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By Marianne Belleza, R.N.

Giardiasis is a major diarrheal disease found throughout the world.

Table of Contents

What is Giardiasis?

Giardiasis is a major diarrheal disease found throughout the world.

  • The flagellate protozoan Giardia intestinalis­­ (previously known as G. lamblia or G. duodenalis), its causative agent, is the most commonly identified intestinal parasite in the United States and the most common protozoal intestinal parasite isolated worldwide.
  • Giardiasis usually represents a zoonosis with cross-infectivity between animals and humans.
  • G. intestinalis can cause asymptomatic colonization or acute or chronic diarrheal illness.
  • The organism has been found in as many as 80% of raw water supplies from lakes, streams, and ponds and in as many as 15% of filtered water samples.


Infection with Giardia intestinalis most often results from fecal-oral transmission or ingestion of contaminated water.

  • Person-to-person spread is common, with 25% of family members with infected children themselves becoming infected.
  • Giardia has one of the simplest life cycles of all human parasites; the life cycle is composed of 2 stages: (1) the trophozoite, which exists freely in the human small intestine; and (2) the cyst, which is passed into the environment.
  • Upon ingestion of the cyst (see the second image below), contained in contaminated water or food, excystation occurs in the stomach and the duodenum in the presence of acid and pancreatic enzymes.
  • The trophozoites pass into the small bowel where they multiply rapidly, with a doubling time of 9-12 hours; as trophozoites pass into the large bowel, encystation occurs in the presence of neutral pH and secondary bile salts.
  • Cysts are passed into the environment, and the cycle is repeated.

Statistics and Incidences

Giardia remains the parasite most commonly identified in stool specimens, causing about 1.2 million annual episodes of illness.

  • From 1964-1984, G lamblia caused at least 90 water-borne outbreaks of diarrhea, affecting more than 23,000 people; these outbreaks typically involved small water systems using untreated or inadequately treated surface water.
  • The incidence of giardiasis is high among individuals who camp and backpack in mountainous Western states.
  • Other groups at increased risk for infection include children, homosexual men, and individuals with immunoglobulin deficiency states (inherited or acquired).
  • Yoder et al reported that the incidence is greatest in northern states, but this may be related to the differences in individual state surveillance systems and may not necessarily reflect an actual higher incidence.
  • Endemic infection occurs most commonly from July through October among children younger than 5 years and adults aged 25-39 years.
  • Carrier rates as high as 30-60% have been documented among children in day care centers, institutions, and on Native American reservations.
  • The asymptomatic carriage rate in children may be as high as 20% in southern regions and in children younger than 36 months who attend daycare centers.
  • In the 46 states reporting giardiasis, the mean number of cases per 100,000 population varies by state, with a range of 0.1-23.5 cases; most cases are reported between June and October and are associated with the summer recreational water season and camping.
  • Giardia has a worldwide distribution, occurring in both temperate and tropical regions.
  • Prevalence rates vary from 4-42%; in the industrialized world, overall prevalence rates are 2-5%.
  • In the developing world, G. intestinalis infects infants early in life and is a major cause of epidemic childhood diarrhea; prevalence rates of 15-20% in children younger than 10 years are common.
  • Giardiasis does not have any race predilection; Native American populations residing on reservations can have high carrier rates.
  • Giardiasis is slightly more common in males than in females; a Canadian population study demonstrated infection rates of 21.2 per 100,000 per year versus 17.9 per 100,000 per year for males and females, respectively, resulting in a relative risk of 1.19.
  • According to 2003–2005 data from the Centers for Disease Control and Prevention, the greatest number of reported cases occurred among children aged 1-4 and 5-9 years and adults aged 35-44 years.


Giardiasis is caused by the flagellate protozoan Giardia intestinalis (formerly known as G lamblia).

  • Person to person transmission. Person-to-person transmission, often associated with poor hygiene and sanitation, is a primary means of infection; diaper changing and inadequate hand washing are risk factors for transmission from infected children;  children attending day care centers, as well as day-care workers, have a higher risk of infection secondary to fecal-oral transmission.
  • Water-borne transmission. Water-borne transmission is responsible for a significant number of epidemics in the United States, generally following ingestion of unfiltered surface water; Giardia cysts retain viability in cold water for as long as 2-3 months.
  • Venereal transmission. Venereal transmission occurs through fecal-oral contamination; food-borne epidemics have been reported, most commonly secondary to contamination by infected food-handlers.

Clinical Manifestations

Clinical signs and symptoms of giardiasis include the following:

  • Diarrhea. Diarrhea is the most common symptom of acute Giardia infection, occurring in 90% of symptomatic subjects; marked or moderate partial villous atrophy in the duodenum and jejunum can be observed in histologic sections from asymptomatic individuals who are infected; in addition to disrupting the mucosal epithelium, effects in the intestinal lumen may contribute to malabsorption and the production of diarrhea.
  • Malaise, weakness. Malaise or weakness occurs due to loss of electrolytes with diarrhea.
  • Abdominal distention. Abdominal cramping, bloating, and flatulence occurs in 70-75% of symptomatic patients.
  • Malodorous, greasy stools. Stools become malodorous, mushy, and greasy.
  • Anorexia and weight loss. Anorexia, fatigue, malaise, and weight loss are common; weight loss occurs in more than 50% of patients and averages 10 pounds.

