Evaluating Subcriticality during the Ebola Epidemic in West Africa.

Wayne T A Enanoria,Thomas M Lietman,Michael Deiner,Wui Ip,Sarah Ackley,Lee Worden,Ernest Mwebaze,Daozhou Gao,Fengchen Liu,James Scott,Travis C Porco

doi:10.1371/journal.pone.0140651

Abstract

The 2014–2015 Ebola outbreak is the largest and most widespread to date. In order to estimate ongoing transmission in the affected countries, we estimated the weekly average number of secondary cases caused by one individual infected with Ebola throughout the infectious period for each affected West African country using a stochastic hidden Markov model fitted to case data from the World Health Organization. If the average number of infections caused by one Ebola infection is less than 1.0, the epidemic is subcritical and cannot sustain itself. The epidemics in Liberia and Sierra Leone have approached subcriticality at some point during the epidemic; the epidemic in Guinea is ongoing with no evidence that it is subcritical. Response efforts to control the epidemic should continue in order to eliminate Ebola cases in West Africa.

Highlights

The 2014–2015 Ebola outbreak in West Africa is already the largest on record
We examined international reported Ebola case data to determine if and when the Ebola epidemic became subcritical in Liberia, Sierra Leone, or Guinea
The basic reproduction number, R0, the average number of secondary cases caused by one infected individual throughout the infectious period in a completely susceptible population, has been used to monitor epidemics of infectious diseases [10] including Ebola, with particular interest in when it decreases below 1.0 [11]

Summary

Introduction

Beginning with a case in Guinea in December 2013 [1], the outbreak extended to Liberia, Sierra Leone, Nigeria, and Senegal [2]. Activities, such as early diagnosis, patient isolation and care, contact tracing, infection control practices, and safe burials, are recommended strategies to reduce transmission and control the epidemic [3] and have been implemented in the affected countries. There have been reports citing evidence for a decrease in transmission of Ebola virus after the implementation of prevention and response measures [4,5,6], the precise time when control of an epidemic has been achieved is difficult to determine during the course of the epidemic. The disease has become subcritical and can no longer sustain itself in the population [7]

Methods

Results

Discussion

Conclusion