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Key Features

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Essentials of Diagnosis
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  • Chronic relapsing diarrhea, flatulence, bloating, anorexia, poor weight gain

  • No fever or hematochezia

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

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General Considerations
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  • 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

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Clinical Findings

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  • 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

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Diagnosis

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  • 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

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Treatment

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  • 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 or switching to another drug is ...

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