Necrotizing Fasciitis (Flesh-Eating Disease)

Necrotizing Fasciitis (Flesh-Eating Disease) Overview

Necrotizing fasciitis (NF) is a rapidly progressive infection that primarily affects the subcutaneous connective tissue planes (fascia), where it may quickly spread to involve adjacent soft tissue, leading to widespread necrosis (tissue death). Several different types of flesh-eating bacteria may cause this life-threatening condition, which can affect both healthy individuals as well as those with underlying medical problems. Though rarely encountered, there has been an increase in the incidence of necrotizing fasciitis over the last few decades. It is estimated that there are between 500-1,000 cases of necrotizing fasciitis in the United States each year. Early identification and prompt treatment of necrotizing fasciitis is critical to manage the potentially devastating consequences of this medical emergency.

History of Necrotizing Fasciitis

Though necrotizing fasciitis has likely existed for many centuries, several detailed descriptions of this condition were reported in the 1800s. In 1952, Dr. B. Wilson first used the term necrotizing fasciitis to describe this condition, and this term has remained the most commonly used in modern medicine. Other terms that have been used to describe this same condition include flesh-eating bacteria syndrome, suppurative fasciitis, necrotizing cellulitis, necrotizing soft tissue infection, hospital gangrene, streptococcal gangrene, dermal gangrene, Meleney's ulcer, and Meleney's gangrene. When necrotizing fasciitis affects the genital area, it is often referred to as Fournier gangrene (also termed Fournier's gangrene).

Necrotizing Fasciitis Causes

Necrotizing fasciitis is caused by bacteria in the vast majority of cases, though fungi can also rarely lead to this condition as well. Many cases of necrotizing fasciitis are caused by group A beta-hemolytic streptococci (Streptococcus pyogenes), either individually or along with other bacterial pathogens. Group A streptococcus is the same bacteria responsible for "strep throat," impetigo (skin infection), and rheumatic fever. In recent years, there has been a surge in cases of necrotizing fasciitis caused by community-acquired methicillin-resistant Staphylococcus aureus (MRSA), often occurring in intravenous drug abusers. Most cases of necrotizing fasciitis are polymicrobial and involve both aerobic and anaerobic bacteria. Additional bacterial organisms that may be isolated in cases of necrotizing fasciitis include Escherichia coli, Klebsiella, Pseudomonas, Proteus, Vibrio, Bacteroides, Peptostreptococcus, and Clostridium, among others. A rarely encountered bacterium in humans, Aeromonas hydrophila has recently been implicated in a case of necrotizing fasciitis in a young female who cut her leg in a zip line accident. This organism, generally found in freshwater and brackish water in warmer climates, typically causes infections in fish and amphibians.
In many cases of necrotizing fasciitis, there is a history of prior trauma, such as a cut, scrape, insect bite, burn, or needle puncture wound. These lesions may initially appear trivial or minor. Surgical incision sites and various surgical procedures may also serve as a source of infection. In many cases, however, there is no obvious source of infection or portal of entry to explain the cause (idiopathic).
After the bacterial pathogen gains entry, the infection can spread from the subcutaneous tissues to involve deeper facial planes. Progressive spread of the infection will ensue, and it can sometimes involve adjacent soft tissues as well, including muscle, fat, and skin. Various bacterial enzymes and toxins lead to vascular occlusion, resulting in tissue hypoxia (decreased oxygen) and ultimately tissue necrosis. In many cases, these tissue conditions allow anaerobic bacteria to proliferate as well, allowing for the progressive spread of infection and continued destruction of tissue.
Individuals with underlying medical problems and a weakened immune system are also at increased risk of developing necrotizing fasciitis. Various medical conditions, including diabetes, renal failure, liver disease, cancer, peripheral vascular disease, and HIV infection, are often present in patients who develop necrotizing fasciitis, as are individuals undergoing chemotherapy and those taking corticosteroids for various reasons. Alcoholics and intravenous-drug abusers are also at increased risk. Many cases of necrotizing fasciitis, however, also occur in otherwise healthy individuals with no predisposing factors.
For classification purposes, necrotizing fasciitis has been subdivided into three distinct groupings, primarily based on the microbiology of the underlying infection; type 1 NF is caused by multiple bacterial species (polymicrobial), type 2 NF is caused by a single bacterial species (monomicrobial) which is typically Streptococcus pyogenes, and type 3 NF (gas gangrene) is caused by Clostridium spp. Infection caused by Vibrio spp (frequently Vibrio vulnificus) is a variant form often occurring in individuals with liver disease, typically after ingesting seafood or exposing skin wounds to seawater contaminated by this organism.

Necrotizing Fasciitis Symptoms and Signs

The symptoms and signs of necrotizing fasciitis vary with the extent and progression of the disease. Necrotizing fasciitis often affects the extremities or the genital area (Fournier's gangrene), though any area of the body may be involved.
Early in the course of the disease, patients with necrotizing fasciitis may initially appear deceptively well, and they may not demonstrate any superficial visible signs of an underlying infection. Some individuals may initially complain of pain or soreness, similar to that of a "pulled muscle." However as the infection rapidly spreads, the symptoms and signs of severe illness become apparent.
Necrotizing fasciitis generally appears as an area of localized redness, warmth, swelling, and pain, often resembling a superficial skin infection (cellulitis). Many times, the pain and tenderness experienced by patients is out of proportion to the visible findings on the skin. Fever and chills may be present. Over the course of hours to days, the redness of the skin rapidly spreads and the skin may become dusky, purplish, or dark in color. Overlying blisters, necrotic eschars (black scabs), hardening of the skin (induration), skin breakdown, and wound drainage may develop. Sometimes a fine crackling sensation may be felt under the skin (crepitus), signifying gas within the tissues. The severe pain and tenderness experienced may later diminish because of subsequent nerve damage, leading to localized anesthesia of the affected area. If left untreated, continued spread of the infection and widespread bodily involvement invariably occurs, frequently leading to sepsis (spread of the infection to the bloodstream) and often death.
Other associated symptoms seen with necrotizing fasciitis may include malaise, nausea, vomiting, weakness, dizziness, and confusion.

When to Seek Medical Care

Prompt identification and treatment of necrotizing fasciitis is critical in order to improve the likelihood of a favorable outcome. Because of the rapid progression of this condition, a high index of suspicion and early detection are necessary to initiate emergency treatment immediately. Those individuals with underlying medical problems or a weakened immune system need to be especially vigilant. Consult a health care professional if any of the following symptoms or signs develops:

• An unexplained area of skin redness, warmth, tenderness or swelling, associated with or without a history of antecedent skin trauma
• Changes in the color of the skin (dusky, purple, mottled, black) or in the texture of the skin (blisters, open wounds, hardening, crepitus)
• Drainage from any open wound
• Fever or chills
• Intense pain or discomfort of a body area associated with or without prior trauma

If a person has been previously evaluated by a health care professional and there is progression of the above symptoms, or if the person fails to improve (even with antibiotic treatment at home), prompt reevaluation must occur.