Impetigo – Pathophysiology, Complications, and Diagnosis.

What is impetigo?

Impetigo is an infection of the outer layer of the skin. Its most often caused by the bacteria Staphylococcus aureus or Streptococcus pyogenes. Impetigo is much more common in children, but adults can get it too. It’s more common in the summer months.

Normally, your skin is covered by millions of bacteria. Many of these are harmless, and some may be good for you. But sometimes harmful bacteria can grow on your skin. If these get through the outer layer of your skin (epidermis), they may start to grow more. This can cause impetigo.

Types of Impetigo

There are 3 kinds of impetigo:

  • Nonbullous impetigo. This is the most common form in adults. They cause thick, honey-colored crusts.
  • Bullous impetigo. This causes large blisters on the skin.
  • This type is a more serious form that usually results from untreated impetigo and causes ulcerative sores that go down into the deeper layers of the skin.

Some impetigo is caused by a type of bacteria called methicillin-resistant Staphylococcus aureus (MRSA). This type of bacteria is hard to kill. This type of impetigo can be difficult to treat.


Intact skin is usually resistant to colonization or infection by S. aureus or Group A beta-hemolytic Streptococcus (GABHS). These bacteria can be introduced from the environment and only transiently colonize the cutaneous surface. Experimental studies have shown that inoculation of multiple strains of GABHS on to the surface of subjects did not produce cutaneous disease unless skin disruption had occurred.

The teichoic acid adhesions for GABHS and S. aureus require the epithelial cell receptor component, fibronectin, for colonization. These fibronectin receptors are unavailable on intact skin; however, skin disruption may reveal fibronectin receptors and allow for colonization or invasion in these disrupted surfaces. Factors that can modify the usual skin flora and facilitate transient colonization by GABHS and S. aureus include high temperature or humidity, preexisting cutaneous disease, young age, or recent antibiotic treatment.

Common mechanisms for disruption of skin that can facilitate bacterial colonization or infection include the following:

  • Scratching
  • Dermatophytosis
  • Varicella
  • Herpes simplex
  • Scabies
  • Pediculosis
  • Thermal burns
  • Surgery
  • Trauma
  • Radiation therapy
  • Insect bites

Immunosuppression by medications (eg, systemic corticosteroids, oral retinoids, and chemotherapy), systemic diseases (eg, HIV infection, diabetes mellitus), intravenous drug abuse, and dialysis encourages bacterial growth.

After initial infection, new lesions may be seen in areas with no apparent break in the skin. Frequently, however, upon close examination, these lesions will demonstrate some underlying physical damage.

What causes impetigo?

  • The main cause of impetigo is a bacterial infection. The bacteria usually enters the skin through a cut, scrape, rash or insect bite.
  • Most of the time, the cause is the Staphylococcus aureus (“staph” bacteria). Sometimes, group A Streptococcus bacteria can cause it. This type of bacteria also leads to strep throat and fever.
  • Certain strains of strep bacteria that cause impetigo can also cause glomerulonephritis. This inflammatory kidney disease can produce high blood pressure and blood in the urine.

Risk factors of Impetigo

Anyone can get impetigo, but some factors increase someone’s risk of getting this infection.

  • Age: Impetigo is most common in children 2 through 5 years old.
  • Climate: Impetigo is more common in areas with hot, humid summers and mild winters (subtropics), or wet and dry seasons (tropics).
  • Infections or injuries that break the skin: People with scabies infection are at increased risk for impetigo. Participating in activities where cuts or scrapes are common (sports) can also increase someone’s risk of impetigo.
  • Close contact or crowding: Close contact with another person with impetigo is the most common risk factor for illness. For example, if someone has impetigo, it often spreads to other people in their household. Infectious illnesses also tend to spread wherever large groups of people gather together. Crowded conditions — such as those in schools and daycare centers — can increase the spread of impetigo.

Symptoms and types

Symptoms of impetigo usually appear 2–10 days after infection.

The main symptoms are blisters or sores that burst and ooze before drying up. Other symptoms will depend on the type of impetigo.

There are three types:

  • Non-bullous
  • Bullous
  • Echythema

Non-bullous impetigo

  • Around 80% of cases are of this type. It usually starts as a small blister but can spread quickly. The blisters often join together as it spreads.
  • The blisters tend to affect the face and the extremities.
  • As the blisters burst and weep, a honey-colored crust forms. There may also be redness and swelling in the area.
  • In rare cases, a person may have a fever and other systemic symptoms.
  • Nine out of 10 cases are among children under age 2.

Bullous impetigo

  • This involves fewer blisters, but they are larger. They often affect the trunk of the body and may appear in the mouth.
  • The blisters contain a clear or yellow fluid, which becomes cloudy or dark over time. The blisters stay longer without bursting than in non-bullous impetigo. There is not usually redness or swelling, and there is no honey-colored crust.
  • However, as a blister bursts, it will leave a red mark with a scaly rim around it.
  • A fever and other general symptoms may occur.


