A Complexity Researcher Offers a Rather Gloomy Look at the Ebola Outbreak

The news cycle has moved on, it seems, yet Ebola is still kicking. According to a new statistical analysis, it's now kicking harder than ever.

The mortality rate for the current outbreak holds at near 70 percent—higher than the WHO's predicted 50 percent—while the rate of new infections remains exponential. Though previous WHO estimates had put the date at which the outbreak reaches 100,000 cases at Jan. 19, "updated statistics from September 6 advanced that date by at least a month," according to a report by Allen Hunt, a physicist at Wright State University in Ohio.

The unsettling conclusion of the analysis, published in the current issue of Complexity, is that the r_0 value (the number of secondary cases generated by every primary case) for the West African Ebola outbreak has recently begun increasing again. Any r_0 above 1 can be considered exponential growth, and any r_0 below 1 means the outbreak is controlled: x number of patients will generate < x new cases.

Given the data available in August, it appeared that r_0 had slipped to 1.51, a considerable improvement over the 2.25 seen in the outbreak's initial phase. Hunt explains, however, that according to the September figures, r_0 has climbed to 1.68.

Note: The y/vertical axis in the figure is logarithmic, not linear, like the Richter scale. As such, the plot below is not the straight-line steady growth it looks like, but a sharp upwards curve.

"That such an increase in transmission actually occurred is suggested by the fact that in the first 20 days of this increase in the case load, the exponential function for the death rate did not change," Hunt writes. "Including the potential underestimation of detected cases by the factor 1=4 advances the date for 100,000 cases 40 days to November 6, and a total of 1.6 million cases would be reached by January 25." Now, there are about 20,000, Hunt estimates, which means that successful tracking of individual patient contacts will take surveilling 500,000 people.

The new analysis is a worst-case, gloom and doom note of caution. Hunt notes that the report doesn't make any assurances about the outbreak's future growth rate, offering, "there is no certainty that the present exponential trends will continue and, indeed, hope that it will not." Other models have suggested the outbreak may slow down earlier, and in any case, the accuracy of any model can change based on how any mitigating response evolves.

As that half-million figure attests, however, the personnel demands of fighting Ebola remain staggering and probably beyond reasonable expectations. There isn't enough water for the fire, but still, that doesn't mean it can't be contained.