Pinworm (Enterobiasis)

Updated: Feb 10, 2023
Author: Sun Huh, MD, PhD; Chief Editor: Michael Stuart Bronze, MD 



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]



History and Physical Examination

The patient history of pinworm infection, also called enterobiasis, includes itching or prickling pain in the anal area (usually at nighttime or in the early morning), intense anal itching, restless sleep or difficulty sleeping, and, rarely, abdominal discomfort or loss of appetite.[8] Other symptoms include irritability and, in females, vaginal itching. Most patients, however, are asymptomatic.[1, 2]

Although a hospital-based study of children aged 2-12 years found that perianal itching was not significantly more common in children who are infected than in children who are uninfected, persons who are Enterobius egg–positive typically visit a physician because of perianal itching.[1, 2]

The pale-colored female pinworm (10 mm) may be seen in the perianal region with the naked eye. The worm's appearance is easily confused with bits of cotton thread. Eggs (30 μm X 50-60 μm) usually are not seen without a microscope. Perianal excoriations secondary to scratching may be found.[1, 2]



Diagnostic Considerations

The diagnostic process usually is completed after hearing the symptoms of the infected person, including perianal itching, perianal pain,  insomnia, or diarrhea.

Diarrhea can be seen in the early stage of the pinworm infection. Diagnosis is based on the detection of eggs after the perianal swab with cellotape. However, the egg negative finding does not always indicate non-infection, because the false negative rate is high. The egg positive finding means that one female worm died after ovulation at the perianal area.  If a male worm stays in the caecum, it can not be detected. Also, if female worms are present in the large intestine, but do not migrate to the perianal area, eggs can not be detected. Therefore for more accurate diagnosis, repeat examination is required. If the worm burden is high, there is a chance of egg positive at the single exam. However, if the worm burden is low, the repeat exam is helpful for the diagnosis.[1, 2]

Differential Diagnoses



Approach Considerations

Glass slide microscopic analysis for Enterobius vermicularis may be performed looking for ova and female pinworms. A specimen is best obtained by dabbing the stretched, unwashed perianal folds in the early morning with cellophane tape and affixing the specimen onto a slide. A negative test for 5 consecutive mornings effectively rules out the diagnosis.[1, 2]

Microscopic examination shows the elongated ovoid egg distinctly compressed laterally and flattened on one side. The egg measures 50-60 µm X 20-30 µm and contains larva.

In areas where pinworms are endemic, consider analyzing any removed appendiceal stump for infestation.[9]

Patients with recurrent episodes of perianal itching should have a stool sample sent to the laboratory for analysis because different parasites, which require different treatment, may appear similar to E vermicularis using the cellophane-tape test.[2, 10]

Cellophane-tape Examination

A perianal cellophane swab or cellophane-tape examination should be used to detect Enterobius vermicularis eggs.[1, 2] Egg detection is associated with a false-positive rate of 5-11% and a false-negative rate of 70-95%.[11] One report found that a single cellophane-tape examination yielded a sensitivity of 50%, three examinations yielded a sensitivity of 90%, and five examinations yielded a sensitivity of 99%.

Microscopic view of Enterobius vermiculariseggs at Microscopic view of Enterobius vermiculariseggs attached to cellophane tape after a perianal swab from a child in kindergarten in Seoul, Korea. Egg size was 50-60 μm X 20-30 μm. The eggs are elongated and ovoid, distinctly compressed laterally, and flattened on one side.


Approach Considerations

Anthelmintics, such as mebendazole, pyrantel pamoate, and albendazole, are active against Enterobius vermicularis. Itching, irritation, and excoriation should be treated symptomatically. Reinfection with E vermicularis immediately after the completion of drug therapy is common. Additionally, young pinworms may be resistant to drugs.[12] Successful eradication of pinworm infection, also called enterobiasis, requires two doses of medication - an initial dose followed by a subsequent dose 2 weeks later.[1, 2, 13]

All family members or classmates who are infected must be treated simultaneously. In addition, personal and group hygiene must be improved, individuals must wash their hands before eating, and children should be discouraged from activities such as finger-sucking.[2]

If large numbers of children attending the same school test positive for pinworm eggs, all classmates and family members of the children who are infected should be treated 2 times at 2-week intervals. If less than 30% of class members test positive for pinworm eggs, treating only the children who have positive test results reduces the positive rate for eggs in that class. Follow-up is recommended if the pinworm symptoms persist longer than 2 weeks or if signs of bacterial superinfection occur.[1, 2]

If a general physician is unsure how to care for persons with pinworm infection, a parasitologist should be consulted. If no parasitologist is available, a pediatrician or infectious disease specialist should be consulted instead.

Long-Term Monitoring

Patients with pinworm infection must undergo follow-up examination to evaluate for reinfection after anthelmintic treatment is completed.

Although the first single examination may be negative for Enterobius eggs, a follow-up perianal swab is necessary if perianal itching or prickling pain persists.


To prevent reinfection, patient and family hygiene must be improved, and individuals must be certain to wash their hands before eating. At-risk individuals should bathe upon waking to help reduce the possibility of egg contamination. Children should be discouraged from activities such as sucking their fingers and scratching bare anal areas.[1, 2]

The entire household should be treated simultaneously. Treatment is much more effective if the child's family and classmates are treated at the same time. Washing sheets, clothes, and towels in a washing machine using regular laundry soap can eliminate pinworm eggs.[1]

For clinicians treating infected patients, strict handwashing is required after contact with the patient, patient’s clothing, and stretcher. All bedding and gowns should be cleaned. In addition, stretchers should be washed before further patient use.


Because pinworm eggs may become airborne, it is difficult to prevent the infection if it occurs in a group such as kindergartens, primary schools, and orphanages. Furthermore, the family members can be infected easily if any one member is infected. Thefore, treatment of the group or family is necessary for the prevention of further transmission. Personal hygiene, including hand-washing after the defecation and before meals is the best personal preventive method. Frequent cleaning of the space is the best way to prevent the transmission of E vermicularis egg in a group environment.[1]



Medication Summary

The goals of pharmacotherapy are to eradicate the infestation, reduce morbidity, and prevent complications. It is important to empirically cover the entire household simultaneously for pinworms when a decision is made to treat. Anthelmintics, such as mebendazole, pyrantel pamoate, and albendazole, are active against Enterobius vermicularis. Itching, irritation, and excoriation should be treated symptomatically.[1, 2]

Reinfection with E vermicularis immediately after the completion of drug therapy is common. Additionally, young pinworms may be resistant to drugs.[12] Successful eradication of pinworm infection, also called enterobiasis, requires two doses of medication - an initial dose followed by a subsequent dose 2 weeks later.[1, 2, 13]


Class Summary

Parasite biochemical pathways are sufficiently different from the human host to allow selective interference by chemotherapeutic agents in relatively small doses.


Mebendazole causes worm death by selectively and irreversibly blocking uptake of glucose and other nutrients in susceptible adult intestine where helminths dwell.

Pyrantel pamoate (Reese's Pinworm Medicine, Pin-X)

Pyrantel pamoate is a depolarizing neuromuscular blocking agent. It inhibits cholinesterases, resulting in spastic paralysis of the worm.

Albendazole (Albenza)

Albendazole decreases ATP production in worms, causing energy depletion, immobilization, and, finally, death. To avoid inflammatory responses in the CNS, patients must also be started on anticonvulsants and high-dose glucocorticoids.


Questions & Answers