  • In this type of impetigo, ulcers develop on the skin and enter the deeper layers.
  • The ulcers are indented into the skin with red or purple edges and a brown or honey-colored crust. They may produce pus.

Complications from impetigo

Soft tissue infection

The bacteria causing impetigo can become invasive, leading to cellulitis and lymphangitis; subsequent bacteraemia might result in osteomyelitis, septic arthritis or pneumonia.

Staphylococcal scalded skin syndrome

In infants under six years of age or adults with renal insufficiency, localised bullous impetigo due to specific staphylococcal serotypes can lead to a sick child with generalised staphylococcal scalded skin syndrome (SSSS). Superficial crusting then tender cutaneous denudation on the face, in flexures, and elsewhere is due to circulating exfoliatin/epidermolysin, rather than a direct skin infection. It does not scar.

Toxic shock syndrome

Toxic shock syndrome is rare and rarely preceded by impetigo. It causes fever, diffuse erythematous then desquamating rash, hypotension and involvement of other organs.

Post-streptococcal glomerulonephritis

Group A streptococcal infection may rarely lead to acute post-streptococcal glomerulonephritis 3–6 weeks after the skin infection. It is associated with anti-DNase B and antistreptolysin O (ASO) antibodies.

Rheumatic fever

Group A streptococcal skin infections have rarely been linked to cases of rheumatic fever and rheumatic heart disease. It is thought that this occurs because strains of group A streptococci usually found on the skin have moved to the throat (the more usual site for rheumatic fever-associated infection).

What tests and procedures diagnose impetigo?

Diagnosing an impetigo infection is generally straightforward and based on the clinical appearance. Occasionally, other conditions may look something like impetigo. Skin infections such as tinea (“ringworm”) or scabies (mites) may be confused with impetigo. It is important to note that not every sore or blister means an impetigo infection. At times, other infected and noninfected skin diseases produce blister-like skin inflammation. Such conditions include herpes cold sores, chickenpox, poison ivy, skin allergies, eczema, and insect bites.

Secondary skin infections may sometimes occur. Medical evaluation and occasionally culture tests are used to decide whether topical antibacterial creams will suffice or whether oral antibiotics will be necessary.

What are the Treatments for Impetigo?

The key to treating — and preventing — impetigo is to practice good personal hygiene and maintain a clean environment. Once you get the infection, it’ll take prompt attention to keep it under control and prevent it from spreading.

Keep clean: Even if only one family member has impetigo, everyone in the household should follow the same cleaning routine. Wash regularly with soap and water. This should help clear up mild forms of the infection. If this doesn’t help, seek care from your doctor. You may need a prescription medication.

Topical antibiotics: Mupirocin ointment, available only by prescription, works well to treat mild forms of the infection. Soak the sores in warm water first and gently remove any scabs so the antibiotic can reach your skin. Don’t try over-the-counter antibacterial ointments; they are too weak to kill strep and staph infections. Applying the ointment carelessly may actually spread the impetigo. For repeated outbreaks, your doctor will prescribe an antibacterial ointment that goes inside the nose for everybody in the household. It will kill nasal bacteria.

Oral antibiotics: If you have a more serious or widespread infection, you may need to take a medicine like amoxicillin for a week or so.

Bleach baths: You can lower the amount of bacteria on your skin by soaking in a mild bleach solution for about 10 minutes at a time a couple of times a week. Use ½ cup of normal household bleach for a full tub, ¼ cup for half a tub. Rinse off with clean water and pat dry.  If you’re sensitive to chlorine, you may not want to try bleach baths. They can cause a skin reaction or asthma flare.

Anyone in your house who gets impetigo should use a clean towel every time they wash. Launder those towels separately, using hot water and a hot dryer to kill the bacteria. Keep sores covered to prevent spreading the infection to other body parts or other people.

Prevention of Impetigo

Children with impetigo should stay home until they are no longer contagious if the lesions can’t be reliably covered. Adults who work in jobs that involve close contact should ask their doctor when it’s safe for them to return to work.

Good hygiene is the no. 1 way to prevent impetigo. Follow these tips:

  • Bathe and wash your hands often to cut down on skin bacteria.

  • Cover any skin wounds or insect bites to protect the area.
  • Keep your nails clipped and clean.
  • Don’t touch or scratch open sores. This will spread the infection.
  • Wash everything that comes into contact with the impetigo sores in hot water and laundry bleach.
  • Change bed linens, towels, and clothing that come in contact with the sores often, until the sores are no longer contagious.
  • Clean and disinfect surfaces, equipment, and toys that may have come in contact with impetigo.
  • Don’t share any personal items with someone who has impetigo.







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