September 23, 2014

In a worst-case scenario, the number of Ebola virus disease (EVD) cases could swell dramatically to between 550,000 and 1.4 million in Liberia and Sierra Leone by January 20, 2015, according to an article published online today in the Morbidity and Mortality Weekly Report.

That scenario, however, is “very unlikely” because of rapidly expanding global efforts to contain and stop the epidemic, according to the article.

Martin I. Meltzer, PhD, from the National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention (CDC), and colleagues developed a modeling tool to help guide containment efforts in the fight against EVD.

In a teleconference today, CDC Director Thomas Frieden, MD, MPH, said the model “basically shows an unsurprising finding, which is that if cases continue to increase exponentially there will be a lot of them very soon. But the bottom line here, and what’s really important in this tool, is that the model shows…that a surge [in containment efforts] now can break the back of the epidemic.”

But that surge has to begin now, Dr. Frieden emphasized, because the costs of delay mount rapidly.

The CDC has about 120 people on the ground in Africa already, and the US Department of Defense has activated a joint force command on the ground in Monrovia, Liberia. The agencies’ efforts aim to make care available to more people through additional EVD treatment units and increased staffing. Other nations in Europe and Asia have launched similar efforts, as has the United Nations.

Dr. Frieden noted that the situation in Guinea is so unstable that the country could not be included in the CDC’s modeling tool.

Isolating 70% of Patients Is Key

In hypothetical scenarios, the CDC modeling tool shows that isolation is the key to controlling the outbreak.

“If, by late December 2014, approximately 70% of patients were placed either in [EVD treatment units] or home or in a community setting such that there is a reduced risk for disease transmission (including safe burial when needed), then the epidemic in both countries would almost be ended by January 20, 2015,” the authors write. “[O]nce 70% of patients are effectively isolated, the outbreak decreases at a rate nearly equal to the initial rate of increase.”

“The model shows several things that are encouraging, and 1 cautionary note,” Dr. Frieden said. “The first encouraging thing is that if you get enough people effectively isolated, the epidemic can be stopped. Related to that, when you reach a high enough number…the number of cases plummets rapidly, almost as the exponential rise we’re seeing now.

“The cautionary finding is the enormous cost of delay,” he continued. “For each month of delay, there’s a big increase in the number of cases, and it gets that much more difficult to control the epidemic.”

WHO Numbers “Bleak”

The CDC’s dire descriptions of a worst-case scenario follow on the heels of a warning from the World Health Organization (WHO) that unless epidemic control measures improve rapidly, the 3 countries most affected by EVD could soon start reporting thousands of related cases and deaths each week and could reach more than 20,000 affected people by early November.


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