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

Gerardo Chowell, Cécile Viboud, James M. Hyman, Lone Simonsen

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While many infectious disease epidemics are initially characterized by an exponential growth in time, we show that district-level
Ebola virus disease (EVD) outbreaks in West Africa follow slower polynomial-based growth kinetics over several generations of
the disease.
We analyzed epidemic growth patterns at three different spatial scales (regional, national, and subnational) of the Ebola virus
disease epidemic in Guinea, Sierra Leone and Liberia by compiling publicly available weekly time series of reported EVD case
numbers from the patient database available from the World Health Organization website for the period 05-Jan to 17-Dec 2014.
We found significant differences in the growth patterns of EVD cases at the scale of the country, district, and other subnational
administrative divisions. The national cumulative curves of EVD cases in Guinea, Sierra Leone, and Liberia show periods of
approximate exponential growth. In contrast, local epidemics are asynchronous and exhibit slow growth patterns during 3 or
more EVD generations, which can be better approximated by a polynomial than an exponential function.
The slower than expected growth pattern of local EVD outbreaks could result from a variety of factors, including behavior
changes, success of control interventions, or intrinsic features of the disease such as a high level of clustering. Quantifying the
contribution of each of these factors could help refine estimates of final epidemic size and the relative impact of different
mitigation efforts in current and future EVD outbreaks.
TidsskriftPlos Outbreaks
StatusUdgivet - 2015
Udgivet eksterntJa

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