Serving the Flathead Valley & Montana since 2006. A reality based independent journal of observation & analysis. © James Conner.

 

19 October 2014

On Ebola, present the facts and forego the preaching

Updated 30 October. Speaking about the Ebola virus in his radio address yesterday, President Obama said:

…we have to keep this in perspective. As our public health experts point out, every year thousands of Americans die from the flu.

That’s a common comparison, but not entirely apt — and a bit misleading.

Thousands do die each year from influenza and complications thereof, while so far only one person in the U.S. has died from Ebola. But influenza, which is much more contagious, kills a much smaller percentage of those who catch it than does Ebola.

According to the World Health Organization, as of 14 October the official Ebola death toll in Africa was 4,555 out of 9,216 cases in seven countries. One’s odds of surviving the disease without the rare and expensive experimental drug ZMapp are even, a coin toss. With ZMapp, the odds of surviving seem higher, but are not yet reliably quantifiable.

One’s odds of surviving influenza are on average much higher. During the 1918–19 Spanish Flu pandemic, 675,000 Americans died. One in 67 American servicemen died, reported John Berry in The Great Influenza; not every serviceman was infected. If 25 percent of the population caught the disease, 2.6 percent of those catching it — roughly one in 40 — died. Today, a much smaller percentage of those who catch influenza die from it (finding a solid figure is difficult).

The probability of dying from a disease once infected with it is just one of three probabilities employed to calculate the probability of health person’s dying from the disease. The other two probabilities are the probability of being exposed to the disease, and the probability of becoming infected once exposed. The equation is [Pe * Pi * Pd = Overall Probability of Dying].

Updated. For Ebola in America, Pe is very low, Pi is low but significant, and Pd is high, on the order of one or two in four or five (a very rough estimate) but the recoveries of infected Americans suggests that with treatment in our special medical facilities, patients have a better chance of surviving than once thought. For influenza, Pe is considerably higher than for Ebola, Pi is probably higher, but Pd is much lower than for Ebola.

That’s why reminding Americans that influenza and automobile accidents kill thousands more Americans than Ebola does nothing to make Ebola less frightening. People are thinking, “If I catch Ebola,” the odds that I’ll die from it are just about even. They are not factoring in the probability of being exposed to Ebola, which for most of us is just about zilch (but a lot higher for health care workers assigned to an Ebola case).

This is neither hysteria nor panic. It’s humankind’s instinctive approach to evaluating a threat. Our initial question is, “if this happens to me, what is the likely outcome?” If the outcome is dire, our next question is “how likely is this to happen to me?” followed by “do I need to modify my behavior to reduce the probability this will happen to me, and if so, how and by how much?”

What Americans need from their leaders are not patronizing assurances or gratuitous appeals for calm, but enough information that they can act in their enlightened self-interest. Present the facts, and forego the preaching.