Assessment and Diagnostic Findings

The traditional basis of diagnosis is the identification of Giardia intestinalis trophozoites or cysts in the stool of infected patients via a stool ova and parasite (O&P) examination.

  • Stool examination. Stool examination for trophozoites or cysts is the traditional method for diagnosing giardiasis; at least 3 stools taken at 2-day intervals should be examined for ova and parasites; trophozoites may be found in fresh, watery stools but disintegrate rapidly.
  • Stool antigen detection. Several tests to detect Giardia antigen in the stool are commercially available; these utilize either an immunofluorescent antibody (IFA) assay or a capture enzyme-linked immunosorbent assay (ELISA) against cyst or trophozoite antigens; these tests have a sensitivity of 85-98% and a specificity of 90-100%.
  • String test. The string test (Entero-test) consists of a gelatin capsule containing a nylon string with a weight attached to it; the patient tapes one end of the string to his or her cheek and swallows the capsule; after the gelatin dissolves in the stomach, the weight carries the string into the duodenum; the mucus from the string is examined for trophozoites in an iodine or saline wet mount or after fixation and staining.

Medical Management

Standard treatment for giardiasis consists of antibiotic therapy.

  • Fluid therapy. Appropriate fluid and electrolyte management is critical, particularly in patients with large-volume diarrheal losses.
  • Diet. No special diet is required; a significant portion of patients have symptoms of lactose intolerance (cramping, bloating, diarrhea), and maintenance on a lactose-free diet for several months may be helpful.
  • Activity. Activity restrictions are not indicated; however, infected subjects who are at risk of spreading the infection should be isolated and treated

Pharmacologic Management

Antibiotic therapy is standard in the treatment of giardiasis.

  • Antibiotics. The 2 major classes of drugs that have proven benefit in the treatment of giardiasis are nitroimidazole derivatives and acridine dyes; although most experts recommend metronidazole and tinidazole as the drugs of choice because the brief treatment periods encourage good patient adherence, treatment failures occur in as many as 20% of cases, probably because of resistance; therefore, treatment with a second-line drug (eg, mepacrine) may be necessary.

Nursing Management

Nursing management of a child with giardiasis include the following:

Nursing Assessment

Nursing assessment of a child with giardiasis include:

  • History. The nature of the overall clinical manifestations in affected patients is influenced by numerous factors, including the parasite load, virulence of the isolate, and the host immune response.
  • Physical exam. Physical examination does not contribute to the diagnosis of giardiasis; weight loss may be evident, but no known unique physical findings are attributable to giardiasis.

Nursing Diagnosis

Based on the assessment data, the major nursing diagnoses are:

Nursing Care Planning and Goals

The major nursing care planning goals for patients with giardiasis are:

  • The client will maintain fluid and electrolyte balance.
  • The client’s pain will be lost or diminished.
  • The client will show an increased appetite, weight according to age.
  • The client will maintain normothermia indicated by the absence of signs and symptoms of hyperthermia.

Nursing Interventions

Nursing interventions for a child with giardiasis include the following:

  • Restore Fluid & Electrolyte balance. Weigh patient daily and note decreased weight; record number and consistency of stools per day; if desired, use a fecal incontinence collector for accurate measurement of output; monitor and record intake and output; note oliguria and dark, concentrated urine; discuss the importance of fluid replacement during diarrheal episodes.
  • Reduce pain or discomfort. Assess the extent and characteristics of pain; give a warm compress on the abdomen; teach the client and caregivers about methods to distract from the pain, and set a position that can reduce the pain.
  • Improve hyperthermia. Provide tepid sponge baths; administer antipyretics as prescribed.


Goals are met as evidenced by:

  • The client restored normal fluid and electrolyte balance.
  • The client’s pain was diminished.
  • The client showed an increased appetite, weight according to age.
  • The client maintained normothermia indicated by the absence of signs and symptoms of hyperthermia.

Documentation Guidelines

Documentation in a child with giardiasis include:

  • Individual findings, including factors affecting, interactions, nature of social exchanges, specifics of individual behavior.
  • Cultural and religious beliefs, and expectations.
  • Plan of care.
  • Teaching plan.
  • Responses to interventions, teaching, and actions performed.
  • Attainment or progress toward the desired outcome.
Marianne leads a double life, working as a staff nurse during the day and moonlighting as a writer for Nurseslabs at night. As an outpatient department nurse, she has honed her skills in delivering health education to her patients, making her a valuable resource and study guide writer for aspiring student nurses.

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