May 7, 2003 An international team of researchers has estimated that the fatality rate for SARS is considerably higher than some early estimates.
According to a paper published online today in The Lancet, which examines data from the first nine weeks of Hong Kong's epidemic, the case fatality rate, among those admitted to hospital, in patients 60 years of age and older is estimated to be far higher (43.3%, 95% confidence interval 35.2 to 52.4%) than those below 60 (13.2%, 95% confidence interval 9.8 to 16.8%).
Similar estimates were obtained using a second statistical estimation method: 55.0% (95% confidence interval 45.3 to 64.7%) for those aged 60 or older and 6.8% (95% confidence interval (95% confidence interval 4.0 to 9.6%) in those below 60.
This first published epidemiological analysis of the spread of the SARS virus also reveals that the incubation period of the disease - the time from catching it to displaying symptoms - averages six days, while the time from onset of clinical symptoms to hospital admission varies from five to three days, lowering over the course of the epidemic.
The authors of the research, from Imperial College London, Hong Kong University, Chinese University of Hong Kong and the Hong Kong health authorities, say that their determination of the key epidemiological determinants of the SARS outbreak should help inform the design of effective public health measures to stop its spread.
Professor Christl Donnelly, lead author of the paper from Imperial College London, comments: "Although this study shows that the fatality rate from SARS is higher than previously thought, we now know that public health interventions have been successfully reducing the spread of the disease. Key among these is the movement of those identified with SARS into hospital quarantine as swiftly as possible, and we urge that this measure continues to receive high priority."
The study found that after the initial phase of exponential growth in the number of cases, numbers fell to below 20 per day by 28 April 2003 as public health interventions instituted by the Hong Kong authorities helped slow the outbreak. These included encouragement to report to hospital rapidly after the onset of symptoms, contact tracing for confirmed and suspected cases, and quarantining, monitoring and restricting the travel of contacts.
The study also estimated the average admission to death time is 36 days, and average admission to discharge time is 23.5 days.
The authors warn that the coming warm season in Hong Kong brings an increased risk of seasonal dengue and influenza outbreaks, which may complicate a rapid diagnosis of SARS, They recommend that measures to limit further transmission, such as the shortening of the onset-to-admission interval should now be given high priority.
The researchers looked at 1,425 cases that had been reported up to 28 April 2003, all logged on the Hong Kong Hospital Authorty eSARS system and the Hong Kong Department of Health's Master List. From this an integrated database was constructed containing information on epidemiological, demographic and clinical variables. The outbreak was formally announced on 10 March and 122 deaths from SARS occurred in the study period.
Notes to editors:
1. Published online in The Lancet at 00.01 Wednesday 7 May 2003 at http://www.thelancet.com.
2. Consistently rated in the top three UK university institutions, Imperial College London is a world leading science-based university whose reputation for excellence in teaching and research attracts students (10,000) and staff (5,000) of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that enhance the quality of life and the environment - underpinned by a dynamic enterprise culture. Website: http://www.imperial.ac.uk.
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