What is Sars?
Sars stands for Severe Acute Respiratory Syndrome. It is a new illness that emerged in the Far East early in 2003, first in southern China, then spreading to Hong Kong, Vietnam, Singapore, Canada and more than 20 other countries.
It is believed to be caused by a new strain of Corona virus - a family of viruses which has been linked to the common cold.
By the middle of April, it had killed more than 150 people worldwide and infected more than 3,000 more.
What are the symptoms, and how is it treated?
The most obvious symptoms of Sars are breathing problems. Patients develop a high temperature (more than 38 degrees), dry cough, and severe respiratory symptoms follow swiftly.
Some patients need to be put on a ventilator to keep them breathing while their bodies fight the infection. Four in every hundred people who develop Sars do not survive.
Most of those who have died have been older, or had pre-existing health problems which increased their vulnerability - but some younger, healthy people have died.
Patients suspected of having Sars are given a combination of antibiotics and antiviral drugs, which have produced an improvement in some patients, although their precise effectiveness is uncertain.
There is no vaccine for the virus that causes Sars, although a diagnostic test has been developed.
How can I catch it?
The virus appears to be transmitted less easily than conventional influenza - although the resulting illness can become more severe.
It appears to be passed on by "close contact" with an infected person, perhaps carried in large droplets thrown out when the infected person sneezes or coughs.
There has been concern about transmission within passenger aircraft. The latest advice suggests that those at risk of infection would need to be seated within a couple of rows of the infected person, with no evidence of risk to people sitting elsewhere on the plane.
People in the Far East have attempted to protect themselves by wearing face masks - it is uncertain how much genuine protection these offer against the virus.
Should I avoid any particular areas?
The areas worst hit by Sars are Hong Kong, and the Guangdong province of southern China.
In late March 2003, the World Health Organization advised people to restrict non-essential travel to Hong Kong or Guangdong. The UK government agreed with this advice. This was only intended to be temporary advice until outbreaks in these locations were under control.
Travellers should check the websites of the World Health Organization and, in the UK, either the Health Protection Agency or Foreign and Commonwealth Office for the latest advice.
All travellers to areas heavily affected by Sars should be aware of this and take account of the problem in their travel plans. Some countries have been screening passengers arriving from Sars-hit areas for early signs of the illness.
I have some of these symptoms. What should I do?
If you have recently returned from South East Asia and suffer from any of the following symptoms - sudden onset of fever (>38° C), together with respiratory symptoms such as cough, sore throat, shortness of breath or difficulty breathing within 10 days of return, please contact your doctor's surgery or, in the UK, phone NHS Direct on 0845 4647.