Cellulitis

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Cellulitis is a type of skin infection caused by bacteria. It involves the deeper layers of the skin and its underlying tissues, and is marked by a warm, red, spreading area on the skin. It is very common, often arising from a tiny break in the skin, and can sometimes be serious, especially in people with diabetes and certain other underlying medical problems. The bacteria that most often cause it are the gram positive bacteria group A streptococci and Staphylococcus aureus.

Cellulitis is treated with antibiotics.

The related skin infection erysipelas affects the more shallow layers of the skin.


Contents

Types

Cellulitis can affect the skin anywhere on the body, and in certain areas it has different names.

  • Perianal cellulitis affects the skin around the anus.
  • Orbital cellulitis, also called postseptal cellulitis, is a deep infection of the skin around the eye.
  • Periorbital cellulitis, also called preseptal cellulitis, is a more shallow or superficial infection of the eyelid and skin around the eye.
  • Submandibular cellulitis, also called Ludwig angina, is an infection of the tissues at the base of the lower jaw, underneath the mouth. It affects the skin to a lesser degree than it does the deep tissues, and is not, strictly speaking, cellulitis in the sense of the skin infection.

Signs and Symptoms

The hallmark of cellulitis is a painful, red, and tender area of skin, often with distinct borders that may slowly spread over time.

Other symptoms might include:

  • Skin that blisters and then scabs over
  • Fever and chills
  • Swollen glands, or lymph nodes
  • Red streaking heading toward the center of the body, which means the infection has spread to the lymphatic system

In people with chronically swollen arms or legs (lymphedema), cellulitis may occur over and over in the swollen areas.

Causes

Although a variety of bacteria can cause cellulitis, Streptococcus bacteria are the most common cause. Streptococcus bacteria, or Strep as they are often called, can be divided into several groups based on a certain component in the bacteria's outer wall. Group A and group B strep cause most human disease, and group A is the type that causes cellulitis.

The most important species of group A Streptococcus is Streptococcus pyogenes. Besides causing cellulitis, it can also cause the other very serious group A strep infections necrotizing fasciitis and streptococcal toxic shock syndrome. Group A strep are also responsible for "Strep throat".

Another very common cause of cellulitis is Staphylococcus aureus. Bacteria in the genus Staphylococcus can also cause the skin infections erysipelas and necrotizing fasciitis.

Methicillin-resistant Staphylococcus aureus (MRSA) can be a particular cause for concern due to its resistance to a number of antibiotics. When MRSA began to emerge, it occurred only in hospitalized patients, causing nosocomial infections (hospital-acquired infections). But it has become increasing common as a community-acquired infection, and, in fact, a landmark 2004 study found it had become the most common cause of skin abscesses in 11 urban areas of the US.[1] It can also cause cellulitis.[2]

Diagnosis

Diagnosis of cellulitis is made by looking at the abnormal skin. Occasionally, a doctor takes a sample to see if the bacteria can be cultured (grown), but this only rarely works and is not necessary for diagnosis. In the uncommon event that the bacteria need to be identified, injecting sterile saline solution into the cellulitic area of skin, then withdrawing some of that fluid, may help to capture some bacteria for culture.[3]

If a blood infection is suspected, blood samples are drawn and sent for culture to see if the bacteria are in the blood.
Group A S. pyogenes showing its ability to break open red blood cells, a property called beta hemolysis. The broken cells show up as a white halo around the circular colonies in the center. Source: CDC

Exams and Tests

The bacterial culture, if it is done, sometimes reveals what kind of bacteria are causing the infection. Tests may also be performed to check for antibiotic resistance—that is, to see whether the bacteria can be stopped with the antibiotic being used.

  • skin biospy
  • ESR
  • temperature
  • lymph node biopsy
  • RBS
  • dopamine level
  • blood culture

Treatment

Depending on how severe the infection is, a healthcare provider will prescribe either oral or intravenous (through the vein) antibiotics. For most people, a drug that stops both Group A Streptococcus and S. aureus is given, typically a penicillin or cephalosporin. (Both these types of antibiotics fall into the beta lactam family of drugs.) Drugs commonly chosen to treat cellulitis include dicloxacillin and cephalexin, which can be taken in pill form. Although MRSA has become a very common cause of skin abscesses, and cannot be treated with the above beta-lactam medications, beta-lactams may still be reasonably effective for cellulitis without abscess, according to one 2008 study.[2] If a beta-lactam doesn't cure the cellulitis, drugs active against MRSA should be tried next.

