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Pinworms (Enterobiasis)

BASICS

  • Definition: Intestinal infection by Enterobius vermicularis, marked by perineal/perianal itching, worse at night
  • Synonyms: Enterobiasis

EPIDEMIOLOGY

  • Predominant Age: 5–14 years
  • Prevalence: Most common helminthic infection in the U.S.; 20–42 million cases, ~30% of children globally
  • Pediatric Note: More common in children; reinfection frequent

ETIOLOGY & PATHOPHYSIOLOGY

  • Lifecycle: Ingestion → larvae mature in small intestine (1–2 months) → adults in colon/cecum/appendix → females migrate nocturnally to perianal area to lay eggs → local itching → scratching → auto-inoculation/reinfection
  • Morphology: Small white worms (2–13 mm)
  • Associated conditions: Appendicitis (rare but reported)

RISK FACTORS

  • Institutionalization, crowded conditions, poor hygiene
  • Warm climate
  • Handling contaminated clothing/bedding

PREVENTION

  • Hand hygiene after defecation
  • Short fingernails
  • Daily washing of anus/genitals (preferably shower)
  • Avoid scratching, finger-to-mouth/nose contact

DIAGNOSIS

History

  • Perianal/perineal itching (worse at night)
  • Vulvovaginitis, dysuria, rare abdominal pain
  • Insomnia, restlessness

Physical Exam

  • Inspect perianal area (early morning best) for worms

Differential Diagnosis

  • Pruritus ani, dermatitis, psoriasis, HPV, HSV, fungal/yeast, scabies, vaginitis, IBD

Diagnostic Tests

  • Adhesive tape test (best done on 3 consecutive mornings before bathing; 90% sensitivity)
  • Pinworm paddle, anal swabs, or scraping under fingernails (eggs)
  • Microscopy: Ova are asymmetric, flat-sided, 56×27 µm; direct visualization of adult female worm (~10 mm)
  • Stool O&P: Not helpful (only 10–15% positive)
  • Serology: Not available

TREATMENT

First Line

  • Albendazole: 400 mg PO once (adults/children >20 kg), repeat in 2 weeks; 200 mg PO if ≤20 kg
  • Mebendazole: 100 mg PO once, repeat in 2–3 weeks (adults/children >2 years); caution <2 years
  • Pyrantel pamoate: 11 mg/kg PO once (max 1 g), repeat in 2 weeks; caution <2 years
  • All household contacts should be treated.

Special Populations

  • Pregnancy: Avoid drug therapy if possible (all are Category C). If needed, treat in 3rd trimester only if necessary.
  • Breastfeeding: Mebendazole permitted

ONGOING CARE

  • No follow-up required unless symptoms recur
  • Reinfection is common—repeat dosing recommended
  • For refractory cases, repeat dosing every 2 weeks for 4–6 cycles (rare)

PATIENT EDUCATION

  • Take medication with food
  • Strict hand hygiene, especially after bowel movements
  • Clip fingernails; discourage scratching
  • Wash bedding/clothes after diagnosis; do not shake linens
  • No sharing of washcloths; avoid cobathing children during/2 weeks after treatment; prefer showers

PROGNOSIS

  • Drug therapy: ~90% cure rate
  • Asymptomatic carriers common
  • Reinfection frequent, especially in children

COMPLICATIONS

  • Secondary bacterial infection from scratching
  • Girls: vulvovaginitis, urethritis, endometritis, salpingitis, UTIs
  • Appendicitis (rare)
  • Rare: ectopic granulomas (pelvis, GU tract, appendix), intussusception

ICD-10 CODE

  • B80 Enterobiasis

CLINICAL PEARLS

  • Nocturnal or early-morning perianal itch/restless sleep in children is classic for pinworm
  • Treat all close contacts and retreat after 2 weeks to prevent recurrence
  • Adhesive tape test is gold standard (prefer 3 consecutive mornings)
  • Stool O&P not useful