Posted on 04/25/2003 3:08:17 PM PDT by blam
SARS much more deadly than first estimated
13:43 25 April 03
NewScientist.com news service
Analysis of the latest statistics on the global SARS epidemic reveals that at least 10 per cent of people who contract the new virus will die of the disease.
The low death rates of about four per cent cited until now by the World Health Organization and others are the result of a statistical difficulty, well known to epidemiologists, that hampers the early analysis of new disease outbreaks. This difficulty is the reason for the apparent rise in death rate - not a change in the SARS virus.
A fatality rate of over 10 per cent puts SARS on a par with some other RNA viruses. Yellow fever and Japanese encephalitis, spread by tropical mosquitoes, between them kill more than 10,000 people a year, even though both have vaccines. Lassa fever kills about 70,000 a year in West Africa, but people mainly catch it from a local mouse.
Because these infections need animal vectors that only exist regionally, none has ever gone global. But the SARS vector - humans - is everywhere.
Draconian measures
The emergence of the true deadliness of SARS comes as further draconian measures are implemented by health authorities around the world.
The latest is the quarantining of 4000 people and the complete isolation of two hospitals in Beijing. China, where the virus emerged, has about half the world's known SARS cases, which have now risen to total 274 deaths and over 4800 infections.
The standard figure used to gauge the deadliness of any disease is the "case fatality rate" (CFR). This is the number of deaths divided by the number of cases of the disease.
Early in the SARS epidemic, the CFR was about four per cent. But the CFR calculated from statistics released on Thursday and Friday for Hong Kong, Canada and Singapore are now 7.6, 10.7 and 9.9 per cent respectively. These three places are the worst hit after the Chinese mainland.
The global CFR has risen steadily since the start of the epidemic but this is to be expected, say epidemiologists contacted by New Scientist. Early in an epidemic, a significant proportion of the total number of cases have neither recovered nor died. Some will eventually die and so move from the denominator to the numerator of the CFR, raising its value. The CFR moves towards the true value as time passes, unless the number of new cases explodes.
Better estimate
With many cases still unresolved, a better current estimate of the deadliness of SARS may be the number of deaths as a proportion of resolved cases. Those numbers for Hong Kong, Canada and Singapore are 15.8, 18.3 and 13.7 per cent. But these too could be misleading if, for example, it takes longer to recover from a disease than to die from it.
In China, this death rate is only 8.8 per cent. But statistics there are widely mistrusted, after Chinese authorities withheld nearly all information until recently. The Chinese statistics may also include cases of pneumonia due to bacterial infections, a widespread problem there, and which are cured with antibiotics.
One way to resolve the uncertainty over the death rate, say epidemiologists, would be to take a "cohort" of cases that start at the same time, and follow them until all have resolved. Several groups, including Roy Anderson and colleagues at Imperial College in London, plan to publish detailed epidemiological analyses shortly.
Uncertainty may dog the exact calculation, but it now seems clear that in the absence of a cure or a vaccine, SARS could eventually kill millions. The best hope is a vaccine. At a high-level meeting last week in Washington DC, every major vaccine company reported that it had begun a research programme.
Debora MacKenzie
Good luck.
But that doesn't make sense because viruses mutate all the time ---what could have been a fairly benign virus years ago may have converted into something more pathologic ---that's why there are constantly new colds and flus. I guess no one knows where this SARS came from yet ---if it's in some animal host, a wild resorvior ---maybe it's one of those viruses that doesn't make it's natural host very ill but is more dangerous to humans.
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