WITH so many people already infected in so many places, and the disease spreading across China, hopes that SARS might be contained are fading.
Quarantining everyone who might carry the virus is now a daunting job. Despite the best efforts of Hong Kong, Singapore and Canada, with their modern healthcare systems, and draconian restrictions on people who might be infected, the spread has only been slowed, not stopped. The omens are not good for places with poorer healthcare systems.
One thing makes the task easier: the pattern of transmission so far suggests the virus is carried by large droplets that are coughed out, or perhaps shed in faeces. Crucially, unlike the very fine aerosol droplets that can carry the flu virus for long distances, larger droplets do not stay airborne for long. It seems that people have to be in close contact with someone who is infected, or touch contaminated objects such as lift buttons, to catch the disease.
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If SARS did spread via aerosols, says David Heymann, head of infectious diseases at the WHO, there would have been far more cases by now and they would include people without clear links to other sufferers. For example, In Hong Kong鈥檚 Metropole Hotel, SARS struck only guests on the same floor as the Chinese doctor Liu Jianlun who carried the virus from Guangdong. These people would have touched the same door handles, railings and elevator buttons. A viral aerosol might have reached guests from other floors in the hotel elevator. So frequent hand washing with soap probably gives better protection from the virus than the face masks that many are wearing in affected areas, a fact that has not been as well publicised.
The timing of when people can pass on the virus is crucial. If an infected person does not shed large numbers of viral particles until symptoms show, then containment is just a matter of isolating the obviously ill. But if someone can spread the virus before developing symptoms, or without ever becoming noticeably ill, it will be extremely difficult to contain SARS. And it does seem that people can spread the virus at very early stages of the disease. Liu spread it to fellow hotel guests even though he hurried to hospital as soon as he realised what he had.
If a cheap and rapid test can be developed, it might become possible to screen airline passengers before flights. But by the time such a test is available, SARS may have spread so far such screening would be pointless.
So does it matter if SARS becomes endemic? Some commentators have played down its seriousness, pointing out that the fatality rate is just 3.7 per cent (see Graphic). Yet some estimates suggest the mortality rate for the 1918 flu epidemic was just 4 per cent. SARS may spread far more slowly, but it could claim a heavy toll until good treatments are available.
In the long run, the best hope is a vaccine. Here the signs are good. There are vaccines against animal coronaviruses similar to the one thought to cause SARS (see 鈥淲here did this deadly pneumonia come from?鈥�), and work has already begun on a SARSvaccine. But such a vaccine is at least a year away.