When Bacteria Go Bad - the Case of Necrotizing Fasciitis
Flesh-eating disease. it sounds like the stuff of science fiction. It can spread through human tissue at a rate of 3 cm per hour. Twenty-five percent of its victims die, and in severe cases, the patient is dead within 18 hours. In 1990, it caused the death of Muppets creator, Jim Henson. It is small wonder that the media has given the disease such a dramatic, horrible-sounding name.
Unfortunately, this is not an excerpt from a science fiction novel, but rather a chapter from a bacteriology textbook. The medical name for this disease is necrotizing fasciitis (NF) and it is caused by a bacterium called Streptococcus pyogenes, or Group A streptococcus (GAS).
In 1871, a Confederate army surgeon named Joseph Jones first described the disease during the Civil War. By 1918, the cause of the disease was identified as a bacterial infection. It was named "necrotizing fasciitis" in 1952, from necrosis, which means death of a portion of tissue, and fascia, which refers to the fibrous tissues that enclose and connect the muscles.
Throughout the 19th and 20th centuries, cases of NF occurred only sporadically and usually remained restricted to military hospitals during wartime, although some civilian population outbreaks have also occurred. The Centers for Disease Control and Prevention (CDC) reports that, worldwide, rates of NF increased from the mid-1980s to early 1990s. Increases in the rate and severity of NF are associated with increases in the prevalence of toxin-producing strains of S. pyogenes (M-1 and M-3 serotypes). In 1999, approximately 600 cases of NF were reported in the United States, according to the CDC.
Streptococcus pyogenes, or Group A Streptococcus (GAS)
This bacterium is a spherical cell with a diameter of 0.6-1.0 mm.It thrives in pairs or short chains and can be grown in the laboratory in blood or human serum. People often carry GAS in their throats or on their skin but exhibit no symptoms of illness. S. pyogenes is also responsible for diseases like strep throat, rheumatic fever, scarlet fever, and skin infections like impetigo. These infections are referred to as "non-invasive GAS disease." More than 10 million non-invasive GAS infections (mostly throat and skin infections) occur annually. Sometimes GAS can travel to parts of the body where bacteria usually are not found (blood, muscles, or the lungs). The resulting infections are referred to as "invasive GAS disease." One of the least common, but most severe forms of invasive GAS disease is NF. The CDC reports that about 9,400 cases (3.5/100,000 population) of invasive GAS disease occurred in the US in 1999. Of these, approximately 6%, or 600, were identified as NF.
Scientists are puzzled as to why the normally mild GAS bacteria can sometimes become deadly, as in the case of NF. Invasive GAS infections may occur when the bacterium bypasses a person's normal defenses and enters the tissue through sores or openings in the skin. Also, the more virulent strains of GAS are more likely to cause severe diseases. Since a bacterium's generation time may be as short as 20 minutes, these organisms can evolve quickly. Many scientists believe that GAS has evolved to make proteins that cause the body's immune system to destroy the body's tissues directly. Thus, by trying to fight the bacteria, the body destroys itself.
Progress of Necrotizing Fasciitis
The National Institute of Allergy and Infectious Diseases defines NF as "a serious but rare infection of the deeper layers of skin and fatty subcutaneous tissues (fascia)." Eventually, NF destroys not only muscle, but also fat and skin tissue.
The disease does not begin as a sore throat. A minor trauma in an extremity, such as a small cut, bruise, or the chicken pox, becomes infected and is the most usual beginning to NF. Some cases also occur after surgeries, including abdominal surgeries and cesarean deliveries, or after vaginal births. The bacterium attacks soft subcutaneous tissue and causes it to become gangrenous. The infection spreads under the skin where it is unobservable. It can move up the affected body part at a rate of three cm per hour. When subsequent necrosis (death) of subcutaneous tissue occurs, the tissue must be removed surgically. The bacteria also causes the body to go into systemic shock, which may lead to renal failure, low blood pressure, respiratory failure, and heart failure. In severe cases, death may occur within 18 hours.
The symptoms of NF are similar to influenza. The following symptoms of NF were compiled from the Center for Disease Control and Prevention and the National Necrotizing Fasciitis Foundation:
* Minor trauma
* Affected skin becomes red/violet, hot and swollen
* Very severe pain beyond what you would expect from the type of wound or injury
* Flu-like symptoms: fever, weakness, vomiting, diarrhea, dehydration
* Condition worsens without any improvement
* Less frequent urination
* Possibility of a sunburn-type rash
* Possibility of large, dark boil-like blister(s)
* Possibility of shock
Risks of Contacting Invasive Group A Streptococcal Disease
GAS is a common bacterium. In fact, 10-15% of school age children may carry GAS in their throats and display no symptoms. GAS spreads by direct contact with infected skin lesions or with nose or throat discharges from an infected person. Normally, GAS is passed by close personal contact such as kissing and sharing eating utensils or cigarettes. Although GAS is passed from person to person, NF itself is not contagious. Few people who come in contact with GAS will develop invasive GAS disease. The CDC warns that those with a higher risk of contacting the disease are people with chronic illnesses like cancer, diabetes, and kidney diseases requiring dialysis, and those who use medications such as steroids. Breaks in the skin, such as cuts, surgical wounds, and chicken pox increase the chance of bacteria entering the body.
PreventionThe following is a list of recommendations to prevent the disease, as reported by the CDC.
* Good hand washing can prevent the spread of GAS infection, especially after coughing, sneezing and before preparing food or eating.
* Patients with sore throats should be seen by a doctor.
* Patients with strep throat should stay home until 24 hours after their last antiobiotic dose.
* Keeping the skin intact is important.
* Wounds should be cleaned and monitored for signs of infection (redness, swelling, drainage, pain).
* Keeping the skin intact is an important factor in preventing NF.
* Patients with an infected wound and fever should seek medical care.
No vaccine is available to prevent GAS infections. Since many types of GAS exist, one of the challenges facing scientists is the development of one vaccine to combat all the different types. Early diagnosis and early medical treatment are the keys to surviving NF. Blood or pus cultures can be used to diagnose NF, and treatment includes intravenous antibiotics (penicillin and clindamycin) and aggressive surgical debridement (removal of infected tissue). Surgical intervention can range from removing flesh, subcutaneous tissue, and fat in early stages, to major limb amputation in advanced stages. The combination of early diagnosis, antibiotics, and surgery is usually sufficient to save patients' lives.
More than 80 variants of GAS exist, and each type produces its own unique proteins. Specific GAS syndromes are caused by some of these proteins. Researchers have now determined the genetic sequence for more than 95% of the GAS organisms in hopes of identifying the proteins causing virulence. This information may lead to new and improved drugs and vaccines. Additionally, the CDC has also developed a new genotyping system for GAS isolates (emm typing) that improves strain identification. Both epidemiologists and improved surveillance of the disease will also help to identify trends and groups at risk. This information may lead to new and improved drugs and vaccines.
With further advances in medical research, "flesh eating disease" may be able to move from the pages of science fiction and bacteriology into the pages of ancient history.
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