Risk and brain amoebas

We humans are poor at assessing risk.

It's something I've commented upon before; we tend to vastly overestimate the likelihood of being harmed by something gruesome and unusual (such as a shark attack), while vastly underestimate the likelihood of being harmed by something commonplace (such as smoking).  This leads to missed opportunities and unnecessary anxiety in the first case, and ignoring truly dangerous behaviors in the second.

This comes up because of an article I've seen posted now several times, about an Ohio teenager who died from an infection by the "brain-eating amoeba" Naegleria fowleri.  The 18-year-old victim appears to have been infected while on a whitewater rafting trip near Charlotte, North Carolina, and several days later came down with the fever, chills, and headache associated with primary amoebic meningioencephalitis, which is as horrifying as it sounds.  The microorganism gets into your system through inhaled water, and it travels through the olfactory nerves to the brain.  There it turns from eating its usual food source, bacterial films in freshwater sediments, to consuming your brain cells.  The disease has a 97% mortality rate.

Naegleria fowleri [image courtesy of the CDC]

Unfortunately, the story (although correctly reported, for the most part) is inducing widespread hysteria from people who evidently missed the following line: "The CDC reported 37 infections in the 10 years from 2006 to 2015."  Let me put that statistic a different way; given the current population of the United States (318 million), that amounts to about one death per hundred million people per year.  Even if there were three times as many cases that go unreported -- unlikely, given the severity of the symptoms and the likelihood of dying as a result -- it's still a tiny, tiny risk.

Interestingly, these numbers are ten times smaller than the likelihood of your being crushed to death by a piece of your own furniture (303 deaths in the last ten years).

So here are a few of the comments I've seen posted in the last couple of days, edited to reflect the far more likely scenario of your being killed by a falling television cabinet.  I've inserted "television watching" and equivalent phrases for "swimming" and "hard hat" for "nose plug."

• I wish I hadn't read about this!!!  I'm never sitting in front of an unsecured television cabinet again.
• Just in time for summer.  So much for television watching.
• They should post warning signs on television cabinets!  It could have prevented this tragedy.
• Every time I'm sitting in front of the television, I'm gonna think about this.
• I'm protecting my kids from this.  They'll never watch television again without wearing a hard hat.

There.  I hope that sounded as ridiculous to you as it did to me.  And remember; there is ten times the justification for making those statements as there is for making equivalent statements about brain-eating amoebas.

Note that I'm not trying to minimize the tragedy of what happened.  A young life cut short is always sad, especially given how unlikely an occurrence it was.  What is completely unjustified is the panic that these sorts of stories always induce, even in people who should know better.  The U.S. National Whitewater Center, where the young woman is thought to have been infected, has responded by hyperchlorinating their well water, and health officials in North Carolina have recommended "holding your head above water when taking part in warm freshwater activities" and "avoid(ing) water-related activities in warm freshwater during periods of high water temperature and low water levels."

So when are you supposed to go swimming?  January?

The bottom line is that everything you do is a risk.  Most of the risks are quite small, and chances are that you do several things every day without a thought that are orders of magnitude riskier than your being killed by brain amoebas.  If you really want to lower your risk of illness and death, quit smoking, eat a healthy diet, drive carefully, find ways to reduce your stress levels, and get enough exercise.

And keep an eye on any unsecured television cabinets.  They're just waiting for an opportunity to strike.