The infected skin is red, warm to the touch, and sometimes swollen, and gas bubbles may form under the skin.
The person usually has intense pain, feels very ill, and has a high fever.
The diagnosis is based on a doctor's evaluation, x-rays, and laboratory tests.
Treatment involves removing dead skin, which sometimes requires extensive surgery, and giving intravenous antibiotics.
(See also Overview of Bacterial Skin Infections.)
Most skin infections do not result in the death of skin and nearby tissues. Sometimes, however, bacterial infection can cause small blood vessels in the infected area to clot. This clotting causes the tissue fed by these vessels to die from lack of blood. Dead tissue is termed necrotic. Because the body's immune defenses that travel through the bloodstream (such as white blood cells and antibodies) can no longer reach this area, the infection spreads rapidly and may be difficult to control. Death can occur, even with appropriate treatment.
Some necrotizing skin infections spread deep in the skin along the surface of the connective tissue that covers muscle (fascia) and are termed necrotizing fasciitis. Other necrotizing skin infections spread in the outer layers of skin and are termed necrotizing cellulitis. Several different bacteria, such as Streptococcus and Clostridia, may cause necrotizing skin infections, but in many people the infections are caused by a combination of bacteria. The necrotizing skin infection caused by streptococci in particular has been termed “flesh-eating disease” by the lay press, but it differs little from the others.
Some necrotizing skin infections begin at puncture wounds or lacerations, particularly wounds contaminated with dirt and debris. Other infections begin in surgical incisions or even healthy skin. Sometimes people with diverticulitis, intestinal perforation, or tumors of the intestine develop necrotizing infections of the abdominal wall, genital area, or thighs. These infections occur when certain bacteria escape from the intestine and spread to the skin. The bacteria may initially create an abscess (a pocket of pus) in the abdominal cavity and spread directly outward to the skin, or they may spread through the bloodstream to the skin and other organs. People with diabetes are at particular risk of necrotizing skin infections.
Symptoms of necrotizing skin infections often begin just as for a common skin infection,cellulitis. The skin may look pale at first but quickly becomes red or bronze and warm to the touch and sometimes swollen. Later, the skin turns violet, often with the development of large fluid-filled blisters (bullae). The fluid from these blisters is brown, watery, and sometimes foul smelling. Areas of dead skin turn black (gangrene). Some types of infection, including those caused by Clostridia and mixed bacteria, produce gas. The gas creates bubbles under the skin and sometimes in the blisters themselves, causing the skin to feel crackly when pressed. Initially the infected area is extremely painful, but as the skin dies, the nerves stop working and the area loses sensation. The muscles may be affected as the infection worsens.
The person usually feels very ill and has a high fever, a rapid heart rate, and mental deterioration ranging from confusion to unconsciousness. Blood pressure may fall because of toxins secreted by the bacteria and the body’s response to the infection (septic shock). People may develop toxic shock syndrome.
A doctor makes a diagnosis of necrotizing skin infection based on its appearance, particularly the presence of gas bubbles under the skin. X-rays may show gas under the skin as well.
A blood test usually shows that the number of white blood cells has increased (leukocytosis). The specific bacteria causing the infection are identified by laboratory analysis of blood or tissue samples (culture). However, doctors begin treatment before they have the laboratory test results.
The treatment of necrotizing fasciitis is surgical removal of the dead tissue plus antibiotics given by vein (intravenously). Large amounts of skin, tissue, and muscle must often be removed, and in some cases, an affected arm or leg may have to be removed (amputated).
People may need large volumes of intravenous fluids before and after surgery. Some doctors recommend treatment in a high-pressure (hyperbaric) oxygen chamber, but it is not clear how much this helps. People who also develop toxic shock syndrome may be given intravenous immune globulin.