Influenza is an infection caused by the influenza virus. The virus infects the nose, throat and airways. There are many different viruses other than the influenza virus that can infect the respiratory tract, but the influenza virus tends to cause more severe disease.
Influenza viruses cause annual outbreaks that peak during the winter months. There are two main types of influenza that infect humans – influenza A and influenza B. There are currently two subtypes of influenza A circulating - H1N1 and H3N2. The current H1N1 subtype was introduced into humans in 2009 and initially caused an increase in severe disease. Since then it has continued to resurface each year and is now considered to be a routine seasonal flu subtype. H1N1 and H3N2 are both capable of causing severe disease and are both managed in the same way.
People with flu experience a sudden onset of high fever, aching muscles, headache and severe tiredness. They tend to have a dry cough, sore throat and runny nose. The fever and aching muscles help to differentiate influenza from a common head cold caused by other viruses.
Influenza virus is spread from person to person via droplets produced by infected people when they cough or sneeze. The virus can also be spread on hands. To prevent the virus spreading, people should cover their mouth and nose with a tissue when coughing or sneezing, and wash their hands frequently.
Each year 5% – 10% of adults and 20% – 30% of children will suffer from flu. This leads to a high level of missed work and school, which results in severe economic losses for a country. It also results in an increased cost for health care. Infection can result in hospitalisation and death amongst those at high risk for severe disease (see below). Worldwide it is estimated to cause 250 000 – 500 000 deaths each year.
Most people with flu will recover within 1 – 2 weeks, but some people will develop more severe disease with complications. These include ear infections, sinusitis, bronchitis and pneumonia (infection of the lungs). People with asthma, emphysema or heart failure can experience a worsening of their symptoms. Severe disease can lead to death.
Oseltamivir is an antiviral that can reduce the severity of the illness. Ideally is should be given within 48 hours of when the symptoms start. As there is concern about the development of resistance to oseltamivir, it is not usually recommended for people with mild disease. Oseltamivir is recommended for anyone who is severely ill (requiring hospitalisation) or those at risk for severe disease. People with mild disease should rest, and take analgesics (e.g. paracetamol) for fever and pain. If there is no improvement in symptoms or symptoms worsen, visit your doctor.
The best way to prevent infection and its complications is through vaccination. Safe and effective vaccines are readily available at pharmacies. Vaccination is especially important for people at high risk for severe disease, including pregnant women. The vaccine is safe to give in pregnancy. The vaccine can be used after the age of 6 months.
Testing for influenza is expensive. If you have mild symptoms, testing for flu will not change the recommended treatment. Testing is recommended for individuals who have been hospitalised or for ill individuals who are in contact with someone at high risk for severe influenza (e.g. health care workers, child care workers, caregivers of individuals at high risk). This helps to identify high-risk individuals who may need oseltamivir for early treatment as soon as symptoms start.
Please note: that the vaccine only prevents infection with influenza virus; it does not prevent other viral infections
