It is a new type of atypical pneumonia* that infects the lungs, caused by a new strain of coronavirus.

Atypical pneumonia refers to an infection of the lung that is caused by certain organisms such as Mycoplasma, Legionella and Chlamydia. SARS is a type of atypical pneumonia.

As more information has become available, WHO has revised the SARS case definitions as follows:

• Suspect Case
  A person presenting after 1 February 2003 with history of high fever (>38C) and one or more respiratory symptoms including cough, shortness of breath, difficulty breathing AND one or more of the following:
  • close contact* with a person who has been diagnosed with SARS
  • recent history of travel to areas reporting cases of SARS

  
  (* close contact refers to having cared for, having lived with, or having had direct contact with respiratory secretions and body fluids of a person with SARS)

  The travel or close contact history are key criteria in suspecting the diagnosis and helps distinguish SARS from other causes of fever and cough such as the common cold or the flu.
   

• Probable Case
  A suspect case with chest x-ray findings of pneumonia or Respiratory Distress Syndrome or a person with an unexplained respiratory illness resulting in death, with an autopsy examination demonstrating the pathology of Respiratory Distress Syndrome without an identifiable cause.

Treatment
Largely supportive. At present, patients are being treated empirically with antibiotics and in some cases, anti-viral agents.