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The Informed Parent

What Is Impetigo?

by Louis P. Theriot, M.D., F.A.A.P.
Published on May. 30, 2011

Mrs. J. anxiously came to the office after picking up her 4-year-old son from pre-K. The school had called and said that he had “impetigo.” He was contagious and had to be taken home. Without making an appointment she just stopped by on her way home. She was embarrassed, flustered and worried.

“What the heck is impetigo?” she asked nervously. She went on to say in a defensive tone, “Good hygiene is the standard in my house, and I resent anyone suggesting that my son is not clean. I resent the notion!”

After examining the boy, sure enough, he had impetigo around the nose and a couple of small lesions nearby on the upper lip. No fever or swollen lymph nodes and otherwise he was just fine. To put her mind at ease, I said that before we talk about treating this, it is important that she understand what impetigo really is.

Two physicians, Dunn and Fox, first described impetigo in the medical literature in 1860. It is a very common and highly contagious skin infection that affects infants and children. The peak age of impetigo is between 2 and 6 years. It is more common during the warmer months, usually in summer and fall.

Impetigo is caused by two different types of bacteria--staphylococcus aureus and streptococcus pyogenes. These bacteria typically live on our skin and are harmless. If there is a disruption in the integrity of the skin, they can then become infected and cause impetigo. This may occur if there is a scratch, an abrasion, or an insect bite. About 30% of people are colonized with staph in their nose, which means that the bacteria are present there. But nothing is causing any symptoms or problems until there is a break in the skin.

There are two main types of impetigo. The first is non-bullous or impetigo contagiosa. This starts as a small, red, bite-like lesion that rapidly spreads and oozes a clear or pus-like fluid that forms a yellowish crust. The classic description of an impetigo lesion is a “honey-colored crust on a red base.” These may start around and inside the nose, around the mouth, near the earlobe or near the chin. There may just be a single lesion initially. Within a few days it may spread so that there are a few new lesions nearby. These lesions may be itchy but are not painful. There is usually no fever or any other symptoms. However, if untreated they are certainly likely to spread.

The second type is bullous impetigo. These lesions erupt quickly as a papule that forms a thinly covered, fluid filled blister that bursts and leaves a red base with a yellow, crusty scab. The bullae, or blisters, are caused by a toxin that is produced by certain staphylococcal bacteria. This toxin reduces the cell-to-cell adhesion in the skin. This causes a separation between the outer layer of skin, the epidermis, and the underlying dermis. This allows the fluid to accumulate in this space forming the blister.

Non-bullous impetigo may be caused by staph or strep, and they present very similarly. This type of impetigo is by far the more common type, and accounts for around 70% of impetigo in patients under the age of 15 years. The sites of predilection are the nose, mouth, chin or ear.

Bullous impetigo is much less common and tends to occur more frequently in young infants. These lesions tend to appear in the neck, armpit region and diaper area.

Some articles refer to a more invasive type of impetigo called ecthyma. This is a deeper, more penetrating infection that reaches down into the dermis. It forms a shallow ulcer that has an angry red base with yellowish fluid that will crust into a grayish-yellow scab. These lesions tend to be painful and may cause enlarged local lymph nodes. Unlike the typical types of impetigo, non-bullous and bullous, this type may cause scarring as it is a deeper infection.

Next month we will discuss how to treat these infections.

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