Necrotizing Fasciitis (cont.)
Do different types of necrotizing fasciitis exist?
Variations of necrotizing fasciitis are placed by some investigators into three general groups, roughly based on the genera of organisms causing the infection and some clinical findings that unfortunately vary from patient to patient. Type 1 is either caused by more than two bacterial genera (polymicrobial) or by the infrequently found single bacterial genus such as
Vibrio or fungal genera such as Candida. Type 2 is caused by Streptococcus spp, and
type 3 (or termed type 3 gas gangrene) is caused by
Clostridium spp. One example of clinical findings (gas in tissues) is more often found in
type 3, but can be found in types 1 and 2 also. Many investigators elect not to use this typing system and simply identify the organism(s) causing the necrotizing fasciitis.
What causes necrotizing fasciitis?
Most cases of necrotizing fasciitis are caused by bacteria; only rarely do other organisms such as fungi cause this disease. Group A
Streptococci and Staphylococci, either alone or with other bacteria, cause many cases of necrotizing fasciitis, although
Clostridium spp should be considered as a cause especially if gas is found in the infected tissue. Because of better microbial isolation techniques for anaerobic bacteria, bacterial genera such as
Bacteroides, Peptostreptococcus, and Clostridium are often cultured from the infected area. Frequently, culture of tissue involved by necrotizing fasciitis also yields a mixture of other
non-anaerobic bacterial genera such as
E. coli, Klebsiella, Pseudomonas, and others. Many investigators conclude that
non-anaerobic organisms damage tissue areas enough to cause local areas of hypoxia (reduced oxygen) where anaerobic organisms then can thrive and extend the infection further. This results in polymicrobial infection in which one type of bacteria aids the survival and growth of another type of bacteria (synergy). Infrequently,
Vibrio vulnificus causes the disease when a person, usually someone with liver function problems (for
example, alcoholics or immunosuppressed patients), eats contaminated seafood or a wound gets contaminated with seawater containing
Vibrio vulnificus.
In general, the bacteria that cause necrotizing fasciitis utilize similar methods to cause and advance the disease. Most produce toxins that inhibit the immune response, damage or kill tissue, produce tissue hypoxia, specifically dissolve connective tissue, or do all of the above. In polymicrobic infections, one bacterial genus may produce one toxic factor (for
example,
E. coli causing tissue hypoxia) while different types of coinfecting bacteria may produce other toxins that lyse
(disintegrate) damaged tissue cells or connective tissue.
Next: What are the symptoms of necrotizing fasciitis? »
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