Fast Five Quiz: Drowning and Water-Related Health Concerns

Richard H. Sinert, DO


May 13, 2022

The traditional basis of diagnosis is identification of Giardia intestinalis trophozoites or cysts in the stool of infected patients via a stool ova and parasite (O&P) examination. It remains the diagnostic method with which other tests are compared. Stool antigen enzyme-linked immunosorbent assays are also available. These tests are similar to the stool O&P test in terms of cost and have a high sensitivity and specificity. They are best used as a screening test but should not take the place of stool microscopy. Because the differential for giardiasis includes other parasitic diseases, stool microscopy should be routinely performed.

Approximately half of individuals with giardiasis are asymptomatic. For those in which symptoms do occur, the onset is typically 1-2 weeks after infection. Clinical signs and symptoms of giardiasis include:

  • Diarrhea

  • Malaise, weakness

  • Abdominal distention

  • Flatulence

  • Abdominal cramps

  • Nausea

  • Malodorous, greasy stools

  • Anorexia

  • Weight loss

  • Vomiting

  • Low-grade fever (infrequent)

  • Various neurologic symptoms (eg, irritability, sleep disorder, mental depression, neurasthenia)

  • Urticaria

Standard treatment for giardiasis consists of antibiotic therapy. Metronidazole is the most commonly prescribed antibiotic for this condition. However, metronidazole use has been associated with significant failure rates in clearing parasites from the gut and with poor patient compliance. Generally, do not treat asymptomatic persons who excrete the organism, except to prevent household transmission (eg, from toddlers to pregnant women or to patients with hypogammaglobulinemia or cystic fibrosis) and to permit adequate treatment in individuals with possible G intestinalis–associated antibiotic malabsorption who require oral antibiotic treatment for other infections.

Learn more about giardiasis.


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