The World Health Organization (WHO) has formally announced that a member of the coronavirus family never before seen in humans, named by WHO and its SARS laboratory network as the SARS virus, is the cause of severe acute respiratory syndrome (SARS) (1). An expert meeting in Geneva, attended by representatives from the SARS laboratory network, reviewed the data available on SARS, and considered the imminent strategy for development of a diagnostic test for SARS.

Among those present at the WHO press briefing that followed was Albert Osterhaus, director of virology at Erasmus Medical Center in Rotterdam, the Netherlands (2). Osterhaus reported an experiment in which three groups of monkeys were infected with cultured coronavirus alone, with metapneumovirus alone, and with coronavirus followed by metapneumovirus. Only the first group of monkeys, which were infected with coronavirus alone, developed SARS, including clinical symptoms and the pathological lesions seen in human patients who have died from SARS. The second group of monkeys, infected with metapneumovirus, developed mild rhinitis only, and the third group did not develop more serious disease.

WHO and the SARS laboratory network has now agreed that coronavirus alone is capable of causing the typical symptoms that have been seen in SARS cases.

The WHO and the network of laboratories dedicate their detection and characterization of the SARS virus to Dr Carlo Urbani, the WHO scientist who first alerted the world to the existence of SARS in Hanoi, Vietnam, and who died from the disease on 29 March 2003 (3).

In WHO's 27th update on the multicountry SARS outbreak, David Heymann, executive director of communicable diseases at WHO, made an overview of the situation, and applauded the remarkable international collaboration that has been seen since mid-March 2003 (4). He commented that the response to SARS has been the first test of global alert and response activity under the revision of the International Health Regulations (5). Early detection, and the rapid introduction of emergency measures to prevent further international spread of SARS, the issue of an unprecedented emergency travel advisory, and identification and characterisation of the causative agent, have all been results of international cooperation.