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5-year-old Willow arrives in the ED at 3 a.m. 

Her mum says she has been waking up screaming on the last few nights, clutching her vulval area and saying it hurts.

Her parents have noticed she is scratching her bottom a lot, too, and they’ve had an email from school saying there are cases of threadworms in the reception class.

Threadworms (Enterobius vermicularis, also known as pinworms or seatworms) are the most common helminthic infection in the Western World. One thousand million individuals worldwide are infected, and threadworms are frequently seen in younger children – particularly those attending childcare and school settings.

How do you get threadworms?

Threadworms spread via the faecal-oral route. They lay their eggs in the perianal area. These are then picked up when the child scratches. They end up underneath fingernails and are then swallowed or transmitted by hand-to-hand contact to other children and adults who are in close contact with them. Threadworms can also be spread via fomites such as toothbrushes, toys, towels, and bedding. The average lifespan of the threadworm is two weeks.

What are the symptoms of threadworms?

Children classically present with an intensely itchy bottom. It is not uncommon for girls to become extremely distressed at night when the threadworms leave the anus and crawl onto the perineum, causing itching and irritation. Parents may be surprised and horrified if they take a torch in the darkened bedroom and spot small white wiggling creatures rapidly disappearing from the vulval area into the child’s anus. This history will clinch the diagnosis. 

Adults are not immune from picking up thread worms from their own or other people’s children, and it is not uncommon for the entire family to be symptomatic with perianal itching and/or night-time vulval pain.

You take a careful history from Willow’s mum and establish that she has been aware of Willow scratching her bottom for a few days.

Willow mentioned seeing “wiggly white things” in her poo the other day. 

Willow is normally fit and well. She has no past medical history. She is current with her immunizations, and the family has never travelled overseas. She lives with her parents in a terraced house with her older brother Jacob and two pet goldfish.

How do you make the diagnosis?

Diagnosis of threadworms is usually based on clinical history. You can ask parents to perform the sticky tape test if there is any doubt.

Transparent sticky tape is applied to the perianal area first thing in the morning and then examined under a microscope to detect threadworm eggs. This is rarely needed in practice, as a history of itchy bottom or vulvovaginitis is usually enough. You don’t need to examine the stool.

How do you treat threadworms?

Treatment involves medication and lifestyle measures.

Parents should be encouraged to self-manage by buying over-the-counter medication from their pharmacy. In the UK, this is oral mebendazole. It is available as a suspension for younger children or as a chewable tablet for older children and adults. Mebendazole is not licensed for children under two years, though it is considered safe for infants over six months. The entire household should be treated, and treatment should be repeated after 14 days.

Mebendazole is contraindicated in babies aged under six months of age and in pregnant women. These patients need to be scrupulous about their hand hygiene. If the cycle of fecal-oral transmission can be broken after 14 days, patients should spontaneously clear their infestation.

Willow’s mum is reassured by your explanation that her daughter has threadworms.

She tells you she has also been struggling with vulval itching and is relieved to hear that mebendazole should resolve her symptoms.

She will treat the whole family but asks you if Willow and her brother are OK to go to school and if she needs time off work from her job as a social worker.

Public Health England guidance states that children should not be excluded from schools or childcare settings if they have threadworms. Proper hand hygiene should mean that adults are at lower risk of transmitting threadworms to other adults or vulnerable contacts.

Complications are extremely unusual, especially in developed nations where access to health care and treatment is readily available. Persistent perianal itching or vulvovaginitis is the most common sequelae seen in UK practice. There are cases in the literature of recurrent urinary tract infections, appendicitis, and weight loss due to severe infestations, but these are rare.

Selected references

Dunphy L, Clark Z, Raja MH. Enterobius vermicularis (pinworm) infestation in a child presenting with symptoms of acute appendicitis: a wriggly tale! BMJ Case Rep. 2017;2017. pii: bcr-2017-220473.


  • Dr Tara George. MBChB (Hons) Sheffield 2002, FRCGP, DCH, DRCOG, DFSRH, PGCertMedEd Salaried GP and GP Trainer, Wingerworth Surgery, Wingerworth, Derbyshire. GP Training Programme Director, Chesterfield and the Derbyshire Dales GP Speciality Training Programme. Out of Hours GP and supervisor, Derbyshire Health United. Early Years Tutor, Phase 1, Sheffield University Medical School. Mentor, GP-s peer mentoring service and Derbyshire GPTF new to practice scheme. External Advisor RCGP. Host Bedside Reading podcast. Pronouns: she/her When she's not doing doctory things Tara loves to bake, to read novels, run and take out some of that pent up angst in Rockbox classes.

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