Nishiura Hiroshi, Schwehm Markus, Kakehashi Masayuki, Eichner Martin
Department of Medical Biometry, University of Tübingen, Westbahnhofstr 55, Tübingen 72070, Germany.
J Epidemiol Community Health. 2006 Jul;60(7):640-5. doi: 10.1136/jech.2005.042424.
The transmission potential of primary pneumonic plague, caused by Yersinia pestis, is one of the key epidemiological determinants of a potential biological weapon, and requires clarification and time dependent interpretation.
This study estimated the reproduction number and its time dependent change through investigations of outbreaks in Mukden, China (1946), and Madagascar (1957). Reconstruction of an epidemic tree, which shows who infected whom, from the observed dates of onset was performed using the serial interval. Furthermore, a likelihood based approach was used for the time inhomogeneous evaluation of the outbreaks for which there was scarcity of cases.
According to the estimates, the basic reproduction number, R(0), was on the order of 2.8 to 3.5, which is higher than previous estimates. The lower 95% confidence intervals of R(0) exceeded unity. The effective reproduction number declined below unity after control measures were introduced in Mukden, and before the official implementation in Madagascar.
While the time course of the latter outbreak could be explained by intrinsic factors and stochasticity in this remote and scarcely populated area, the former in Mukden suggests the possible continued chains of transmission in highly populated areas. Using the proposed methods, the who infected whom information permitted the evaluation of the time inhomogeneous transmission potential in relation to public health measures. The study also tackles the problem of statistical estimation of R(0) based on similar information, which was previously performed simply by counting the number of secondary transmissions regardless of time.
由鼠疫耶尔森菌引起的原发性肺鼠疫的传播潜力是潜在生物武器的关键流行病学决定因素之一，需要进行阐释并根据时间进行解读。
本研究通过对中国沈阳（1946年）和马达加斯加（1957年）的疫情爆发进行调查，估计了繁殖数及其随时间的变化。利用发病间隔时间，从观察到的发病日期重建了显示谁感染了谁的传播树。此外，对于病例稀少的疫情爆发，采用基于似然性的方法进行时间非均匀性评估。
根据估计，基本繁殖数R(0)约为2.8至3.5，高于先前的估计。R(0)的95%置信区间下限超过1。在沈阳采取控制措施后以及在马达加斯加正式实施控制措施之前，有效繁殖数降至1以下。
虽然马达加斯加疫情的时间进程可以用该偏远且人口稀少地区的内在因素和随机性来解释，但沈阳的疫情表明在人口密集地区可能存在持续的传播链。使用所提出的方法，通过谁感染了谁的信息可以评估与公共卫生措施相关的时间非均匀传播潜力。该研究还解决了基于类似信息对R(0)进行统计估计的问题，此前只是简单地通过计算二代传播数量而不考虑时间来进行估计。
