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

Joseph R Egan

doi:10.1186/1742-4682-7-39

Abstract

BackgroundPlague is a re-emerging disease and its pneumonic form is a high priority bio-terrorist threat. Epidemiologists have previously analysed historical outbreaks of pneumonic plague to better understand the dynamics of infection, transmission and control. This study examines 3 relatively unknown outbreaks of pneumonic plague that occurred in Suffolk, England, during the first 2 decades of the twentieth century.MethodsThe Kolmogorov-Smirnov statistical test is used to compare the symptomatic period and the length of time between successive cases (i.e. the serial interval) with previously reported values. Consideration is also given to the case fatality ratio, the average number of secondary cases resulting from each primary case in the observed minor outbreaks (termed Rminor), and the proportion of individuals living within an affected household that succumb to pneumonic plague via the index case (i.e. the household secondary attack rate (SAR)).Results2 of the 14 cases survived giving a case fatality ratio of 86% (95% confidence interval (CI) = {57%, 98%}). For the 12 fatal cases, the average symptomatic period was 3.3 days (standard deviation (SD) = 1.2 days) and, for the 11 non index cases, the average serial interval was 5.8 days (SD = 2.0 days). Rminor was calculated to be 0.9 (SD = 1.0) and, in 2 households, the SAR was approximately 14% (95% CI = {0%, 58%}) and 20% (95% CI = {1%, 72%}), respectively.ConclusionsThe symptomatic period was approximately 1 day longer on average than in an earlier study but the serial interval was in close agreement with 2 previously reported values. 2 of the 3 outbreaks ended without explicit public health interventions; however, non-professional caregivers were particularly vulnerable - an important public health consideration for any future outbreak of pneumonic plague.

Highlights

Plague is a re-emerging disease and its pneumonic form is a high priority bio-terrorist threat
All of these outbreaks are well documented and have been described as “unique to western Europe” [8]. They have been reported in previous papers, this study uniquely analyses the statistical epidemiology of the 3 pneumonic plague outbreaks
It is important to note that Dr Carey, who attended cases in all 3 outbreaks, undoubtedly encouraged barriers to close contact which may have implicitly affected the epidemiology of each outbreak

Summary

Introduction

Plague is a re-emerging disease and its pneumonic form is a high priority bio-terrorist threat. Pneumonic plague is a disease that poses a threat to both civilian and military populations either via a biological aerosolised release or through zoonotic transmission [1]. Such routes of infection are not mutually exclusive since a biological attack in a nonendemic plague region could lead to reservoirs of plague-infected animals after the initial human infections have been controlled [2]. The most likely explanation for these outbreaks is that grain brought from ports in the Black Sea and the Americas contained plague-infected rats which lead to enzootic rat-flea plague cycles All of these outbreaks are well documented and have been described as “unique to western Europe” [8]. Unlike recent analyses, [10,11,12] the natural history and transmissibility of the Suffolk cases were unaffected by effective treatment since antibiotics were not available until ~30 years after the last Suffolk outbreak

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