Influenza

Influenza (or ‘the flu’) is caused by infection with influenza viruses A, B and rarely C. It mainly affects the throat and lungs, but can also cause problems with the heart and rest of the body, especially in people with other health problems. Influenza viruses regularly change, causing epidemics each winter in New South Wales. Every few decades a new type of influenza virus will emerge causing a severe and widespread epidemic (or pandemic).

Symptoms usually occur 1–3 days after infection, and may include sudden onset of fever, headache, muscle and joint pain, sore throat, cough, runny or stuffy nose and severe tiredness. Most people recover within a week. Compared with many other infections (like the common cold), influenza tends to cause more severe symptoms and complications, which can include pneumonia, heart failure or worsening of other illnesses.

The virus is mainly spread from person to person through droplets after an infected person coughs or sneezes, or through touching (e.g. when a person shakes hands with another). It is easier to catch influenza in confined or crowded spaces. A person with influenza is contagious from the day before, until a few days after symptoms begin.

Anyone can get influenza. Elderly people, those with other illnesses (such as heart disease, lung disease or diabetes) and small children are more likely to develop complications.

Anyone older than 6 months who wishes to avoid influenza should visit their general practitioner for a vaccination each year, before winter begins. Influenza vaccination is especially recommended for:

• adults aged 65 years and older

• Aboriginal and Torres Strait Islander people aged 15 years or older

• adults and children older than 6 months with chronic diseases affecting the heart, lungs, or that require regular medical follow up

• persons with certain neurological conditions

• persons with immunodeficiency, including human immunodeficiency virus (HIV) infection

• residents of nursing homes and other long-term care facilities

• homeless people and those who care for them

• adults and children older than 6 months who live in a household with a person who fits into any of the categories above

• health care workers

• staff, volunteers and frequent visitors of nursing homes and long-term care facilities

• people involved in the commercial poultry industry or in culling poultry during confirmed avian influenza activity

• people providing essential services

• children (6 months to 10 years) on long-term aspirin therapy

• people planning to visit parts of the world where influenza is circulating

• women who will be in the second or third trimester of pregnancy (even if already pregnant) between June and October.

It is important to note that:

• Children up to the age of 9 years require two doses at least 1 month apart in the first year they are vaccinated.

• It will take up to 2 weeks for the body to develop immunity after vaccination. The vaccine is designed to match the viruses likely to be circulating that winter. In otherwise healthy adults, the vaccine usually provides about 70–90% protection against infection for about 1 year.

• The vaccine is not recommended for some people, including those with allergies to eggs or who have had anaphylaxis following a previous dose of influenza vaccine or any vaccine component.

• Side effects can include soreness at the vaccination site, fever, fatigue and muscle soreness.

• The vaccine contains killed virus and so cannot cause influenza.

• People with a fever should delay vaccination until recovered.

• People who have previously had Guillain-Barré Syndrome should discuss vaccination with their doctor.

The vaccine is available free of charge to people aged 65 years or older and to Aboriginal or Torres Strait Islander people aged 50 years or older or aged 15 to 49 years with a chronic illness.

Based on symptoms and examination, a doctor can diagnose an influenza-like illness. The diagnosis of influenza can only be confirmed by testing a sample of the fluid from the back of the nose and throat, or a sample of blood. These tests are usually only needed if the illness is part of an outbreak, is unusually severe or there are complications.

Fever, headaches and muscle pains can be relieved with paracetamol and rest. Medications for influenza (oseltamivir and zanamivir) can reduce the severity and the duration of illness if taken within 2 days of the first symptoms. They are available only on prescription and are sometimes in short supply.

Laboratories must confidentially notify cases of influenza to the local public health unit. NSW Health also monitors the incidence of influenza in the community by tracking the number of people presenting to selected clinics with influenza-like illness, and the number of laboratory samples submitted to selected laboratories.

For more information please contact your doctor, local public health unit or community health centre.

This fact sheet is available at: http://www.health.nsw.gov.au/factsheets/infectious/influenza.html