Impetigo Skin Infection – Causes, Symptoms, Treatment

What is impetigo?

Impetigo refers to a bacterial skin infection that affects the outermost layers of the skin. The skin is a tough physical barrier against environmental pathogens. However, the skin can also get infected when the outermost layers of the skin are breached through cuts. Even minor cuts can cause bacterial infections. Impetigo is a common bacterial skin infection in infants and children.

It is estimated to account for about 10% of the skin infections seen in the pediatric patients. It is important to stress that impetigo is a highly contagious skin infection that can spread easily through close contact. Impetigo can also progress to some serious complications such as kidney disorders and cellulitis, when a severe infection is left untreated.

The most common cause of impetigo are bacteria of the Staphylococcus and Streptococcus genus. These bacteria can be found on the skin, and can gain entry into the body through cuts and injuries on the surface of the skin. Usually, impetigo resolves on its own in a matter of weeks. In some cases, treatment with antibiotics may be required.

Types of Impetigo

Impetigo can be classified into the following two types:

  1. Nonbullous impetigo: Nonbullous impetigo is the most common type of impetigo. It occurs when there is a break in the skin and the body responds to the infection. The blisters formed in nonbullous impetigo are smaller compared to the blisters in bullous impetigo.
  2. Bullous impetigo: Bullous impetigo is caused by toxins released from the invading bacteria. This condition is characterized by the formation of large blisters. Bullous impetigo may occur even when the body does not respond to the infection.

Signs and Symptoms

A characteristic feature of impetigo is the formation of small, red blisters on the skin area where the infection occurs. The infected skin area also turns red. The most common sites of infection are the arms, legs, and face. However, impetigo infections can occur anywhere on the body. The blisters can become filled with pus, and eventually rupture. The infected area can be itchy, tender and painful.

A few days after the onset of infection, a thick yellow or brown crust may form over the infected area. In some cases, the infection may spread to deeper underlying tissues, resulting in the formation of ulcers. The lymph nodes in the region of infection may also get enlarged. However, unlike in other infections, fever may not be present.

Causes of Impetigo

The most common cause of impetigo are bacteria belonging to the Staphylococcus and Streptococcus genus. A number of different bacteria belonging to these two genus can cause impetigo.

Among them, Staphylococcus aureus (commonly abbreviated as S. aureus) and group A beta-hemolytic streptococci (abbreviated as GABHS) are responsible for the majority of cases of impetigo. Staphylococcus aureus is responsible for almost all cases of bullous impetigo. About 20% of the cases of bullous impetigo are caused by methicillin-resistant S. aureus (abbreviated as MRSA).

Read more on Staphylococcus aureus.

GABHS and Streptococcus pyogenes are responsible for most cases of nonbullous impetigo. Bullous impetigo can occur even on intact skin. These infections are restricted to the superficial layers of the skin. Disruption of skin that may result in impetigo can happen due to dermatitis, scratching, chickenpox, burns, scabies, insect bites and radiation exposure. It is important to note that the disruption of the skin barrier may not always be visible.

Risk Factors

A weakened immune system, caused by conditions such as corticosteroid use, diabetes, HIV infection, and other systemic diseases increases the risk of impetigo. Intravenous drug usage also increases the risk of impetigo infection. Due to the highly contagious nature of the disease, close physical contact with infected persons is a high risk factor.

Complications of Impetigo

In most cases, impetigo resolves on its own. However, in some cases, impetigo may lead to serious complications. Impetigo may cause infection of the deeper tissue layers under the skin (ecthyma), leading to formation of ulcers and scars. When the infection reaches the subcutaneous tissues (a condition known as cellulitis), it could cause a life-threatening situation. Prompt treatment is required in such cases.

Another common complication of impetigo is a kidney disease known as acute poststreptococcal glomerulonephritis. This condition is seen in about 20% of the impetigo patients. In rare cases, the infection may also spread to the blood (causing sepsis) and the bone (causing osteomyelitis). These complications are more likely to occur in adults with a weakened immune system.

Treatment of Impetigo

In most cases, impetigo resolves on its own without any treatment. It may take up to 2-3 weeks for the infection to clear on its own. If the infection is severe or complications begin to arise, then antibiotics are prescribed. For localized infections, antibiotics may be given in the form of topical ointments.

If a crust has formed over the infected skin area, then the area should be cleaned with soap and water before applying any antibiotic ointment. Oral antibiotics are prescribed in cases of widespread impetigo infection and presence of complications.  Treatment with antibiotics can remove the infection in a week’s time. However, the prescribed antibiotic course must be completed in order to prevent a recurrence of the infection.

Preventing Impetigo

Since impetigo is a contagious condition, preventive measures need to be taken to halt the spread of the infection. Healthy children should not be allowed to have close physical contact with infected children till the infection resolves. General hygienic measures such as washing hands with soap and keeping short fingernails can help in preventing the spread of impetigo. When there are breaks in the skin, the affected area needs to be kept clean. Scratching should be avoided, especially in areas where skin breaks are present. Antiseptic lotions can be applied to sites of injury till the skin barrier reforms.

How Impetigo differs from Cellulitis

Cellulitis refers to inflammation caused by an infection of the subcutaneous tissue layers. It is a serious complication of impetigo. Cellulitis can extend from the upper parts of the subcutaneous tissues to the deeper dermis. The arms and the legs are the most frequent sites of cellulitis.

The bacteria that cause cellulitis can be found on the surface of the skin, and in the oral and nasal cavities. These bacteria do not normally cause any infection. Bacteria may also be picked up from the environment, such as water or inanimate objects.

The main feature of cellulitis is inflammation. All the signs and symptoms of inflammation (such as redness, swelling, pain, and heat) are present in the affected region. Blisters may also form on the surface of the skin. Pus may accumulate at the infected site. Fever, chills and enlargement of lymph nodes in the affected region may also be evident.

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