Scale-Free Distribution Found in SARS Epidemic in Singapore : Are the Superspreading Events Unusual?

概要

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A total of 201 probable cases of SARS reported during February 25-April 30, 2003 in Singapore were investigated. It was found that the distribution of direct secondary cases can be characterized by a scale-free power-law distribution. A simple stochastic model can reproduce the distribution reasonably well. At present, the transmission dynamics and its mechanism are not clear; however, the phenomenological observation implies that the superspreading events (SSEs) are not unusual in this type of disease. The power of the probability density function, f(m)∞m^<-γ>, observed in the Singapore epidemic is γ= 2.2, which shows that although the expected number of persons who will be infected from a particular patient is always finite, the patient who has transmitted the disease to this particular patient is a good candidate for the unknown source of SSEs. This finding highlights the importance of immediate action to find out the infection route, i.e., to find out who infected the disease to a particular patient if man-to-man infection has occurred. In order to prevent the outbreaks of SARS, the persons who had contacts with this source patient must be isolated as soon as possible, as well as those who had contacts with the initially found patient.
福井大学の論文
2004-03-31