Small Michael, Tse C K, Walker David M
Department of Electronic and Information Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
Biomathematics and Statistics Scotland, Macaulay Institute, Craigbuckler, Aberdeen AB15 8QH, UK.
Physica D. 2006 Mar 15;215(2):146-158. doi: 10.1016/j.physd.2006.01.021. Epub 2006 Mar 10.
We describe a stochastic small-world network model of transmission of the SARS virus. Unlike the standard Susceptible-Infected-Removed models of disease transmission, our model exhibits both geographically localised outbreaks and "super-spreaders". Moreover, the combination of localised and long range links allows for more accurate modelling of partial isolation and various public health policies. From this model, we derive an expression for the probability of a widespread outbreak and a condition to ensure that the epidemic is controlled. Moreover, multiple simulations are used to make predictions of the likelihood of various eventual scenarios for fixed initial conditions. The main conclusions of this study are: (i) "super-spreaders" may occur even if the infectiousness of all infected individuals is constant; (ii) consistent with previous reports, extended exposure time beyond 3-5 days (i.e. significant nosocomial transmission) was the key factor in the severity of the SARS outbreak in Hong Kong; and, (iii) the spread of SARS can be effectively controlled by either limiting long range links (imposing a partial quarantine) or enforcing rapid hospitalisation and isolation of symptomatic individuals.
我们描述了一种非典病毒传播的随机小世界网络模型。与疾病传播的标准易感-感染-康复模型不同，我们的模型既呈现出地理上局部爆发的情况，也出现了“超级传播者”。此外，局部连接和长程连接的结合使得对部分隔离措施和各种公共卫生政策进行更精确的建模成为可能。基于这个模型，我们推导出了广泛爆发概率的表达式以及确保疫情得到控制的条件。此外，通过多次模拟对固定初始条件下各种最终情况发生的可能性进行预测。本研究的主要结论如下：（i）即使所有感染者的传染性恒定，“超级传播者”仍可能出现；（ii）与之前的报告一致，超过3至5天的延长暴露时间（即显著的医院内传播）是香港非典疫情严重程度的关键因素；以及，（iii）通过限制长程连接（实施部分隔离）或强制对有症状个体进行快速住院和隔离，非典的传播可以得到有效控制。
