Expert Advice -- Pinworms: Why do they keep coming back?

My son has just gotten pinworms for the third time. Is there something that I am doing wrong? Why does he keep picking them back up?


Robert Steele

Robert W. Steele, MD, is a board certified pediatrician at St. John's Regional Health Center in Springfield, MO. He graduated from medical... Read more

Pinworms are extremely common. It is estimated that up to 42 million people in the U.S. have this parasite in their intestines. They have been discussed in circles that go as far back as the physicians in ancient Rome and Greece. But it wasn't until the 1930's and 40's when the National Institutes of Health extensive studied this organism. Much of what we know today comes from that research.

The pinworm circle of life goes something like this:
People become infected by swallowing or inhaling the eggs. The eggs reach the intestines where they hatch. It takes between two weeks and two months before the female becomes about 1/2 inch in size and mature enough to lay eggs. To lay her eggs, the pinworm migrates from the where the large intestine begins down to the anus. It deposits the eggs by making jerking motions. The current thought is that these motions are what cause the itching. The child scratches his bottom, and the eggs which are quite sticky are picked up and transmitted back to himself or someone else.

Now, before I gross out all the readers (perhaps it is too late), realize that we have a lot of bacteria and other bugs on and inside our bodies that do not seem to cause any problems. In fact, some bacteria are quite beneficial. Pinworms are not bacteria; they are a type of roundworm, but they do not usually cause any problems by living in our intestines. On rare occasions, they may end up in places other than the intestine and then cause some problems. However, most of the time they live in the colon, only cause some itching in the child who has them but cause a lot of anxiety in the child's parents.

The most common symptoms of pinworms are itching (particularly at night), restless sleep, awakening at night in a child who usually sleeps through the night, and scratching the anal area. Much less commonly they may cause itching in the vaginal area due to them migrating to this area, or hives in those who are allergic to them. Notably, they do NOT cause grinding of the teeth, nail biting, or nose picking.

The diagnosis is made in an interesting way. Tape may be placed against the anus either by the doctor or by the parent during times of itching. The eggs and occasionally a worm will get stuck to the tape. Then, the tape is examined under the microscope. Alternatively, the doctor may do a rectal examination and look at the stool under the microscope. Collecting stool at home for examination does not seem to be a good way to find these little critters because they tend to stick to the anal area a lot better than falling off in the stool.

Treatment may be done using any number of medications. The most common one for children is called mebendazole (Vermox). However, gaining control over this infection may be difficult due to a number of reasons, so here are some suggestions:

• Because pinworms are so common and easily transmitted, it is more the rule than the exception that multiple family members are infected even though they may not be experiencing symptoms. Therefore, treatment of the entire family with medication is often required.

• The eggs are spread from hand to mouth. The eggs have to get to the hands to do this, so limiting access to the anal area can be helpful. This might be done by dressing small children in closed garments such as all-in-one pajamas. Keeping the fingernails short and frequent hand washing will help as well.

• The eggs will stick to other things in the environment. Simple washing and vacuuming is all that is required. There is no need to go crazy and do an extensive house cleaning, however, concentration on those things the child is regularly touching is more helpful. These items include the bedding, stuffed animals or blankets that occupy the bed, bathroom cups, toothbrush, toothpaste tubes, and doorknobs are some examples.

I realize these pinworm reinfections must be frustrating for you. Try to remember, the fact that your son has these infections is in no way a reflection on you as a parent. Your story is not an uncommon one because of how ubiquitous these creatures are. I suggest you review the suggestions above to see if you can implement them during this round of infection, and with some luck, you will finally get rid of them.

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