Ng Tuen Wai, Turinici Gabriel, Danchin Antoine
Department of Mathematics, The University of Hong Kong, Hong Kong, China.
BMC Infect Dis. 2003 Sep 10;3:19. doi: 10.1186/1471-2334-3-19.
An epidemic of a Severe Acute Respiratory Syndrome (SARS) caused by a new coronavirus has spread from the Guangdong province to the rest of China and to the world, with a puzzling contagion behavior. It is important both for predicting the future of the present outbreak and for implementing effective prophylactic measures, to identify the causes of this behavior.
In this report, we show first that the standard Susceptible-Infected-Removed (SIR) model cannot account for the patterns observed in various regions where the disease spread. We develop a model involving two superimposed epidemics to study the recent spread of the SARS in Hong Kong and in the region. We explore the situation where these epidemics may be caused either by a virus and one or several mutants that changed its tropism, or by two unrelated viruses. This has important consequences for the future: the innocuous epidemic might still be there and generate, from time to time, variants that would have properties similar to those of SARS.
We find that, in order to reconcile the existing data and the spread of the disease, it is convenient to suggest that a first milder outbreak protected against the SARS. Regions that had not seen the first epidemic, or that were affected simultaneously with the SARS suffered much more, with a very high percentage of persons affected. We also find regions where the data appear to be inconsistent, suggesting that they are incomplete or do not reflect an appropriate identification of SARS patients. Finally, we could, within the framework of the model, fix limits to the future development of the epidemic, allowing us to identify landmarks that may be useful to set up a monitoring system to follow the evolution of the epidemic. The model also suggests that there might exist a SARS precursor in a large reservoir, prompting for implementation of precautionary measures when the weather cools down.
一种由新型冠状病毒引起的严重急性呼吸综合征（SARS）疫情已从广东省蔓延至中国其他地区乃至全球，其传播行为令人费解。确定这种行为的原因对于预测当前疫情的未来发展以及实施有效的预防措施都很重要。
在本报告中，我们首先表明标准的易感-感染-康复（SIR）模型无法解释该疾病在不同传播地区所观察到的模式。我们开发了一个涉及两种叠加疫情的模型来研究SARS近期在香港及该地区的传播情况。我们探讨了这些疫情可能由一种病毒以及一种或几种改变其嗜性的突变体引起，或者由两种不相关病毒引起的情况。这对未来具有重要影响：无害的疫情可能仍然存在，并时不时产生具有与SARS相似特性的变种。
我们发现，为了使现有数据与疾病传播情况相协调，不妨认为首次出现的较轻疫情对SARS起到了防护作用。未经历首次疫情的地区，或与SARS同时受到影响的地区遭受的影响要大得多，受影响人群的比例非常高。我们还发现一些地区的数据似乎不一致，这表明它们不完整或没有反映出对SARS患者的恰当识别。最后，在模型框架内，我们可以确定疫情未来发展的限度，这使我们能够识别出可能有助于建立监测系统以跟踪疫情演变的标志性事件。该模型还表明，在一个大的宿主群体中可能存在SARS的前身，这促使在天气转凉时实施预防措施。
