Pinworm (Enterobiasis)

Updated: Feb 10, 2023
  • Author: Sun Huh, MD, PhD; Chief Editor: Michael Stuart Bronze, MD  more...
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Pinworm infection, also called enterobiasis, is caused by Enterobius vermicularis, a white slender nematode with a pointed tail. In humans, they reside in the cecum, appendix, and ascending colon. Female pinworms are 8-13 mm long, and males are 2-5 mm long. [1, 2]

Pinworm infection is primarily a pediatric condition, and parents are typically infected via transmission through their children. Pinworm is prevalent throughout the temperate regions of the world and is the most common helminthic infection in the United States. [2, 3]

Transmission can occur via direct contact with contaminated furniture, bedclothes, bedding, towels, toilets, doorknobs, or other objects. The parasite also can be transmitted during sexual contact. [1, 2]

Pinworm infection generally is asymptomatic; asymptomatic carriers are common. [1, 2]

The cure rate with treatment is 90-95%. Re-infection is common, especially if all contacts are not treated simultaneously.

Adult female worms of Enterobius vermicularis coll Adult female worms of Enterobius vermicularis collected from a 2-year-old girl in a Korean orphanage after treatment with pyrantel pamoate 10 mg/kg.
Pinworms in a young patient. Pinworms in a young patient.

Pathophysiology and Etiology

The primary symptoms of pinworm infection include pruritus or a prickling sensation in the perianal area, which is produced when a gravid female pinworm migrates to the anal area and inserts her tail pin into the mucosa for ovideposition, usually at nighttime. E vermicularis lives in the small intestines, primarily the ileocecal region.

The movement of the female and the ova cause intense local itching. Ova may survive for up to 3 weeks before hatching. The hatched larvae can then migrate back into the anus and lower intestine, causing retroinfection. Embryonated eggs may be released into the air or onto fomites (eg, bedding, clothing, toys, paper money) or onto hands and then placed directly into the mouth and swallowed (autoinfection), after which they settle in the small intestines. [1]

Pinworms that inhabit the cecum and adjacent areas typically cause no symptoms. Diarrhea due to inflammation of the bowel wall can occur during acute infection. Although pinworms have been found in the region of the appendix during histologic studies of acute appendicitis, the relationship most likely is incidental. [1, 4]

Risk factors for pinworms include living with a person who is egg-positive, eating before washing hands, and poor personal or group hygiene. [1]



E vermicularis is the most common helminthic infestation in the United States. General prevalence in children is reported to be 0.2-20%. Pinworm infection is most common in persons who live in crowded living conditions and in individuals who are institutionalized. [1] Prevalence in institutionalized persons is reported to be 50-100%. A similar prevalence of pinworm infestation has been reported in European countries. [5]

The general prevalence of pinworm infection in some regions may be as high as 12%. Pinworm infection is most common in cosmopolitan areas in cool and temperate regions. Egg carrier rates vary by country, from 0.1-98.4%.

Of all age groups, school-aged children are most at risk for pinworm infections. In adults, pinworm infection is most common in parents aged 30-39 years, typically owing to transmission from their children aged 5-9 years.

Overall, males are affected twice as often as females, except in people aged 5-14 years, when infection is predominantly in females. [1]



Pinworm infection does not cause severe morbidity unless ectopic infection occurs. This rare complication occurs in individuals with conditions that compromise the integrity of the bowel wall (eg, inflammatory bowel disease). Parasites migrate through the bowel wall and are found in extracolonic sites.

Ectopic enterobiases have been described in various locations, including the vagina, salpinx, inguinal area, genital area, pelvic peritoneum, omentum, liver, salivary glands, male genital tract, and even the lungs. They also have been associated with acute appendicitis, eosinophilic colitis, and eosinophilic gastroenteritis. [1, 6]

Pinworm infestation is very rarely fatal; death and morbidity are from secondary infection. A 28% to 68% increased risk for appendicitis is associated with pinworm infestation. [4]

Eradicating pinworm in groups of institutionalized persons is difficult. Continuous follow-up examination is necessary.

Therapy is much more effective if the child's family and classmates are treated at the same time.



Some case reports have suggested that severe pinworm infection may be associated with an increased risk for appendicitis. [3]

Scratching the itchy area may cause eczema or a bacterial infection around the rectum. In girls, pinworm infection can spread to the vagina and may cause a vaginal discharge.

E vermicularis can mimic other disease processes and, although rare, can lead to serious infectious complications such as tubo-ovarian abscesses. [7]

The following complications have also been noted: appendicitis, endometritis, salpingitis, urethritis, urinary tract infection, and vulvovaginitis.


Patient Education

Focus on handwashing, especially before eating. Strict handwashing should be completed after using the toilet or changing a diaper of an affected baby. [1]

Washing sheets, clothes, and towels in a washing machine using regular laundry soap can eliminate pinworm eggs. All bedding and toys should be cleaned every 3-7 days for 3 weeks. Underwear and pajamas should be washed daily for 2 weeks. [1]