Clostridial gas gangrene is a highly lethal necrotizing soft tissue infection of skeletal muscle caused by toxin- and gas-producing Clostridium species. The synonym clostridial myonecrosis better describes both the causative agent and the target tissue. Prior to the advent of antibiotics and mobile army surgical hospitals, as many as 5% of battlefield injuries were complicated by this condition. However, the incidence rate dropped to less than 0.01% during the Vietnam War. Presently, 90% of contaminated wounds demonstrate clostridial organisms, but fewer than 2% develop clostridial myonecrosis. This underscores the importance of host and local wound factors in the development of this process, rather than the mere presence of the organisms in the wound.
Clostridial myonecrosis may also occur following surgery, most often of the gastrointestinal or biliary tract, and following septic abortions.  Clostridium perfringens, Clostridium septicum, and Clostridium histolyticum are the principal causes of trauma-associated gas gangrene, and their incidence increases dramatically in times of war, hurricanes, earthquakes, and other mass-casualty conditions. There has also been an increased incidence of spontaneous gas gangrene caused by C septicum in association with gastrointestinal abnormalities and neutropenia. 
Similarly, over the last 15 years, a toxic shock–like syndrome associated with Clostridium sordellii infection has been increasingly recognized in individuals skin-popping black tar heroin and in women undergoing childbirth or other gynecologic procedures, including medically induced abortion. 
Clostridia are gram-positive, anaerobic, spore-forming bacilli commonly found throughout nature (with the exception of the North African desert). Cultivated rich soil has the highest density of organisms. In addition, clostridia have been isolated from normal human colonic flora, skin, and the vagina. More than 150 Clostridium species have been identified, but only 6 have been demonstrated to be capable of producing the fulminant condition known as clostridial gas gangrene. Usually, more than 1 species is isolated from clinical specimens. A study by Mendez et al suggests that sugar may inhibit the production of alpha and theta toxins that trigger the gas. 
Clostridium perfringens, previously known as Clostridium welchii, is the most common cause of clostridial gas gangrene (80-90% of cases). Other clostridia species responsible for the condition include Clostridium novyi (40%), Clostridium septicum (20%), Clostridium histolyticum (10%), Clostridium bifermentans (10%), and Clostridium fallax (5%).
Infections are characterized by a very low level of host inflammation in response to organism-associated exotoxins. In fact, it is more of a response to the exotoxins than a classic immune response to invading organisms. Purulence is often absent. The process of myonecrosis can spread as fast as 2 cm/h. This results in systemic toxicity and shock that can be fatal within 12 hours. Overwhelming shock with accompanying renal failure usually leads to death.
Infection requires 2 conditions to coexist. First, organisms must be inoculated into the tissues. Second, oxygen tension must be low enough for the organisms to proliferate. These organisms are not strict anaerobes; 30% oxygen tension in the tissues allows for free growth of these bacteria, but 70% oxygen tension restricts their growth. Inoculation of organisms into low oxygen tension tissues is followed by an incubation period that usually ranges from 12-24 hours. However, this period can be as brief as 1 hour or as long as several weeks. The organisms then multiply and produce exotoxins that result in myonecrosis.
Although not very well understood, exotoxins appear to be tissue-destructive soluble antigens produced by clostridia. They include lecithinase, collagenase, hyaluronidase, fibrinolysin, hemagglutinin, and hemolysin toxins. C perfringens produces at least 17 identifiable exotoxins that are used for species typing (eg, type A, type B, type C).
Theta toxin causes direct vascular injury, cytolysis, hemolysis, leukocyte degeneration, and polymorphonuclear cell destruction. These effects on leukocytes may explain the relatively minor host inflammatory response that is observed in tissues of patients with clostridial myonecrosis.
Kappa toxin, also produced by C perfringens, is a collagenase that facilitates the rapid spread of necrosis through tissue planes by destroying connective tissue.
Alpha toxin is produced by most clostridia and has phospholipase C activity. This potent lecithinase causes lysis of red blood cells, myocytes, fibroblasts, platelets, and leukocytes. It also may decrease cardiac inotropy and trigger histamine release, platelet aggregation, and thrombus formation. 
Approximately 1000 cases of clostridial gas gangrene are reported per year.
Although no published data exist, prevalence is most likely higher in countries other than the United States because of lack of access to health care in other parts of the world.
If properly treated, the overall mortality rate is 20%-30%. If untreated, the process is 100% fatal.
Spontaneous cases carry a mortality rate of 67-100%.
With trunk involvement, the mortality rate is higher (60%) than the mortality rate associated with involvement of the extremities, which carries a better prognosis.
A longer incubation period, presence of significant comorbidities, and development of shock increase the risk of mortality.
No race predilection exists.
No sex predilection exists.
Age does not seem to be an independent risk factor. However, because elderly individuals more often have significant comorbidities, they are at higher risk for mortality than younger patients.
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