The Western Africa Ebola virus disease epidemic exhibits both global exponential and local polynomial growth rates

摘要

Background: While many infectious disease epidemics are initiallycharacterized by an exponential growth in time, we show that district-levelEbola virus disease (EVD) outbreaks in West Africa follow slowerpolynomial-based growth kinetics over several generations of the disease.Methods: We analyzed epidemic growth patterns at three different spatial scales(regional, national, and subnational) of the Ebola virus disease epidemic inGuinea, Sierra Leone and Liberia by compiling publicly available weekly timeseries of reported EVD case numbers from the patient database available fromthe World Health Organization website for the period 05-Jan to 17-Dec 2014.Results: We found significant differences in the growth patterns of EVD casesat the scale of the country, district, and other subnational administrativedivisions. The national cumulative curves of EVD cases in Guinea, Sierra Leone,and Liberia show periods of approximate exponential growth. In contrast, localepidemics are asynchronous and exhibit slow growth patterns during 3 or moreEVD generations, which can be better approximated by a polynomial than anexponential. Conclusions: The slower than expected growth pattern of local EVDoutbreaks could result from a variety of factors, including behavior changes,success of control interventions, or intrinsic features of the disease such asa high level of clustering. Quantifying the contribution of each of thesefactors could help refine estimates of final epidemic size and the relativeimpact of different mitigation efforts in current and future EVD outbreaks.