Possible symptoms and what to do if you fall ill

Symptoms of a future pandemic flu virus may follow past patterns of the disease, but they vary and no one can be certain because the new virus has not emerged yet.

Symptoms of seasonal flu include sudden onset, high fever of over 38C, headache, muscle pain, exhaustion, dry cough, chest discomfort and possibly sneezing and sore throat. Incubation period 2-3 days.

H5N1 flu virus mainly affects birds. Since 2003, 148 cases have been confirmed in humans in parts of Asia and Europe, including 79 deaths.

Human H5N1 infection is closely linked to contact with sick or dead birds, such as through slaughtering, defeathering or butchering them. It is not easily transmitted between humans. Virus experts fear it could mutate to do so and cause a severe world outbreak - a pandemic. If it does, it might change in other ways too, producing different symptoms and probably causing a lower death rate than the present 53 per cent.

This strain of bird flu is unusually aggressive in infected humans, with rapid deterioration and high fatality.

It causes influenza-like symptoms initially and in some patients diarrhoea, vomiting, abdominal pain, chest pain, nose and gum bleeding. Not all have respiratory symptoms. Two have had brain inflammation. Respiratory distress is common. Most develop pneumonia, commonly primary viral pneumonia, which, unlike secondary bacterial pneumonia, cannot be treated with antibiotics.

Pandemics vary. The 1918 Spanish flu pandemic infected up to 50 per cent of New Zealanders, of whom about 2 per cent died. It particularly afflicted otherwise healthy young adults, sometimes causing collapse and even death within hours of onset. By contrast, the 1957 pandemic infected up to 80 per cent, but the death rate was very low.

Medical advice on what to do if you think you have pandemic flu will not be issued until after a pandemic starts and the characteristics of the disease are known. For most it is likely to involve staying home, especially in a severe pandemic; others will probably be advised to contact a GP or go to a community-based assessment centre; and the worst affected will be hospitalised. The Government's Healthline, 0800 611-116, may play a key role.

Present advice on seasonal flu - apart from being vaccinated beforehand - may underpin pandemic advice. It centres on staying home, bed-rest, taking paracetamol for fever and drinking plenty of non-alcoholic fluids, including water, tea, soft-drinks or clear soup. Get up and move as soon as possible. The household should use good hygiene to minimise the risk of spreading the virus.

People with a chronic health problem like heart disease or diabetes might want to see a doctor - phone first - if they develop seasonal flu symptoms. Others should consider speaking to their doctor if they have green mucous that could indicate bacterial infection or are worried about a cough.

Tamiflu can reduce the severity and duration of seasonal flu if taken within 48 hours of onset. It can help with H5N1 bird flu and is expected to be useful in a future pandemic.

Sources: Auckland Regional Public Health Service, World Health Organisation.