What Is Erysipelas (St. Anthony's Fire)?

Erysipelas is an infection of the outer layers of skin caused by a bacterium called Streptococcus pyogenes. Symptoms include pain, redness, and rash and, often, fever, chills, and malaise. Erysipelas also can cause swelling and blockage of the superficial vessels of the lymphatic system. Although potentially serious, erysipelas usually can be treated with antibiotics.

Erysipelas is sometimes referred to as St. Anthony's Fire because of the fiery appearance of the rash. Erysipelas was identified as far back as the 11th century, where it and a cluster of other diseases were collectively named after Saint Anthony, the patron saint of lost causes.

Symptoms of Erysipelas

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Erysipelas is characterized by well-demarcated areas of bright red skin that are typically rough, raised, and leathery. It occurs most often on the face but can also involve the hands, arms, legs, or feet. Warmth, pain, and swelling are common as well.

A range of symptoms typically precedes the appearance of the rash by anywhere from four to 48 hours. They may include:

• Fever
• Chills
• Headache
• Fatigue
• Anorexia
• Nausea
• Vomiting

The appearance of the rash is generally rapid and fast-spreading. The infection may extend beyond the superficial layers and cause the formation of tiny, fluid-filled blisters (vesicles) and pinpoint blood spots (petechiae). The lymph nodes nearest the infection may also become swollen, as can the skin overlying the lymph nodes.

Complications

Erysipelas can cause tiny cracks in the skin's barrier, allowing the bacteria to enter the bloodstream. In some cases, this can lead to a systemic bacterial infection known as bacteremia. If this happens, the infection can disseminate (spread) and begin to affect joints, bones, the heart, and the brain.

In rare cases, the dissemination of bacteria throughout the body can lead to endocarditis (a heart infection), septic arthritis, gangrene, or post-streptococcal glomerulonephritis (a kidney condition mainly affecting children).

If bacteremia persists, it can trigger a potentially deadly, whole-body inflammatory response known as sepsis (particularly in people with a weakened Immune system). Sepsis is characterized by fever, difficulty breathing, rapid heart rate, and mental confusion. In rare instances, it can lead to septic shock.

Causes

Erysipelas is caused by the bacterium Streptococcus pyogenes, which also can cause pharyngitis (sore throat) and strep throat. The face and hands are most commonly affected because a person with strep throat can cough and launch the virus onto the skin.

Erysipelas generally occurs when the bacterium enters a cut, abrasion, or other break in the skin and quickly multiplies and spreads via tiny lymph vessels just beneath the surface of the skin. In an attempt to neutralize the bacteria, the immune system will launch an inflammatory assault, causing local blood vessels to dilate and tissues to swell.

In some cases, the bacterium can penetrate uncompromised skin if there is pre-existing lymphedema (such as following a radical mastectomy where lymph nodes are removed). Without a lymphatic system to isolate disease-causing microorganisms, the skin is more vulnerable to local infections.

Risk Factors

Erysipelas most often affects elderly people and infants who have weaker immune systems and are less able to fight local infections. With that said, anyone can be affected, especially those with certain risk factors:

• Broken skin, including cuts, abrasions, insects bites, ulcers, animal bites, pinpricks, and burns
• Immune deficiency
• Eczema
• Psoriasis
• Athlete's foot
• Venous insufficiency
• Diabetes
• Being overweight
• Lymphedema
• Strep throat
• Prior history of erysipelas

Diagnosis

As it is so distinctive, erysipelas can usually be diagnosed by the appearance of the rash alone. Skin biopsies and cultures generally do not help with the diagnosis. Certain blood tests, such as a white blood cell (WBC) count or a C-reactive protein (CRP), may be useful in detecting immune activation and inflammation, but they cannot diagnose erysipelas.

To make a definitive diagnosis of erysipelas, a healthcare provider often needs to exclude other possible causes such as:

• Cellulitis
• Skin allergies, including insect bites
• Angioedema
• Contact dermatitis
• Herpes zoster (shingles)
• Drug allergy
• Stevens-Johnson syndrome
• Toxic epidermal necrosis

Erysipelas vs. Cellulitis

Cellulitis is similar to erysipelas in that it can be caused by Streptococcus pyogenes (as well as other streptococcal and staphylococcal bacterium). However, there are key differences between the two skin infections.

Cellulitis is typically slower to develop than erysipelas. With cellulitis, the affected skin is not nearly as red and rarely has well-defined borders. It is because erysipelas develops so quickly, overloading the skin will inflammation, that the fiery redness and demarcated rash occur.

Treatment

The standard treatment for erysipelas is antibiotics. Penicillin is generally the first-line treatment option for streptococcal infections. Other antibiotics may be used if there is an allergy to penicillin.

• Cephalosporin-class antibiotics
• Clindamycin (brand names Cleocin, Clindacin, Dalacin)
• Dicloxacillin (brand names Dycill, Dynapen)
• Erythromycin (brand names Erythrocin, E-Mycin, Ery-Tab)
• Azithromycin (brand names Zithromax, AzaSite, Z-Pak)

Most cases can be treated with oral rather than intravenous (IV) antibiotics. Any pain, swelling, or discomfort can be treated with rest, a cold compress, and elevation of the affected limb. Nonsteroidal anti-inflammatory drugs like Advil (ibuprofen) or Aleve (naproxen) can be used to relieve pain and fever.

If the face is involved, chewing should be minimized to avoid pain in which case, a soft diet may be recommended during the healing phase.

Treatment is often monitored by marking the borders of the rash with a marker pen. Doing so can make it easier to see if the rash is receding and the antibiotics are working.

In cases of sepsis (or when infections do not improve with oral antibiotics), IV antibiotics may be prescribed under hospitalization.

People with recurrent infections may need a prophylactic (preventive) dose of an antibiotic, taken daily, to prevent a recurrence.

A Word From Verywell

Erysipelas is a fairly common skin infection that is easily treated in most cases and rarely leads to complications. Still, if you have symptoms of erysipelas, you should call your healthcare provider right away. Quick treatment prevents the worsening of your condition and helps ease discomfort.