppressive treatments such as long-term steroids.
  • In nursing homes and long-term care facilities.
  • Who have compromised immune symptoms, such as those with HIV.
  • Health care providers, nursing home staff, and anyone sharing a household with high-risk people.
A nasal-spray type vaccine is also available. This is made using live virus particles that are weakened, and do not actually cause the flu. This type of vaccine is used in healthy people that are between the ages 2 and 49, and who are not pregnant. People may choose this form of vaccination if they have allergies to the components of the injectable vaccination.
While antiviral medications can be effective at treating the flu or preventing infection with influenza virus, they are usually considered a second line of defence. Influenza antiviral drugs are very specific, and only work against influenza viruses. This means they do not help to treat or prevent symptoms caused from infection by any other type of virus that can cause symptoms similar to the flu. Antiviral medications are used in different settings and circumstances to treat or prevent influenza, which include:-
  • Places where many people who are at high risk of serious illness come into close contact with each other, such as nursing homes or hospitals.
  • Community settings where the goal is to reduce symptom severity and the number of days that people are ill.
  • For people that require protection from the flu when vaccination is unavailable or when they can not get the vaccine because of prior health conditions, such as allergies.
Serious complications of the flu are rare but can occur in children, older people, and those with previous health conditions. Complications are more common among people with an underlying medical condition or reduced immunity because flu can increase the risk of death or serious complication from the underlying disease. Complications of influenza can include:-
Bacterial pneumonia occurs when bacteria invade the lungs. Symptoms include shortness of breath, green-yellow phlegm, chest pains, fever and sometime blue discoloration of the skin (cyanosis).
Ear infection (otitis media) occurs when bacteria or viruses infect the fluid of the middle ear, which can cause pain, redness of the eardrum and occasionally fever.
Sinus infection (sinusitis) involves inflammation of the sinuses by the spread of respiratory infection. Influenza viruses can damage tissue, which makes them easily colonised by bacteria. Symptoms include nasal congestion, pain, fever, headache and fatigue.
The flu is spread mainly from person to person, often through the sneezing or coughing of people infected with influenza virus. Infected individuals usually begin infecting others about one day before symptoms develop, and up to five days after becoming ill. Unfortunately, this means that infected individuals begin to spread influenza before they know they are ill.
People can help to prevent the spread of influenza viruses by:-
  • Avoiding close contact with people who are sick, and staying away from others when you are sick.
  • Staying at home when you are sick. By staying away from work, or keeping children home from school, you will help to prevent others from catching your flu virus.
  • Covering your mouth and nose with a tissue when coughing or sneezing, as this can prevent those close to you from becoming ill.