Today we had our first onslaught of Medical Microbiology, a course that I already find quite interesting: if not for the subject itself, at least I know that my future pursuits will require that I have a very solid knowledge of infectious diseases (especially nosocomial, or hospital-acquired, infections). After today’s introduction and overview of the course, we launched into the two large Gram-positive bacteria families: the Staphylococcus and Streptococcus species, together accounting for large proportion of morbidity and mortality due to infectious diseases directly or indirectly as complications of other diseases (i.e. chronic, autoimmune, etc.).
The Staph family is responsible for a wide variety of diseases from skin infections to fatal conditions such as endocarditis (inflammation of the inner walls of the heart), septic shock, toxic shock syndromes, and pneumonias. The most famous Staph is MRSA, or Methicillin-resistant Staphylococcus aureus, a strain resistant to many antibiotics that is frequently found in cases of both community-acquired infections and hospital-acquired infections. Meanwhile, the Strep family is similarly responsible for a broad spectrum ranging from impetigo (a skin infection involving “honey-crusted” lesions) to pharyngitis (strep throat) to pneumonia to scarlet fever, rheumatic fever, and acute glomerulonephritis. Lastly, but most interestingly, the Strep family includes Streptococcus pyogenes, the bacterium most infamously known as the flesh-eating bacteria that causes a most terrifying disease known as necrotizing fasciitis.
What I find most remarkable, though, is the surprise with which we meet the discovery that this horrifying microbe is not an exotic, tropical disease agent, but rather, it lives in our own backyards: on our skin. It’s not a swarm of migrating killer bees, or a particularly nasty species of fire ant stowing aboard a ship from the South Pacific. It’s just an everyday, common, garden-variety bacteria. My colleagues who have not read Atul Gawanade’s Complications or watched that episode of House, M.D. featuring what my girlfriend’s classmates affectionately call “nec fasc” (pronounced “neck-fash”) seemed alarmed by the notion that such a common bacterium could cause a disease that sounds like it came from a 1950’s horror film. Similarly, when cases of necrotizing fasciitis appear in hospitals, the popular media is often quick to jump on the latest scare with the same, strange avidity with which Hollywood has produced sequels to I Know What You Did Last Summer (I Still Know What You Did Last Summer,I’ll Always Know What You Did Last Summer…).
Now, we can be repeatedly suckered into the popular media’s (at best, ignorant) scare tactics every time a case of necrotizing fasciitis shows up, or we can actually learn something about this disease. A few pointers:
1. In NF, the bacteria infect the “fascia” or connective tissue beneath the skin, causing damage and the closure of blood vessels. The muscles and other tissue supplied by those blood vessels become ischemic (lose their oxygen and nutrient supply) and necrotic (cells start dying). While the bacteria spread through the connective tissue under the skin, certain components of the multi-faceted immune system are triggered by the infection and cause further damage to the surrounding tissue while the bacteria manage survive the attack with special protective mechanisms that inhibit the immune system components that might otherwise defeat the bacteria. The severe, sometimes fatal infection can spread quickly, within hours or days, and may have a mortality of rate of between 25-30%. NF may begin with any breakage of the skin (cut, scrape, surgical procedure, etc.) or through other unknown mechanisms.
2. Necrotizing fasciitis is a rare disease according to the Office of Rare Diseases at the NIH (National Institutes of Health), meaning it affects less than 1 in 200,000 individuals in the U.S.
3. Necrotizing fasciitis is usually caused by S. pyogenes, but may be caused by other bacteria or combinations of bacteria. These bacteria are often normal inhabitants on or in our bodies. It’s speculated that NF cases tend to occur when either:
(a) the patient is immunocompromised, such as with glucocorticoid treatments, immune deficiency diseases, immunosuppressant treatments, prior infections, or chronic diseases such as diabetes mellitus.
(b) or the bacteria on the skin interact with anaerobic (non-oxygen-requiring) bacteria, possibly swapping traits that allow one or the other bacteria to spread more readily and escape the immune defenses.
4. Again, necroticizing fasciitis is a RARE disease. However, if you or someone else is having a fever, chills, and a rapidly spreading, red swelling (aka erythema) (and/or other symptoms), it’s worth having it checked immediately by a physician. Catching and treating the infection early is very important for improving the patient’s prognosis.
This makes me wonder why there seems to be no such thing as “urgent” or “emergency care” in dermatology (though I suppose these extreme skin infections are thus treated in Emergency Departments, Medicine wards, and Operating Rooms). Which reminds me of an episode of Scrubs:
J.D.: “You see a lot of sad things in a hospital, but nothing’s quite as sad as a dermatologist that’s just been paged, milking it for all it’s worth.”
Dermatologist: “Alright everybody! Watch your backs! Skin doctor coming through! I gotta get somewhere! STAT!”
1. MedlinePlus Medical Encyclopedia: Necrotizing soft tissue infection