Tuesday, September 23, 2014

MMWR: Estimating The Future Number of Cases In The Ebola Epidemic




# 9005



The much anticipated (and already telegraphed) MMWR report modeling the possible future number of Ebola cases in Liberia and Sierra Leone has now been published, and they paint a dire picture where between 550,000 to 1.4 million infections could result over the next four months if interventions are not successful.  


At the same time the CDC held a press conference where Director Dr. Thomas Frieden warned that these numbers are based on `month-old data’, don’t reflect current and future progress in controlling the outbreak, and that  these `worst-case’ scenarios are unlikely to unfold.


With a range of possibilities running from a few tens of thousands of cases to well over a million, everything hinges on the speed and effectiveness of international efforts to mitigate the spread of this virus.  And while one remains hopeful the tide in that endeavor has begun to turn, it is far too soon to know how much impact they will ultimately have, and how soon they will gain traction.


Which means  - where we really are, and how bad this outbreak becomes - is likely to remain uncertain for some weeks to come.


Given the vagueness of today’s case counts, I haven’t found any compelling reason to embrace any single one of these recently published models over the others.  That said, I don’t discount any of them, either. 


My personal take is that things on the ground are probably worse than we know, and it is going to take a herculean international effort – and more than a bit of luck – if this epidemic is to be brought under control anytime soon. 


Follow the link to read the full MMWR report.



Estimating the Future Number of Cases in the Ebola Epidemic — Liberia and Sierra Leone, 2014–2015

Early Release

September 23, 2014 / 63(Early Release);1-4

Martin I. Meltzer, PhD1, Charisma Y. Atkins, MPH1, Scott Santibanez, MD1, Barbara Knust, DVM2, Brett W. Petersen D2, Elizabeth D. Ervin, MPH2, Stuart T. Nichol, Ph.D2 , Inger K. Damon, MD, PhD2, Michael L. Washington, PhD1

Corresponding author: Martin I. Meltzer, National Center for Emerging and Zoonotic Infectious Diseases, CDC. E-mail: qzm4@cdc.gov; Telephone: 404-639-7778.


The first cases of the current West African epidemic of Ebola virus disease (hereafter referred to as Ebola) were reported on March 22, 2014, with a report of 49 cases in Guinea. By August 31, 2014, a total of 3,685 probable, confirmed, and suspected cases in West Africa had been reported. To aid in planning for additional disease-control efforts, CDC constructed a modeling tool called EbolaResponse to provide estimates of the potential number of future cases. If trends continue without scale-up of effective interventions, by September 30, 2014, Sierra Leone and Liberia will have a total of approximately 8,000 Ebola cases.

A potential underreporting correction factor of 2.5 also was calculated. Using this correction factor, the model estimates that approximately 21,000 total cases will have occurred in Liberia and Sierra Leone by September 30, 2014. Reported cases in Liberia are doubling every 15–20 days, and those in Sierra Leone are doubling every 30–40 days. The EbolaResponse modeling tool also was used to estimate how control and prevention interventions can slow and eventually stop the epidemic.

In a hypothetical scenario, the epidemic begins to decrease and eventually end if approximately 70% of persons with Ebola are in medical care facilities or Ebola treatment units (ETUs) or, when these settings are at capacity, in a non-ETU setting such that there is a reduced risk for disease transmission (including safe burial when needed). In another hypothetical scenario, every 30-day delay in increasing the percentage of patients in ETUs to 70% was associated with an approximate tripling in the number of daily cases that occur at the peak of the epidemic (however, the epidemic still eventually ends). Officials have developed a plan to rapidly increase ETU capacities and also are developing innovative methods that can be quickly scaled up to isolate patients in non-ETU settings in a way that can help disrupt Ebola transmission in communities. The U.S. government and international organizations recently announced commitments to support these measures. As these measures are rapidly implemented and sustained, the higher projections presented in this report become very unlikely.

(Continue . . . )

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