Pinworm Infection

Pinworm infection (enterobiasis) is caused by the intestinal nematode Enterobius vermicularis (threadworm). The commonest helminth infection of children in temperate regions; also frequent in tropical settings. Affects about 10 to 40 percent of children, mostly ages 5 to 10 years and in institutions; household clustering is typical.

• Life cycle: eggs are swallowed from contaminated fingers, bedding, clothes, dust or surfaces; larvae hatch in the small intestine and mature in the caecum and colon; gravid females migrate at night to the perianal skin to lay 10,000 eggs and die; eggs are infective within 4 to 6 hours and survive 2 to 3 weeks in the environment. Autoinfection by scratching and retroinfection are common. The cycle takes 2 to 6 weeks.
• Risk factors: school or nursery attendance, crowding, nail biting, thumb sucking, poor hand hygiene, sharing bedding.
• Complications are uncommon: vulvovaginitis and urinary tract infection in girls, perianal dermatitis and secondary infection, rarely appendicitis (symptoms), salpingitis, peritonitis, granuloma.

• Perianal itching (pruritus ani), worse at night and early morning, disturbing sleep, with irritability, restless sleep and teeth grinding; scratching causes excoriation and secondary bacterial infection.
• Visible small white thread like worms (8 to 13 mm for the female) in the perianal area at night, in stool, or on underwear or bedding.
• Vulvovaginal itch and discharge in girls; dysuria; abdominal pain, nausea, reduced appetite; bedwetting.
• Many infections are asymptomatic.
• Red flags: right iliac fossa pain with fever (appendicitis), blood in stool, weight loss, persistent diarrhoea, haematuria, pelvic pain, persistent itching despite treatment and hygiene (different diagnosis), perianal lesions suggesting abuse, rash on the buttocks.

• Clinical diagnosis with visual identification of worms: inspect the perianal region at night with a torch (about 2 to 3 hours after the child falls asleep), or in the morning before washing.
• Adhesive cellophane tape test: press clear sticky tape to the perianal skin first thing in the morning before washing or toileting, transfer to a glass slide and examine under a microscope for characteristic eggs (50 to 60 micrometres, asymmetrical, with a flat side and larva inside); repeat on 3 consecutive mornings for about 90 percent sensitivity (single test about 50 percent).
• Stool microscopy is not useful (eggs rarely seen).
• Eosinophilia is uncommon. Colonoscopy may show worms incidentally.
• Differentials: threadworm like perianal itch from other causes (eczema, psoriasis, candida, scabies, fissures, haemorrhoids, streptococcal perianal dermatitis, poor hygiene, allergic contact dermatitis, anal warts, lichen sclerosus), vulvovaginitis.

• Treat the patient and all household members simultaneously, even if asymptomatic; reinfection is common.
• Drug therapy (a single dose followed by a repeat dose after 2 weeks to kill newly hatched worms from eggs that survived):
  • Mebendazole 100 mg orally as a single dose (children aged 2 years and over, and adults), repeated after 2 weeks.
  • Albendazole 400 mg orally as a single dose (age over 2 years and adults), repeated after 2 weeks.
  • Pyrantel pamoate 11 mg/kg orally (maximum 1 g) as a single dose, repeated after 2 weeks (licensed from age 6 months in some regions; not absorbed).
  • Infants aged under 2 years, and pregnant or breastfeeding women: hygiene measures alone for 6 weeks (avoid mebendazole and albendazole in the first trimester; if drug treatment is essential after the first trimester, mebendazole or pyrantel pamoate with specialist advice).
  • Side effects: abdominal pain, nausea, headache, transient liver enzyme rise (albendazole); mebendazole is contraindicated in known hypersensitivity.
• Hygiene (essential for 2 weeks after treatment, or 6 weeks if drugs are not used):
  • Wash hands with soap and water after the toilet, before meals and after nappy changes; scrub under short nails and discourage nail biting and thumb sucking.
  • Bathe or shower each morning to remove eggs, with attention to the perianal area; change underwear daily.
  • Wash bed linen, nightwear and towels at 60 C on the day of treatment; vacuum bedrooms; damp dust surfaces; keep toothbrushes covered.
  • Wear close fitting underwear at night; apply barrier cream or petroleum jelly to the perianal area to reduce itch.
• Itch relief: zinc oxide or hydrocortisone 1 percent cream for a few days to the perianal skin if inflamed; treat secondary infection with mupirocin 2 percent ointment twice daily for 5 days.
• Recurrent infection: reinforce hygiene and treat all contacts; consider nursery or school clusters.
• Follow up if symptoms persist after 4 weeks; reconsider diagnosis if the tape test remains negative.