Getting ill usually means suffering from something fairly familiar – tonsillitis, a cold, ‘flu or pneumonia. But on March 17 2003 the arrival of a new and potentially deadly disease was announced in the world media. SARS (severe acute respiratory syndrome) originated in the Guandong area of southern China but soon spread to Hong kong and from there to countries such as Canada and the USA.

The early symptoms of SARS are fairly vague. The sufferer has a fever of over 38 degrees C, and may have a headache, general body aching and discomfort – symptoms which could be any one of many familiar diseases. Over the first few days a dry cough and some difficulty breathing may develop. In many patients these symptoms gradually improve and they recover, but for some, particularly older people and people who have damaged immune systems, the infection can be fatal. SARS seems to be spread by close contact between people through droplet infection – most people who have fallen ill have lived with or cared for someone who is infected, or they have travelled on the same plane, close together for several hours.

A vital step in understanding how to treat, cure or prevent a new disease is knowing what causes it. This used to take months or even years. But within a week of the first outbreak of SARS scientists had a good idea what was causing it, and within a month they had sequenced the RNA of the virus involved. This was all made possible by PCR.

Specimens of body fluids taken from SARS patients were made available to scientists and the genetic material amplified using PCR. The RNA could then be sequenced and identified – the genetic material from the affected person and from known microbes eliminated, leaving the genetic material of the microbe causing SARS. It has turned out to be a new mutation of a coronavirus.

PCR is also very important in diagnosing SARS. The problem is that the symptoms are very easy to mistake for other diseases, yet SARS can be fatal. The World Health Organisation (WHO) is trying very hard to contain the disease and prevent it from spreading around the world. This means it is very important to know if someone is suffering from SARS so they and their contacts can be kept in isolation.

Diagnostic tests using antibodies are so far only effective about 10 days after infection – by which time the person will be either in intensive care, dead – or getting better. PCR is enabling doctors and scientists to get a much more rapid diagnosis. Two German scientists used PCR to amplify and so identify unique sections of the viral genetic material. They have developed probes which will attach to these sections and show them up. So material from a patient with suspected SARS is processed using PCR, and then the amplified genetic material is exposed to the SARS corona virus specific probes. This can show up infection before the disease has progressed too far, making it easier to provide effective treatment and to avoid further cross infection.

Dr Klaus Stuhr of the WHO has emphasised the way in which scientists throughout the international community have worked together, sharing results and ideas, to enable such rapid progress in identifying the SARS virus to be made. All the usual competition to be the first to publish results was set aside in the face of this global health emergency. The great fear is that SARS might spread to the African nations, where so many people already have weakened immune systems from the effects of AIDS. It could wipe out millions of people in a very short time.

The tests developed so far are still being refined and made more accurate – they are not completely reliable and there are even ideas that more than one virus might be involved. But thanks in no small part to the polymerase chain reaction, doctors and scientists have some early tools to help them deal with this new disease – and hopefully prevent it becoming a major disaster.