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Pinworm Infestation

(Enterobiasis; Oxyuriasis)

By Richard D. Pearson, MD, Emeritus Professor of Medicine, University of Virginia School of Medicine

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Enterobiasis is an intestinal infestation by the pinworm Enterobius vermicularis, usually in children. Its major symptom is perianal itching. Diagnosis is by visual inspection for threadlike worms in the perianal area or the cellophane tape test for ova. Treatment is with mebendazole or albendazole.

Pinworm infestation is the most common helminthic infection in the US. Most cases occur in school-aged children, adults who care for children, or family members of an infected child.


Pinworm infestation usually results from transfer of ova from the perianal area to fomites (clothing, bedding, furniture, rugs, toys, toilet seats), from which the ova are picked up by the new host, transmitted to the mouth, and swallowed. Thumb sucking is a risk factor. Reinfestation (autoinfestation) easily occurs through finger transfer of ova from the perianal area to the mouth. Pinworm infections have also been attributed to anilingus among adults.

Pinworms reach maturity in the lower GI tract within 2 to 6 wk. The female worm migrates out of the anus to the perianal region (usually at night) to deposit ova. The sticky, gelatinous substance in which the ova are deposited and the movements of the female worm cause perianal pruritus. The ova can survive on fomites as long as 3 wk at normal room temperature.

Symptoms and Signs

Most infected people have no symptoms or signs, but some experience perianal pruritus and develop perianal excoriations from scratching. Rarely, migrating female worms ascend the human female genital tract, causing vaginitis and, even less commonly, peritoneal lesions.

Many other conditions (eg, abdominal pain, insomnia, seizures) have been attributed to pinworm infestation, but a causal relationship is unlikely. Pinworms have been found obstructing the appendiceal lumen in cases of appendicitis, but the presence of the parasites may be coincidental.


  • Examination of the perianal region for worms, ova, or both

Pinworm infestation can be diagnosed by finding the female worm, which is 8 to 13 mm long (males are 2 to 5 mm), in the perianal region 1 or 2 h after a child goes to bed at night or in the morning or by using a low-power microscope to identify ova on cellophane tape. The ova are obtained in the early morning before the child arises by patting the perianal skinfolds with a strip of cellophane tape, which is then placed sticky side down on a glass slide and viewed microscopically. The 50 by 30 μm ova are oval with a thin shell that contains a curled-up larva. A drop of toluene placed between tape and slide dissolves the adhesive and eliminates air bubbles under the tape, which can hamper identification of the ova. This procedure should be repeated on 3 successive mornings if necessary.

Eggs may also be encountered, but less frequently, in stool, urine, or vaginal smears.


  • Mebendazole, albendazole, or pyrantel pamoate

Because pinworm infestation is seldom harmful, prevalence is high, and reinfestation is common, treatment is indicated only for symptomatic infections. However, most parents actively seek treatment when their children have pinworms.

A single dose of any of the following, repeated in 2 wk, is effective in eradicating pinworms (but not ova) in > 90% of cases:

  • Mebendazole 100 mg po (regardless of age)

  • Albendazole 400 mg po

  • Pyrantel pamoate 11 mg/kg (maximum dose of 1 g) po

Carbolated petrolatum (ie, containing carbolic acid) or other antipruritic creams or ointments applied to the perianal region may relieve itching.


Pinworm reinfestation is common because viable ova may be excreted for 1 wk after therapy, and ova deposited in the environment before therapy can survive 3 wk. Multiple infestations within the household are common, and treatment of the entire family may be necessary.

The following can help prevent the spread of pinworm:

  • Washing the hands with soap and warm water after using the toilet, after changing diapers, and before handling food (the most successful way)

  • Frequently washing clothing, bedding, and toys

  • If people are infected, showering every morning to help remove eggs on the skin

  • Vacuuming he environment to try to eliminate eggs

Key Points

  • Pinworm infestation is the most common helminthic infection in the US; most cases occur in school-aged children, in adults who care for children, or in family members of an infected child.

  • Pinworm infestation is seldom harmful, and reinfestation is common.

  • Ova deposited in the environment can survive 3 wk.

  • Pinworm eggs may be ingested when people touch their mouth after they scratch their perianal area or after they handle contaminated clothes or other objects (eg, bed linens).

  • Most infected people have no symptoms or signs, but some experience perianal pruritus.

  • Diagnose pinworm infestation by collecting ova in the morning on cellophane tape and using a low-power microscope to identify them; diagnosis can also be made by finding the female worm in the perianal region 1 or 2 h after a child goes to bed at night.

  • If patients have symptomatic infections, treat with mebendazole, albendazole, or pyrantel pamoate.

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