Transmission potential of primary pneumonic plague: time inhomogeneous evaluation based on historical documents of the transmission network

Abstract

Background: 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. Method: 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. Results: 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. Conclusion: 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.

A plague on five of your houses - statistical re-assessment of three pneumonic plague outbreaks that occurred in Suffolk, England, between 1906 and 1918

“…The results here also compare favourably with the R minor values of 0.9 for Mukden in 1946 and 1.1 for Madagascar in 1957 [3]. Finally, there was insufficient data to provide any statistical comparison with the time-decreasing R minor analysed by Nishiura et al .,[6] although it is noteworthy that all 3 index cases here infected only 1 other person.…”

Quantifying the transmission potential of pandemic influenza

“…Moreover, for simple epidemic models with relatively few parameters, R 0 can be estimated with other unobservable quantities by rigorous curve fitting of model equations to the observed epidemic data (discussed in Section 3) [38][39][40]. Not only R 0 but also R(t) can be estimated from the temporal distribution of infectious diseases, reconstructing the transmission network or inferring the time-inhomogeneous number of secondary transmissions [41][42][43][44].…”

Revisiting the Medieval Black Death of 1347–1351: Spatiotemporal Dynamics Suggestive of an Alternate Causation

“…Untreated PP case fatality is 95–100%, and infection to death occurs in 4–7 days; however, it is exceedingly rare, representing only 2% of all plague cases in USA from 1947 to 1996 (Inglesby et al 2000). This is likely due to its low basic reproduction number [defined as the number of secondary infections that are a result of one typical primary case in a completely susceptible population (Wallinga and Lipsitch 2007)] of R 0 = 1 (Kool 2005) or 2.8–3.5 (Nishiura et al 2006). Pneumonic Plague typically spreads from an initial case to just one or two additional susceptible people (Begier et al 2006; Seal 1969).…”