What Causes Impetigo?

Impetigo is a highly contagious skin infection commonly found in children, learn what causes this disease.

What is impetigo?

Impetigo is a fairly common, highly contagious skin infection, usually caused by Group A streptococci bacteria, by Staphylococcus aureus, or by a combination of the two. Occasionally impetigo is caused by other types of bacteria, but these two are by far the most common agents of infection.

How does impetigo occur?

Normally the skin provides a very effective barrier and protects the body from infection. But when the skin is broken, as by a cut or scratch, an insect bite, a burn, or a pre-existing skin rash caused by eczema or by an allergic reaction to poison ivy, soap, or cosmetic products, bacteria can enter and cause infection.

What are the symptoms of impetigo?

Usually a cluster of small blisters or red bumps appears first at the site of infection. These blisters will grow and rupture within about twenty-four hours. The skin exposed when the blisters burst appears red and inflamed, and will often leak either pus or a thinner fluid, which may be clear or slightly cloudy. If the infection is left untreated, the lesions may grow quite large, and will almost certainly spread to other parts of the body.

Over a period of four to six days, the lesions will begin to form thick tan or honey-colored crusts.

What parts of the body are most likely to be infected by impetigo?

The skin on any part of the body can be infected by impetigo, but the infection usually occurs initially on skin that is not covered by clothing, especially on the face (usually around the nose and mouth) and on the hands. The arms and legs, too, are common sites for impetigo infection, though less so than the face and hands.

Who is likely to be at risk for contracting impetigo?

Anyone can get impetigo, but it is most commonly found in children, probably because they so often have cuts, scrapes, insect bites, or other minor injuries on their skin from playing outdoors.

People living or working in crowded conditions, such as schools, daycare facilities, and military bases, are also at higher risk of being infected through contact with another person who already has the infection or, less commonly, through contact with clothing, towels, or bedding contaminated by discharge from impetigo lesions.

Family members of a person who already has impetigo are similarly at risk of contagion from direct contact with discharge from the lesions. Impetigo is highly contagious. Whenever one person has impetigo, precautions must be taken to prevent it from spreading to others.

Are there other risk factors for developing impetigo?

Because bacteria thrive in warm, moist environments, most cases occur during the hot, humid summer months. That is also the time when children are outdoors playing in shorts and short-sleeved shirts, so they are more likely to have small skin injuries that provide an opening for the bacteria.

Poor nutrition, poor personal hygiene, unsanitary living conditions, or an illness that has lowered an individual's resistance are also risk factors for developing impetigo.

How does one contract impetigo in the first place?

Bacteria live on the surface of the skin. If a skin injury is not kept clean, it is an invitation for those bacteria to invade the body and cause infection. Good personal hygiene helps to keep the bacteria in check, both as a preventive measure, and as part of the treatment schedule if one does develop impetigo. (A person who has suffered from several bouts of impetigo, especially if his immune system has been compromised, might want to regularly use an antiseptic soap to guard against recurrence.)



Although many cases of impetigo do arise spontaneously because the bacterial agents exist already on the skin and in the environment, most cases are probably contracted by coming into direct contact with discharge from an impetigo lesion. This can occur either by touching the lesion or, less commonly, by coming into contact with such articles as clothing, towels, or bedding that have been contaminated by discharge.

How can the spread of impetigo be prevented?

To prevent the patient from spreading impetigo to other parts of his body, he should avoid scratching or touching the lesion. A child may find it hard to follow this directive, especially as impetigo itches. A child who has impetigo should have his fingernails cut short. It will also probably be necessary to cover the infected areas with gauze and surgical tape. Plastic bandages should be avoided, however, because they create a warm, moist environment that would encourage the growth of bacteria and slow the healing process.

To prevent impetigo from spreading to other members of the household, each person in the family should have his own towels, and the towels, clothing, and bedding of the patient should be laundered daily until after the patient has been taking antibiotics for forty-eight hours, at which point he should no longer be contagious. The person who washes and bandages the impetigo lesions should carefully wash his or her hands after direct contact with the sores, and used bandages should also be disposed of carefully.

Because children are so susceptible to impetigo, it is important that they practice good personal hygiene, and that minor skin injuries be monitored for the small blisters that are characteristic of the early stage of the infection. It is easier to prevent impetigo or to treat it and prevent contagion when it is in its early stages than when lesions have begun to spread and to discharge fluid.

If impetigo does develop, how should it be treated?

Impetigo is usually treated with oral antibiotics. Parents, daycare workers, and teachers should familiarize themselves with the signs of impetigo. If a child has such signs, especially if he has been exposed to someone who has the infection, he should be seen by a doctor.

The doctor will diagnose impetigo on the basis of the appearance of the blisters or lesions, but a culture is also needed to determine precisely which bacterium, or combination of bacteria, is responsible for the infection. The choice of antibiotic is determined by the type of bacteria involved. If the wrong antibiotic is prescribed, it may not cure the infection or prevent it from spreading to others, and a new course of antibiotics will have to be tried. But taking a culture can ensure that the most effective antibiotic is chosen. If an oral antibiotic is prescribed, it must be taken as directed until all the medicine is gone.

In the earliest stages, impetigo can sometimes be cured by applying an antibiotic cream or ointment, such as polysporin, four times daily until the infection disappears. But once the lesions begin to grow or spread, it is almost always necessary to turn to oral antibiotics. In fact, in stubborn cases the doctor might recommend both oral antibiotics and antibiotic ointment. After applying an antibiotic ointment, the affected area should be loosely covered by a gauze bandage.

Antibiotics should produce clear signs of healing within three days, and after four or five days healing will usually be complete. If the sores are not completely healed within a week after treatment begins, the patient should return to the doctor for another examination.

While the skin lesions are healing, they should be cleansed daily, using an antiseptic soap. If an area is crusted, soak it in warm, soapy water before washing, in order to remove the crust. If an antibiotic ointment is to be applied, the crusts should be removed first.

When can a child return to school or daycare?

A child with impetigo should be kept home until he has been on antibiotics for forty-eight hours. At that point, he will no longer be contagious. If he is being treated only with antibiotic ointment for a very mild infection, he can return to school or daycare as soon as his skin has completely healed.

Why can't we just let the body's immune system fight off the infection?

Everyone who works with children should find and examine a picture of a case of impetigo that has been left untreated. The number, size, and hideousness of the lesions would persuade anyone that this condition, though fairly common, must be taken seriously. Such pictures are readily available in medical textbooks and on medical websites.

Furthermore, if left untreated, a single case of impetigo can lead to several more, either within a single household or throughout a school, a daycare facility, or any other setting where people, especially children, are likely to come into close contact with each other.

Even apart from the terrible sores and the danger of contagion, an untreated case of impetigo can have potentially deadly consequences. If the responsible bacterium is streptococcus, it may invade beyond the skin and develop into scarlet fever. This disease, which is caused only by certain strains of the strep bacterium, is characterized by high fever, chills, vomiting, sore throat, and a fine red "sandpaper" rash. It can be successfully treated with antibiotics, but if left untreated can damage major organs and even lead to death. In rare cases, the bacterium can also cause post-streptococcal glomerulonephritis, an infection of the kidneys that follows about ten days after a strep infection and causes temporary kidney failure. This condition, too, responds well to antibiotics""if it is treated in a timely fashion.

But obviously it is better to keep an eye on the minor skin injuries a child inevitably has, and to identify and treat impetigo in the early stages, before it spreads and well before it has a chance to develop into something far more serious.

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