The ominous math of the Ebola epidemicBy Joel Achenbach, Lena H. Sun and Brady Dennis When the experts describe the Ebola disaster, they do so with numbers. The statistics include not just the obvious ones, such as caseloads, deaths and the rate of infection, but also the ones that describe the speed of the global response.
Right now, the math still favors the virus.
Global health officials are looking closely at the “reproduction number,” which estimates how many people, on average, will catch the virus from each person stricken with Ebola. The epidemic will begin to decline when that number falls below one. A recent analysis estimated the number at 1.5 to 2.
The number of Ebola cases in West Africa has been doubling about every three weeks. There is little evidence so far that the epidemic is losing momentum.
“The speed at which things are moving on the ground, it’s hard for people to get their minds around. People don’t understand the concept of exponential growth,” said Tom Frieden, director of the U.S. Centers for Disease Control and Prevention. “Exponential growth in the context of three weeks means: ‘If I know that X needs to be done, and I work my butt off and get it done in three weeks, it’s now half as good as it needs to be.’ ”
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