Risk factors More than 70% of cases are recorded in people with at least one of these clinical situations: immunosuppression, diabetes, alcoholism/drug abuse/smoking, malignancies, and chronic systemic diseases. For reasons that are unclear, it occasionally occurs in people with an apparently normal general condition.<unk>  can occur at any part of the body, but it is more commonly seen at the extremities, perineum, and genitals. Only a few of such cases arise from the chest and abdomen. Trauma is the usual cause of the infection, such as from intravenous drug injection, insulin injection, animal and insect bites, catheter insertion over the skin, or a fistula connecting skin to the internal body organs. Skin infections such as abscess and ulcers can also complicate<unk> . Spreading of infection through blood has been suggested for those with streptococcal pharyngitis. For infection of the perineum and genitals (Fournier gangrene), trauma, surgery, urinary tract infection, stones, and Bartholin gland abscess are the usual causes. The risk of developing<unk>  from a wound can be reduced by good wound care and handwashing. Bacteria Types of soft-tissue<unk>  infection can be divided into four classes according to the types of bacteria infecting the soft tissue. This classification system was first described by Giuliano and his colleagues in 1977. Type I infection: This is the most common type of infection, and accounts for 70 to 80% of cases. It is caused by a mixture of bacterial types, usually in abdominal or groin areas. This type of infection is usually caused by various species of Gram-positive cocci, (Staphylococcus aureus, Streptococcus pyogenes, and enterococci), Gram-negative rods, (Escherichia coli, Pseudomonas aeruginosa), and anaerobes, (Bacteroides and Clostridium species). Populations of those affected are typically older with medical comorbidities such as diabetes mellitus, obesity, and immunodeficiency. Usually, trauma is not the cause of such infections. Previous history of abscess infection or gut perforation with bacterial translocation may be elicited. Clostridial infection accounts for 10% of type I infection. Clostridium species involved are Clostridium perfringens, Clostridium septicum, and Clostridium sordellii, which typically cause gas gangrene (also known as myonecrosis). Clostridium perfringens produces two deadly toxins: alpha-toxin and theta-toxin. Alpha-toxin causes excessive platelet aggregation which blocks blood vessels and deprives the vital organs of oxygen supply. This creates an acidic, oxygen-deficient environment for the proliferation of bacteria. When alpha-toxin is absorbed by soft tissues, it can inhibit the migration of white blood cells from blood vessels into the soft tissue, thus impairing phagocyte function. The two toxins together can cause destruction of red blood cells in blood vessels, damage to the integrity of the blood vessels, and suppression of heart function. Clostridium sordellii can also produce two major toxins: all known virulent strains produce the essential virulence factor lethal toxin (TcsL), and a number also produce haemorrhagic toxin (TcsH). TcsL and TcsH are both members of the large clostridial cytotoxin (LCC) family. The key Clostridium septicum virulence factor is a pore-forming toxin called alpha-toxin, though it is unrelated to the Clostridium perfringens alpha-toxin. Myonecrotic infections caused by these clostridial species commonly occur in injecting heroin users. Those with clostridial infections typically have severe pain at the wound site, where the wound typically drains foul-smelling blood mixed with serum (serosanguinous discharge). Shock can progress rapidly after initial injury or infection, and once the state of shock is established, the chance of dying exceeds 50%. Another bacterium associated with similar rapid disease progression is group A streptococcal infection (mostly Streptococcus pyogenes). Meanwhile, other bacterial infections require two or more days to become symptomatic. Type II infection: This infection accounts for 20 to 30% of cases, mainly involving the extremities. This mainly involves Streptococcus pyogenes bacteria, alone or in combination with staphylococcal infections. Both types of bacteria can progress rapidly and manifest as toxic shock syndrome. Streptococcus species produce M protein, which acts as a superantigen, stimulating a massive systemic immune response which is not effective against the bacterial antigen, precipitating shock. Type II infection more commonly affects young, healthy adults with a history of injury. Type III infection: Vibrio vulnificus, a bacterium found in saltwater, is a rare cause of this infection, which occurs through a break in the skin. Disease progression is similar to type II but sometimes with little visible skin changes. Type IV infection: Some authors have described the type IV infection as fungal in nature.
Necrotizing fasciitis
Cellulitis
Ischemic fasciitis
Gas gangrene
Pyomyositis
Plantar fasciitis
Fournier gangrene
Abscess