Giardiasis

Key Features

Essentials of Diagnosis

• Chronic relapsing diarrhea, flatulence, bloating, anorexia, poor weight gain

• No fever or hematochezia

• Detection of trophozoites, cysts, or Giardia antigens in stool

General Considerations

• Caused by Giardia intestinalis (formerly Giardia lamblia)

• Associated with drinking contaminated water, either in rural areas or in areas with faulty purification systems

• Fecal-oral contamination allows person-to-person spread

• Day care centers are a major source of infection

• Food-borne outbreaks also occur

• May occur at any age, although infection is rare in neonates

Clinical Findings

• No symptoms occur in 25% of infected persons

• Infection is followed by either asymptomatic cyst passage, acute self-limited diarrhea, or a chronic syndrome of diarrhea, malabsorption, and weight loss

• Acute diarrhea occurs 1–2 weeks after infection and is characterized by

  • Abrupt onset of diarrhea with greasy, malodorous stools

  • Malaise

  • Flatulence

  • Bloating

  • Nausea

• Fever and vomiting are unusual

• Disease has a protracted course (> 1 week) and frequently leads to weight loss

• Can be a self-limited infection in some patients, and in others cause chronic symptoms

• Patients in whom chronic diarrhea develops complain of

  • Profound malaise

  • Lassitude

  • Headache

  • Diffuse abdominal pain in association with bouts of diarrhea—most typically foul-smelling, greasy stools

• Chronic diarrhea frequently leads to malabsorption, steatorrhea, vitamins A and B₁₂ deficiencies, and disaccharidase depletion.

• Lactose intolerance

  • Develops in 20–40% of patients

  • Can persist for several weeks after treatment

  • Needs to be differentiated from relapsing giardiasis or reinfection

Diagnosis

• Antigen detection by means of ELISAs, nonenzymatic immunoassays, and direct fluorescence antibody tests

  • Standard diagnostic tests in the United States

  • Have a more rapid return of results

  • More sensitive and specific than stool ova and parasite examination

• In resource-poor areas without access to antigen tests, finding the parasite in stool confirms diagnosis

• Liquid stools have the highest yield of trophozoites

• With semiformed stools, the examiner should look for cysts in fresh or fixed specimens, preferably using a concentration technique

  • One examination has a sensitivity of 50–70%

  • Three examinations increase the sensitivity to 90%

• Direct sampling of duodenal aspirates or biopsy is restricted to particularly difficult cases

Treatment

• Metronidazole, tinidazole, and nitazoxanide are the drugs of choice

• Metronidazole

  • Dosage: 5 mg/kg (up to 250 mg) three times a day for 5–7 days

  • Has 80–95% efficacy

  • Well tolerated in children

• Tinidazole has an efficacy approaching 90% when given as a single dose of 50 mg/kg (up to 2 g)

• Nitazoxanide

  • Available in liquid formulation and requires only 3 days of treatment

  • Recommended doses

    • 100 mg (5 mL) every 12 hours for children 12–47 months of age

    • 200 mg every 12 hours for 4- to 11-year-olds

    • 500 mg every 12 hours for children 12 years or older

• For patients who do not respond to therapy, or are reinfected, a second course with the same drug ...