Dr Muiris Houston, Medical Correspondent, reports on severe acute respiratory syndrome
The World Health Organisation rarely declares an illness "a world-wide health threat" - yet this was its response at the weekend after reports of more than 400 suspected cases of severe acute respiratory syndrome (SARS).
Cases were originally reported from Canada and three countries in Asia - China, Singapore and Vietnam. Last night, it was confirmed that a suspect case had been hospitalised in Britain. A doctor from Singapore, who had treated one of the earliest cases there, was taken off a flight in Frankfurt on Saturday after he became unwell while en route from New York to Singapore.
So what are we to make of this flurry of disease activity? Although neither the Centre for Disease Control in Atlanta nor any other health agency has so far been able to accurately identify an organism, the pattern of illness strongly suggests an infectious disease. And even allowing for the little we know about the illness to date, it is likely that some new strain of virus will eventually emerge as the culprit.
Since last November, there have been sporadic cases of an avian-type influenza virus in China.
However, experts have clearly labelled a case in Hanoi, Vietnam, on February 26th as the index case for the outbreak of SARS. On that date, a man was admitted to hospital with a high fever, dry cough, muscle pain and sore throat. Within four days he had developed severe breathing difficulties, a significant drop in the number of essential blood cells in his body and signs of respiratory distress syndrome for which he needed ventilatory support. He died on March 13th.
On March 5th, seven healthcare workers who had cared for the Vietnamese man also developed symptoms. By last Saturday 43 cases had been reported in Vietnam. All cases to date are linked to the hospital where the patient who initially developed SARS was cared for.
In Hong Kong, 20 healthcare workers developed the illness on March 12th. Three cases of SARS were reported in Singapore the following day, all of whom had returned from Hong Kong.
In Canada, seven cases of the illness were reported in two extended families. In each case, at least one family member had returned from Hong Kong within a week of developing symptoms.
It is understood that the British patient had been in Asia within the last 10 days.
Although we do not yet know the exact cause of this illness, a number of characteristics have emerged. It is flu-like in nature, and it appears to have an incubation period of two-seven days. Those most at risk are healthcare workers and family members of those who have contracted it.
It appears to require direct contact with respiratory secretions and body fluids for person-to-person transmission to occur. Unlike influenza epidemics, sharing a crowded bus, train or plane does not seem to trigger cross-infection.
If air crew and passengers who were present on flights which carried known cases of the illness remain disease free, then the outbreak is unlikely to represent the begining of a world-wide influenza epidemic. Some other virus is likely to be identified.