“Flesh-eating bacteria”—science or hype?

The media are once again abuzz with cases of “flesh-eating bacteria”.  Stories about this condition (technically “necrotizing fasciitis”)  started making the rounds about ten or fifteen years ago, and they make great headlines (and, in all fairness, the incidence of the disease started to rise with the increase in people with damaged immune systems such as HIV patients, chemotherapy patients, and organ transplant patients).  Since the original stories, reporting has improved—we’ve evolved from “flesh-eating virus” to “flesh-eating bacteria”. It’s not much, but I’ll take it. To really understand this nasty disease, we need to step back and learn a little science.

First, some perspective.  There are an estimated 3.5 per 100,000 cases of necrotizing fasciitis and related diseases in the U.S. yearly (about 10,500 cases), and perhaps 2500 deaths. In contrast, “invasive pneumococcal disease”, caused by Streptococcus pneumoniae, causes about 4400 deaths per year, out of about 40,000 cases.  Necrotizing fasciitis is quite deadly, but relatively rare.

Necrotizing fasciitis (we’ll call it NF for now) is a bacterial disease.  Pathogenic bacteria can come from the environment, or even from ourselves. We are hosts for many species, many of which aren’t even known yet.  Some of these are harmless, some are beneficial, and some can cause disease given the proper conditions. Bacteria can harm us in a number of ways: they can directly invade and damage tissue, they can produce toxins, and they can cause our immune systems to react so strongly that our bodies are destroyed in the fight. (The specifics of all this are quite complex, too much to get into here.)

One of the most common pathogenic bacteria is group A streptococcus or GAS.  This is the most common cause of “strep throat”, these days a relatively benign disease.  But strep throat can give us hints of the potential of GAS.  Scarlet fever, a rash often associated with strep throat, is caused by a toxin produced by the bacterium. It’s not serious, but GAS can cause another, less-benign rash—the one seen in toxic shock syndrome (toxic shock syndrome and NF are not complications of strep throat).

NF can be caused by a variety of bacteria, but often the cause is GAS. We’ll use GAS alone for simplicity.  GAS can enter the skin through injuries or other skin disruptions such as chicken pox (which is vaccine-preventable) or IV drug use. With a bit of bad luck, the bacteria will get comfy and start producing some pretty useful (for the bug) toxins.  Some of them prevent our own white cells from eating the bacteria. This allows the bacteria to continue to destroy tissue.  Other toxins cause high fevers and shock.  With shock, blood pressure falls, which can cause further tissue damage as infected areas receive less blood and oxygen.  Low oxygen environments are also fertile ground for other dangerous bacteria that require oxygen-poor environments. White cells, already being inhibited by toxins, are further inhibited by low oxygen levels.

All this leads to a synergy and positive feedback loop, increasing tissue damage.  The infection can be unimpressive at first, but can rapidly lead to massive tissue destruction as the feedback loop progresses.

Antibiotics alone aren’t effective.   Since the blood flow is so poor to the affected tissue, antibiotics can’t really reach them, so surgical removal of affected tissue is the only real cure.  Due to the shock, most patients will require specialized care, often in an ICU.

Necrotizing fasciitis makes for good headlines (especially if the victim is a previously-photogenic young woman), but it’s relatively rare. As a physician, I treat all skin infections seriously, and so should you, but rarely is there cause for panic.

(NB: Don’t google Fournier’s Gangrene, another type of NF).

8 Comments

  1. saffronrose

     /  May 18, 2012

    I couldn’t help myself, my last name being Fournier.
    I’ll second the suggestion–you don’t really want to see any photos of it, much less read the description, if you happen to be a male with diabetes/alcohol abuse/both. However, clean up your act if you are.

  2. *gag* To be fair, You DID say not to google it.

    • Yeah, that’s called “schmuck bait”. Suddenly you’ve got an infected perineum on the screen. (The only reason I’m not going for the obvious pun is because my sunglasses are broken.)

  3. bethanyanddaniel

     /  May 19, 2012

    Holy cow, that looks unpleasant.

  4. A general rule in the press is “If it bleeds, it leads.” If it eats your skin and can be described in very horrifying terms that would make you go mad, it’s going to be on for weeks on end.

    This is why influenza gets less hype than HIV which gets less hype than anthrax mailings which gets less hype than Saddam Hussein’s smallpox stash: The inverse of the number of deaths or infections of that particular disease, with the last being nonexistent. 😉

  5. Saint Stay At Home

     /  May 28, 2012

    Reblogged this on ST. SAHM and commented:
    Great info! Circulating on our local news for the sixth week. Reblogging this DOES NOT mean I lack compassion for those actually affected (rather infected).

  6. i don’t see any hype out there, and i watch CNN a lot. in comparison, i’d much rather see a story about this than another accusation about obama’s birth certificate or another story in which mitt romney blames obama for everything that’s gone wrong in the past 20 years.

    • yeah, but it’s a medical blog.
      just read another story on one of the young women today, parents crediting prayer with her only being chopped to pieces, and finally able to utter a couple of words. How ’bout them docs and nurses, y’all?

%d bloggers like this: