September 2005

A 4-year-old boy presents to your office with the lesions shown in the accompanying photograph. Despite the mother applying various topical antibiotic ointments, the lesions come and go on the child’s arms and legs. No one else in the family (ie, the child’s parents, 7-year-old brother and 10-year-old sister) is affected. Some of the lesions are pruritic. Many of the blisters are filled with cloudy white fluid. What is your diagnosis?

Answer

At first glance, it is easy to jump to the conclusion that this child has bullous impetigo. Why, then, won’t the antibiotic ointment control the infection? Is this an infection with a resistant bacterial organism? How come the other family members are not affected?

Let’s go back to the history and physical examination, still important elements of the examination. You are told the lesions are pruritic. Impetigo can on occasion be symptomatic. Your examination reveals almost all lesions are acrally located. Aha, involvement of exposed surfaces!

Is this poison ivy? Probably not, due to the absence of linear or geometrically arranged lesions. How about insect bites? Further questioning reveals the family has no pets. No nearby relatives or close friends have pets. In fact, the mother said, “My child has never been in contact with any pets!” A bacterial culture of several of the bullous lesions yields normal skin flora.

This is a typical scenario when confronted with a child who has a bullous insect bite reaction. The parent frequently challenges your diagnosis and often asks for a referral to an “expert.” If you are lucky, a pediatric dermatologist practice is close by. By no means does this “expert” have an easier time convincing the parent that her child has insect bites.

Many times a disgruntled parent has left my office. Children who become highly sensitized to a biting insect can present with bullous lesions that look exactly like impetigo. The lesions are usually located in exposed areas of skin. The biting organism is usually a flea, especially during the winter months. Mosquito bites can also, on occasion, result in blistering lesions. Classically, insects tend to single out the youngest member of a family. This may be due to certain pheromones or other body odors that the insect is attracted to.

Pets are usually the normal host for fleas, especially baby kittens. Although most affected children come in contact with a pet in their own household, at times other scenarios exist. Contact can occur at a regular visit to a relative’s home where a pet lives, or at a playmate’s home. Some nursery schools and day cares may have resident pets that can lead to exposure to fleas. Babysitters may, unknowing to a family, bring a pet into the household. Here’s my favorite story. A family I was seeing for this very same problem had moved into a new home or apartment whose previous occupants had several pets. In cases like these, the hungry fleas will bite anyone they can!

Treatment of insect bites is very difficult. There are no effective medications that will quickly heal bite reactions. Most of the time, the physician must use medications that make the child comfortable while waiting for the lesions to heal. Obviously, prevention and elimination are most important. Professional elimination of the fleas from the household and the pet is vital and, unfortunately, not simple. Avoidance of contact with offending pets in environments other than the household is also critical. Keep as much of the skin surface covered with clothing as possible (day and night). Lastly, the safe use of an insect repellent will certainly reduce the frequency and number of bites. I like to apply the repellents to the child’s clothing rather than their skin. Most experts do not suggest using repellents with greater than 10% DEET. Unfortunately, that concentration of DEET does not always keep the insects away. If you are worried about the toxicity of DEET, other products are available (eg, oil of lemon eucalyptus or Picaridin).

No bites are good to have in great numbers, except for the “bytes” on your computer.

For more information:

• U.S. Environmental Protection Agency Web site: www.epa.gov/pesticides/factsheets/insectrp.htm#using
• Elston DM. Prevention of arthropod-related disease. J. Am Acad Dermatol. 2004;51(6):947.
• Harvey SC. Insect repellents and mosquito bites. N Engl J Med. 2002:347(21):1719.
• Sousa CA. Fleas, flea allergy, and flea control: a review. Dermatol Online J. 1997;3(2):7.