Medical Definition of Pinworm infection

Reviewed on 3/29/2021

Pinworm infection: An infection caused by a small, white intestinal worm: the pinworm or, more formally, Enterobius vermicularis. The pinworm is about the length of a staple and lives for the most part within the rectum of humans. While an infected person is asleep, female pinworms leave the intestines through the anus and deposit eggs on the skin around the anus. Because Enterobius vermicularis is a pinworm, pinworm infection is also called enterobiasis.

The symptoms of a pinworm infection are caused by the female pinworm laying her eggs. Most symptoms of pinworm infection are mild, and many infected people have no symptoms or, at most , some itching around the anus, disturbed sleep, and irritability. However, if the infection is heavy, these symptoms may be correspondingly more severe and also include loss of appetite, restlessness, and insomnia.

Pinworm is the most common worm infection in the United States. School-age children have the highest rates of pinworm infection. They are followed on frequency by preschoolers. Institutional settings, including day care facilities, often harbor cases of pinworm infection. Sometimes, nearly half of the children may be infected. Pinworm infection often occurs in more than one family member. Adults are less likely to have pinworm infection, except mothers of infected children.

Within a few hours of being deposited on the skin around the anus, pinworm eggs become infective (capable of infecting another person). They can survive up to 2 weeks on clothing, bedding, or other objects. Infection is acquired when these eggs are accidentally swallowed.

If pinworms are suspected, transparent adhesive tape or a pinworm paddle (supplied by your health care provider) are applied to the anal region. The eggs adhere to the sticky tape or paddle and are identified by examination under a microscope. The test should be done as soon as you wake up in the morning (because bathing or having a bowel movement may remove eggs). The exam may require several samples for diagnosis. Samples taken from under the fingernails may also contain eggs (since scratching of the anal area is common). At night, the adult worms can sometimes be seen directly in bedclothes or around the anal area.

Pinworm infection is treated with prescription or over-the-counter (OTC) drugs. Treatment involves a two-dose course. The second dose should be given 2 weeks after the first. Even with the availability of drugs OTC, you should consult your health care provider before treating a suspected case of pinworm.

If the pinworm infection occurs again, the infected person should be treated with the same two-dose treatment. Close family contacts should also be treated. If the infection occurs again, you should search for the source of the infection. Playmates, schoolmates, close contacts outside the house, and household members should be considered. Each infected person should receive the usual two-dose treatment. In some cases it may be necessary to treat with more than two doses. One option is four to six treatments spaced 2 weeks apart.

To prevent further pinworm infection, the following practices help reduce the risk of continuous self reinfection:

  • Bathe when you wake up (to help reduce the pinworm egg contamination).
  • Change and wash your underwear each day. Wear pinworm-free underclothing.
  • Frequent changing of night clothes is similarly recommended.
  • Change underwear, night clothes, and sheets after each treatment.
  • Open blinds or curtains in bedrooms during the day (because the pinworm eggs are sensitive to sunlight).
  • Personal hygiene should include washing hands after going to the toilet and before eating.
  • Trim fingernails short.
  • Don't bite nails (because of the danger of swallowing pinworm eggs).
  • Don't scratch bare anal areas (that is where the pinworm eggs are).

Measures such as cleaning and vacuuming the entire house or washing sheets every day are probably not necessary or effective. Screening for pinworm infection in schools or institutions is rarely recommended. Children may return to day care after the first treatment dose, after bathing, and after trimming and scrubbing nails.

This entry is based on information from the Division of Parasitic Diseases of the National Center for Infectious Diseases of the U.S. Centers for Disease Control and Prevention (the CDC).



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