Control policy optimisation for SARS and other emerging infections: characterising transmission dynamics and estimating key epidemiological parameters
The Severe Acute Respiratory Syndrome (SARS) outbreak of 2003 demonstrated the potential for the rapid global spread of a novel respiratory infection, whilst also showing how effective international scientific collaboration and simple public health measures could bring such an outbreak under control. SARSTRANS brought together data and public health expertise from the three largest SARS outbreaks (in Beijing, Hong Kong and Taiwan) with experts on infectious disease epidemiology from outbreak areas themselves and from France, the Netherlands and the United Kingdom. The shared experience of the whole project team led to new insights into the optimal control of SARS, new generic tools for outbreak analysis, and new epidemiological theory. These insights are already informing public health policy for future outbreaks.[+] Read More
(a) Number of cases of SARS in Beijing by date
of onset (n=1896) and dates of important control
measures, March-May 2003. (b) Daily estimates
of the effective reproductive number Rt with
95% confidence intervals where the grey region
indicates Rt 1. HCW, Health-care worker; PPE,
personal protective equipment; WHO, World Health
China Ministry of Health. Reproduced from Cowling BJ, Ho LM, Leung GM. Effectiveness of control measures during the SARS epidemic in Beijing: a comparison of the Rt curve and the epidemic curve. Epidemiology and Infection (2008), 136: 562-566.
Database structures, analytical tools and mathematical models were rapidly developed in response to the outbreaks and contributed to the effective control of SARS. However, there were still lessons to be learned for future similar outbreaks, such as how best to identify the similarities and differences between outbreak epidemiology in different regions, the underlying causes of super-spreading events and which control measures are likely to be most effective for future outbreaks.p
The aims of the SARSTRANS project were to:
SARS 2003: Data from Taiwan, Hong Kong and Beijing was brought together into a combined dataset which allowed comparative analysis of the three epidemics. There were similar patterns in incubation periods and agedistribution of cases in all three settings, but discrepancies in case fatality ratios. Reanalysis of a 'super-spreading' event suggested that the large number of cases attributed to a single source was likely to have been an overestimate caused by biased reporting. This highlighted the difficulty in identifying sources of exposure for a novel infection early in an outbreak.
Novel methods and tools for the analysis of outbreaks: Ideal database structures, methods for correctly estimating the case fatality ratio, the distribution of times from exposure to onset of symptoms and for real-time estimation of the potential scope of an outbreak, and the effectiveness of control measures from incidence data on a novel disease were developed and applied to existing datasets. An online tool for uploading and analysing outbreak data was developed for quantification of epidemics.
Other epidemiological analyses and lessons for future pandemics: During the course of this project, the collaborators were called upon to contribute to public health policy discussions during an outbreak of Chikungunya in Runion. They were also called upon to inform international planning for possible future outbreaks of influenza, smallpox or novel zoonoses. This led to many novel contributions to the theory of epidemics, including a new method of characterising the infectious potential of a disease which spreads between species.
The public health policy options considered include the following.
The proportion of contacts of diseased and detected individuals that should be traced to contain epidemics of influenza, SARS, and smallpox. It is assumed that the diseased cases are perfectly isolated upon detection and that the average numbers of secondary infections before detection were 1.5, 1.5, and 3, respectively. Adapted from Klinkenberg D, Fraser C, Heesterbeek H. The effectiveness of contact tracing in emerging epidemics. PLoS ONE 2006; 1: e12.
These results are informing public health planning for future outbreaks of airborne respiratory infections and furthering the understanding of such epidemics. In the event of a novel outbreak of emerging infection, or of a global influenza pandemic, the database structures, epidemiological analysis tools and the insights gained during this project will contribute substantially to the development of effective control programmes within the EU and elsewhere.