Monday, 22 August 2011

Naegleria fowleri, Terror of Swimmers

It’s two thirds of the way through a long hot summer (in some places) and numerous swimming holes have had lots of time to warm up to temperatures well above average. Tragically, this sometimes results in deaths due to infection with Naegleria fowleri, especially in warmer regions such as the southern United States. Naegleria, sometimes referred to as the “brain-eating parasite,” is an environmental amoeba that can, given the opportunity, gain access to the human brain through the back of the nose.

Naegleria Thrives Where Water is Warm

Naegleria does not habitually parasitize humans, but it does multiply in warm waters, and if swimmers draw water up the nose, infection can follow. (This year, one victim reportedly infected himself using a neti pot – a device used to rinse the sinuses.) Once infected, very few people survive the dreadful illness that Naegleria causes. Victims, of course, are typically those who enjoy water sports and games – the young, fit, and healthy.

Deaths due to N. fowleri are often widely reported, especially now that we have the internet. After such a death, people call for disclosure of the bodies of water involved, more public education, and surveillance. This is entirely understandable, but these demands really do miss the point. Naegleria is an environmental organism, widely distributed in nature, and well known for multiplying in warm bodies of water. It could be in any warm water, even the stuff in your hot water tank (as in the neti pot story). We can’t eradicate it, or even pinpoint where it will turn up next except in the most general terms.

If you really want to avoid this risk (and it is a small small risk) don’t swim in water warmer than 80F (26.7C). Never draw warm water up your nose unless it has been sterilized. If there is a risk of drawing water up the nose, use nose plugs or a nose clip.

Naegleria Deaths in Perspective

The reality is that any activity carries a certain risk, even sitting at home. For comparison, the number of fatalities from N. fowleri in the United States in the decade from 2001 to 2010 is thought to be about 30, an average of three per year:

  • In that same time period, National Geographic reports that more than 400 people were killed by lightening.

  • In 2004, an average of nine people accidentally drowned per day in the United States (Poseidon).

  • In 2004, almost 4000 people died in fires, mostly residential.

  • Each year, more than 33,000 people are killed in automobile accidents in the United States (NHTSA).

Deaths due to N. fowleri are quick, horrifying, and tragic, but this disease shouldn’t be blown out of proportion. It’s rare. Exercise reasonable caution while swimming (submerged hazards, drowning, pathogens, dangerous aquatic animals etc.) and enjoy the summer.

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