Necrotizing fasciitis is a progressive infection that causes necrosis (death) of the fascia-the fibrous connective membranes overlying muscle and other soft tissue-and can be fatal. Although it is an "old" and uncommon disease, it has received publicity recently and been called "flesh-eating bacteria." In most cases, the infection is caused by a bacterium called group A streptococcus.
Who's at Risk?
Necrotizing fasciitis, a relatively rare infection, occurs most commonly in those with weakened immune functioning. Conditions that increase a person's risk include diabetes, obesity, cancer, malnutrition, alcoholism, immunosuppressive therapy (such as steroids), and peripheral vascular disease. Advanced age is another risk factor. In addition, some cases of necrotizing fasciitis have occurred in the aftermath of a number of OB-GYN procedures, namely:
- cesarean delivery;
- episiotomy (incision in the perineum) and pudendal nerve blocks-both procedures are used to ease childbirth;
- hysterectomy; and
- tubal ligation.
Most commonly, necrotizing fasciitis develops in the abdominal wall, extremities (arms and legs), and perineum (the area between the vagina and rectum). In women, the infection typically begins in the vulva, then spreads to the perineum, buttocks, and abdominal wall.
The majority of necrotizing fasciitis cases of the vulva occurs in obese, diabetic women. However, there are reported cases in younger women following childbirth, as a consequence of episiotomy or pudendal nerve blocks, procedures used to ease delivery. Infections of the abdominal wall usually follow abdominal surgery. This commonly occurs when the area being operated on becomes contaminated due to trauma or if the contents of the bowel spill into the abdominal cavity. Necrotizing fasciitis has also developed in the aftermath of cesarean delivery, hysterectomy, tubal ligation, and laparoscopy.
This infectious organism may invade the affected area in a number of ways:
- directly through the skin;
- spreading from surrounding structures like the bladder or rectum; or
- as a complication of catheters or drains placed through the skin.
When this infection involves the arms or legs, it typically follows an injury, intravenous drug use, or an insect bite. At any site on the body, it may develop from an unrecognized scratch or ulcer.
Cases of necrotizing fasciitis have been categorized into two distinct groups, based on the type of bacteria isolated. Organisms that live in water cause a third type of necrotizing fasciitis.
- Type 1 is caused by two or more bacteria, including aerobes (bacteria that need oxygen to survive), anaerobes (bacteria that grow well in the absence of oxygen), and/or facultative anaerobes (bacteria that can grow in a reduced oxygen environment). Anaerobes are never the sole organism. Abdominal and perineal infections tend to be Type 1.
- Type 2 is caused by group A b -hemolytic streptococci bacteria ( Streptococcus pyogenes ), alone or in combination with staphylococci species. This type has been previously known as hemolytic streptococcal gangrene. Lesions of the extremities are more commonly Type 2, as are cases of necrotizing fasciitis occurring in previously healthy young patients.
- Type 3 necrotizing fasciitis is caused by marine vibrios (organisms that live in water). Vibrio species are usually identified following a puncture wound or bite from a fish or shellfish. Pathogenic vibrio species cause a rapidly progressive soft tissue necrosis. They are believed to synthesize a substance called an extracellular toxin that worsens the soft tissue damage. Moreover, vibrio species are gram-negative bacteria (have a double membrane surrounding each cell). This makes them tougher to kill and more resistant to antibiotics.
As noted, necrotizing fasciitis is a progressive, often fatal, infection. Unfortunately, there may be no outward sign of the infection until it has progressed considerably. When skin changes are apparent, they reflect only a small amount of the underlying damage done to the fibrous membrane below the skin. There is likely to be extensive swelling and pain over the affected area. Discoloration is also likely; the skin may become reddish purple, then blue or brown. Blister-like areas may form, and grayish, foul-smelling fluid may seep from the skin. The skin may slip over the underlying tissue. Pressing on the affected area causes a crackling sound (crepitus), caused by the collection of gases underneath the skin. In four or five days, the skin may become gangrenous (yellow). As the tissue is destroyed, so are the nerves within it, and the area that was previously painful becomes numb. The skin may slough (separate from the underlying tissue) spontaneously if left untreated.
As the bacteria and toxins enter the bloodstream, the patient becomes very sick and may develop electrolyte abnormalities and low blood pressure. The bacteria may break down red blood cells, causing anemia. Bleeding disorders may also occur. In the absence of prompt, aggressive treatment, essentially all patients die. Even with proper treatment, the mortality rate may be as high as 30 to 75%.
It can be difficult for your doctor to diagnose necrotizing fasciitis. As noted, your skin may appear normal early in the course of the infection, with no obvious swelling or tenderness. If you have pain that is more severe than expected based on any obvious outward sign or if you are very ill, you may have a progressing infection.
If it is a clear-cut case or if it is highly probable that you have this infection and your illness is worsening, additional testing is unnecessary, since it is usually inconclusive and merely delays treatment. The best way for your doctor to confirm diagnosis and initiate treatment is to open the area surgically and obtain a biopsy and gram stain. In this procedure, your doctor takes a sample of the bacteria, applies a dye, and views the bacteria under a microscope. The gram stain is valuable in ruling out less common causes, such as clostridial organisms, vibrio species, or fungal organisms.
For some cases, various diagnostic procedures may be useful.
- X-rays may detect soft tissue gas not identified on physical examination.
- CT (computed tomography) scanning is more accurate in detecting soft tissue gas and may be useful in determining the extent of spread.
- (magnetic resonance imaging), in addition to identifying soft tissue gas, may be able to determine good tissue from bad tissue.
- Ultrasound may help to exclude other conditions, such as an abscess (pus collection), especially in the pelvic area.
A diagnosis of necrotizing fasciitis is a medical emergency. You require treatment in an intensive care unit. This is necessary so that your condition can be monitored closely. Some patients require a ventilator or special nutritional support. You are treated with antibiotics. Antibiotics with broad coverage (effective against many organisms) are administered until the specific bacteria involved are identified. Once the bacteria are identified, the antibiotics are modified as needed. If a fungal infection is identified, special treatment with antifungal agents is started. You also receive a tetanus vaccination because Clostridium tetani, the bacteria that causes tetanus, may be the cause.
Extensive surgical removal of all necrotic tissue is necessary to cure this infection. The necrotic tissue typically reaches beyond the boundaries of affected areas of the skin. The affected tissue does not bleed and usually leaks a grayish "dishwater-like" fluid, while healthy tissue appears bright yellow and bloody in comparison. There may be finger-like projections of necrotic tissue extending into normal tissue-these must be removed as well. Sometimes, surgery is radical because your surgeon tries to remove all the tissue. But, because this is difficult to do, you may require two or more major operations under general anesthesia. After surgery, the wound is left open so that it can be examined frequently. Gauze and saline dressings are changed often. Fortunately, most wounds eventually close.
After surgery, you may be given therapy with hyperbaric (high-pressure) oxygen. This may help improve wound healing, although it has not been shown to improve survival. Your doctor may recommend reconstructive surgery after the infection has cleared.