Enterobiasis (Pinworm Infestation) 

Updated: Nov 23, 2021
Author: Wayne Wolfram, MD, MPH; Chief Editor: Russell W Steele, MD 


Practice Essentials

Enterobiasis (also known as pinworm infestation) is caused by the small nematode Enterobius vermicularis. (See the image below.) This common helminthic infestation has an estimated prevalence of 40 million infected individuals in the United States.[1]  The female nematode averages 10 mm × 0.7 mm, whereas males are smaller. All socioeconomic levels are affected. Infestation often occurs in family clusters. Infestation does not equate with poor home sanitary measures (an important point when discussing therapy).

Pinworms in a young patient. Pinworms in a young patient.

Signs and symptoms of enterobiasis

Patients are often asymptomatic. Pinworms may be incidentally discovered when they are seen in the perineal region. If patients are symptomatic, pruritus ani and pruritus vulvae are common presenting symptoms.

See Presentation for more detail.

Diagnosis of enterobiasis

Eggs are usually deposited in great quantities on the perineum at night. The diagnosis is made by identifying eggs under the low-power lens of a microscope.

See Workup for more detail.

Management of enterobiasis

An antihelminthic medication should be prescribed to patients with pinworm infestation. Application of an antipruritic ointment or albendazole may help control itching and scratching.[2]

Thorough handwashing can deter transmission.

See Treatment and Medication for more detail.


E vermicularis is an obligate parasite; humans are the only natural host. Fecal-oral contamination via hand-mouth contact or via fomites (toys, clothes) are common methods of infestation. After ingestion, eggs usually hatch in the duodenum within 6 hours. Worms mature in as little as 2 weeks and have a life span of approximately 2 months.

Adult worms normally inhabit the terminal ileum, cecum, vermiform appendix, and proximal ascending colon. The worms live free in the intestinal lumen. Little evidence supports invasion of healthy tissue under normal conditions. The female worm migrates to the rectum after copulation and, if not expelled during defecation, migrates to the perineum (often at night) where an average of 11,000 eggs are released. Eggs become infectious within 6-8 hours and, under optimum conditions, remain infectious in the environment for as long as 3 weeks.

See the image below.

Because of the short incubation time until the ova Because of the short incubation time until the ova are infectious, eggs that are deposited under the fingernails during scratching and then placed in the mouth may be a mode of reinfestation.


United States statistics

Prevalence is approximately 5-15% in the general population; however, this rate has declined in recent years. Prevalence rates are probably higher in institutionalized individuals. Humans are the only known host.

Infestation rate increases with increased population density, and with personal habits such as thumb sucking

International statistics

E vermicularis infestation occurs worldwide. Prevalence data vary by country.

A study that aimed to determine the extent of enterobiasis, strongyloidiasis, and other helminth infections in infants, preschool-aged, and school-aged children from rural coastal Tanzania reported that E vermicularis infestations were found in 4.2% of infants, 16.7%, of preschool-aged children, and 26.3% of school-aged children.[3]  

A study of kindergarten students in the Republic of the Marshall Islands found that the overall prevalence of E vermicularis infestation was 22.4%. The prevalence was higher among boys (24.5%) than among girls (20.31%) in the study.[4]

Infestation rates increase with increased population density and with certain personal habits like thumb-sucking.[5, 6]

Race-, sex-, and age-related demographics

All races are subject to infestation.

Infestation can occur in males and females.

The people most likely to be infected with pinworms are children younger than 18 years, people who take care of infected children, and people who are institutionalized. In these groups, the prevalence can reach 50%.[1]  However, individuals can be affected regardless of age or health status.


The prognosis is excellent, but reinfestation is common.


Secondary bacterial skin infection may develop from vigorous scratching to relieve pruritus. Reinfestation is common. Infection can develop as long as female pinworms continue to lay eggs on the skin. Restless sleeping may be due to pruritus ani. Infestation has been reported to cause enuresis.

Immunocompromised hosts

Although other helminthic infection rates are shown to be higher in patients with HIV, studies to date have not shown a statistically significant difference for E vermicularis.[7]


Beware of skin infection from vigorous scratching to relieve pruritus.

Pinworms have been associated with appendicitis,[8, 9]  nocturnal vaginal discharge,[10]  and inflammation of the female genital tract.[10]  However, small and large intestine ulcerations, perianal abscesses, intestinal pain, transient synovitis, and enuresis are believed to be coincidental and not causal.[11]

If a patient with enterobiasis is refractory to treatment, consider the possibility of an infestation with Dipylidium caninum, which is a common tapeworm that infects domestic cats and dogs.[12]

Patient Education

Inform families that dogs and cats do not harbor E vermicularis.

Inform families that infestation may occur in spite of proper child and household hygiene.