Drugs given for cellulitis through an intravenous line include ceftriaxone, nafcillin, and in severe cases linezolid, ertapenem, or the combination imipenem and cilastatin may be used. Because MRSA is becoming so common and is resistant to some standard antibiotics, the very powerful antibiotic vancomycin may also be used those in patients whose infection is severe enough to need hospitalization, and in patients with lowered resistance due to diabetes or other diseases. Keeping the infected areas elevated (such as putting the feet up) and using topical (on the skin) antibiotic ointments may also be needed.

Because cellulitis spreads rapidly—it may advance past a boundary marked in ink over just a few hours—it is important to start antibiotics as soon as possible. Patients should return in about 24 hours for a checkup to make sure the treatment is working.

Topical antibiotic cream may help locally.

Prevention

Especially in people with weakened Immune System|immune systems or who have diabetes, it is important to keep minor abrasions, cuts, bruises, and burns clean and to avoid repeated skin trauma. This includes excellent foot care, as cracks between the toes can cause such infections in diabetics. People with peripheral edema, or swelling in the legs, from heart failure , liver conditions and other conditions may benefit from wearing skin compression stockings to help prevent skin breakdown and the cellulitis that may result.

Chances of Developing Cellulitis

Cellulitis usually begins with a minor incident, such as a bruise. It can also begin at the site of a burn, surgical cut, or wound, or any other break in the skin. Cellulitis can also complicate other diseases that affect the skin, such as measles, ringworm, shingles or chicken pox. These diseases cause the skin's normal defenses to be lost in certain spots, and bacteria can enter and begin an infection.

Many people are carriers of the bacteria that cause cellulitis. The germs live in their skin or inside their noses, and may be passed on to others.

Risk factors

Besides broken or damaged skin, the following circumstances can raise a person's risk of getting cellulitis.

  • Diabetes: Diabetes is a risk factor for many serious infections, as the immune system is somewhat suppressed in people with the disease.
  • Immunosuppression: People with a faulty or damaged immune system, such as people with HIV or those receiving chemotherapy or taking long courses of steroids, are at higher risk for infections like cellulitis.
  • Impaired circulation: People who have peripheral vascular disease, in which the arteries to the arms and legs are not bringing enough blood, and people with chronically swollen body parts, are at higher risk for cellulitis. A brisk blood circulation is an important part of keeping infections at bay, and sluggish circulation removes this defense.
  • Contact sports: Recent outbreaks among high school and college football players have increased concern about cellulitis and erysipelas among contact sport participants. These people are at increased risk because of the frequency of skin trauma and the crowded conditions in many locker rooms.[4]

Related Problems

Complications

  • Abscess, the development of a pocket of pus that must be drained.
  • Bacteremia, a condition in which the bacteria causing the skin infection get into the bloodstream.
  • Lymphangitis, or involvement of the lymph nodes—a complication that shows up as red streaks leading away from the cellulitis.
  • Thrombophlebitis, or inflammation of a vein that occurs when a blood clot forms.
  • Necrotizing fasciitis, a very dangerous infection of the connective tissue beneath the skin.
  • Gas gangrene, in which bubbles appear in the skin and death of tissue occurs. This is more common in diabetics and may require amputation.

Clinical Trials

For a list of American government-sponsored clinical trials involving cellulitis, click here.

Expected Outcome

As antibiotics are typically able to resolve the infection, the prognosis for people who have cellulitis without complications or underlying medical conditions is good.

Links to Clinical Images

Hardin MD: Cellulitis Images


DermAtlas: Cellulitis Images

Skinsight: Cellulitis Images

DermNetNZ: Cellulitis Images

References

  1. Moran GJ, Krishnadasan A, Gorwitz RJ, et al. Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med. 2006; 355(7):666-674. Abstract | Full Text
  2. 2.0 2.1 Madaras-Kelly KJ, Remington RE, Oliphant CM, Sloan KL, Bearden DT. Efficacy of oral beta-lactam versus non-beta-lactam treatment of uncomplicated cellulitis. Am J Med. 2008 May;121(5):419-25. Abstract
  3. Oill PA, Montgomerie JZ, Cryan WS, Edwards JE. Specialty conference. Infectious disease emergencies. Part V: patients presenting with localized infections. West J Med. 1977 Mar;126(3):196-208. Abstract | Full Text
  4. R Romano, D Lu, and P Holtom. Outbreak of Community-Acquired Methicillin-Resistant Staphylococcus aureus Skin Infections Among a Collegiate Football Team. J Athl Train. 2006; 41(2): 141–145.
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