Counsel families to avoid overreaction through aggressive sanitary measures. Because infectious eggs may be in bedclothes and dust and remain infectious for 20 days, wet-mopping floors or vacuuming carpets and washing bedclothes are prudent precautions.

Reassuring families that pinworms are not a sexually transmitted disease and are not evidence of child abuse may be helpful.

Keeping the patient's fingernails trimmed to prevent excoriations is helpful.

Avoid scratching the area and nail biting because this is a cause of autoinfection.

Encourage the patient to bathe in the morning; this significantly reduces the number of eggs.

Children may return to school once they have received a dose of medication, bathed, and have nails trimmed.

Bed linens should be washed in hot, soapy water.




Patients with enterobiasis are often asymptomatic. Worms may be incidentally discovered when they are seen in the perineal region.

If patients are symptomatic, pruritus ani and pruritus vulvae are common presenting symptoms.

Restlessness during sleep is noted by the parents of many patients.

Enuresis may be a symptom in children with pinworms.

Physical Examination

Patients often have excoriation or erythema of the perineum, vulvae, or both, but infestation can occur without these signs.

Visual sighting of a worm by a reliable source (eg, a parent) is usually accepted as evidence of infestation and grounds for treatment.

Worms can be found in stools or on the patient's perineum before bathing in the morning.

Occasionally, the gravid female worm may aberrantly migrate into the female genitalia and produce vaginitis.[13]  Incidental recovery at necropsy or surgery of small granulomatous lesions surrounding the worm, larvae, or eggs in the salpinx and peritoneum demonstrates the worm's ability to ascend the female genital tract.

Abdominal pain may sometimes be severe and can mimic acute appendicitis.[14]





Laboratory Studies

Without a visual report, diagnosis of enterobiasis can be confirmed using the knowledge that eggs are normally deposited in great quantities on the perineum at night.

Wide (2 inch) transparent tape is pressed against the perineum at night or in the morning before the patient bathes to capture eggs.[15] Three such specimens are usually consecutively collected.

Diagnosis is made by identifying eggs under the low-power lens of microscope. Dilute sodium hydroxide or toluene should be added to the slide.

Imaging Studies

Imaging studies are not indicated.



Approach Considerations

An antihelminthic medication should be prescribed to patients with enterobiasis.

Application of an antipruritic ointment or albendazole may help control scratching.[2]

Thorough handwashing can deter transmission.

Medical Care

Fear, disgust, and guilt are common parental reactions to a parasitic worm infestation, such as enterobiasis. Many families present to the emergency department or their pediatrician with misconceptions about pinworms. In addition to prescribing medications, educating families about pinworms (see Patient Education) is helpful.

Thorough and regular handwashing is effective in preventing disease transmission.

Changing personal habits such as thumb-sucking or nail-biting may reduce re-infection.



Medication Summary

Mebendazole is not currently available in the United States. Pyrantel pamoate or albendazole (not currently approved for this use by the US Food and Drug Administration) are recommended alternatives. A second dose given 2 weeks after the initial dose is recommended.[16]

Because asymptomatic infestation of other members in a household is frequent, simultaneously treating all household members may be reasonable. Families should be informed that repeat infestations are common. Reinfestation is treated with the same medications as the initial infestation.

Symptomatic relief of pruritus can be obtained by applying an antipruritic ointment or cream topically to the affected (usually perianal) region.

Anal albendazole may help with symptoms of pruritus ani. A recent letter to the editor stated a “local application of albendazole using an ear bud soaked with the residual albendazole suspension in the vial” in addition to the recommended oral dose of albendazole provided dramatic relief of pruritus ani.[2]

Ivermectin has been shown to have decreased efficacy as a single agent, compared with albendazole.[17] However, it may possess efficacy when given as an adjunct.




Class Summary

Parasite biochemical pathways are different from the human host, thus toxicity is directed to the parasite, egg, or larvae. Mechanism of action varies within the drug class.

Pyrantel pamoate (Pamix, Reeses Pinworm Medicine, Pin-X)

Depolarizing neuromuscular blocking agent and inhibits cholinesterases, resulting in spastic paralysis of the worm. Purging not necessary. May be taken with milk or fruit juices.


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

Albendazole (Albenza)

A benzimidazole carbamate drug that inhibits tubulin polymerization, resulting in degeneration of cytoplasmic microtubules. Decreases ATP production in worm, causing energy depletion, immobilization, and finally death. Converted in the liver to its primary metabolite, albendazole sulfoxide. Less than 1% of the primary metabolite is excreted in the urine. Plasma level is noted to rise significantly (as much as 5-fold) when ingested after high-fat meal. Experience with patients < 6 y is limited.

To avoid inflammatory response in CNS, patient must also be started on anticonvulsants and high-dose glucocorticoids.