Definition
A.Giardia intestinalis is the leading parasitic cause of diarrhea. Infestation can lead to malabsorption by coating large areas of the small bowel, particularly the lower duodenum and upper jejunum. Most people infected with G. intestinalis remain asymptomatic, and most infections are self-limited.
Incidence
A.Giardiasis has a worldwide distribution and is especially prevalent in the United States and overseas. It is common in areas where water supplies are contaminated by human sewage. The age-specific prevalence of giardiasis is highest in children 1 to 5 years and in adults 35 to 39 years of age. The peak onset occurs annually during early summer through early fall.
Pathogenesis
A.G. intestinalis is a flagellated protozoan. The infective form is the cyst. Humans are the principal reservoir of infection, but Giardia can infect dogs, cats, beavers, and other animals that can contaminate water with feces containing cysts.
B.People become infected either directly, by hand-to-mouth transfer of cysts from feces of an infected person (e.g., child care), or indirectly, by ingestion of fecal-contaminated water or food. Most community-wide epidemics result from contaminated water supplies.
C.The incubation period is 1 to 3 weeks, with an average of 7 to 10 days. The infective form is the cyst with infection limited to the small intestine and the biliary tract. Disease is communicable for as long as the infected person excretes cysts.
D.Symptoms may last 2 to 6 weeks in otherwise healthy people.
Predisposing Factors
A.50% to 75% of outbreaks occur in child care settings.
B.Travel to endemic areas.
C.Subjection to unsanitary food handling.
D.Exposure to contaminated water supplies (lakes, rivers, springs, ponds, streams, or wells):
1.Swallowing water from a swimming pool.
E.Hikers and campers.
F.Oral/anal and oral/genital sexual contact.
G.Immunocompromised individuals are at high risk.
Common Complaints
Acute Complaints
A.Explosive, foul-smelling diarrhea.
B.Mucus in stools, bulky stools.
C.Upper abdominal pain or discomfort.
D.Flatulence.
E.Nausea.
F.Anorexia.
G.Weight loss.
Other Signs and Symptoms
Chronic Complaints
A.Intermittent loose stools (but not diarrhea).
B.Steatorrhea.
C.Increased flatulence or distension.
D.Vague abdominal discomfort.
E.Fatigue related to anemia.
F.Profound weight loss (10%–20% of body weight).
G.Malabsorption.
H.Urticaria.
Subjective Data
A.Review onset, duration, and course of symptoms. Is diarrhea acute or chronic?
B.Ask the patient about travel to areas known for giardiasis.
C.Review recreational exposure to water sources, swimming pools, lakes, ponds, rivers, and so on.
D.Review the patient’s intake of medications and other substances that can cause diarrhea, especially antibiotics, laxatives, quinidine, magnesium-containing antacids, excess alcohol, caffeine, herbal teas, digitalis, loop diuretics, antihypertensive agents, and sorbitol-containing (sugar-free) gums and mints.
E.Review the nature of the patient’s bowel movements (BMs), including frequency, consistency, volume, and presence of blood, pus, or mucus.
F.Does diarrhea have any relationship to meals? Onset of diarrhea within hours of ingesting a potentially contaminated food is suggestive of bacterial infection such as Escherischia coli; this is confirmed by checking if others were similarly affected.
G.Ask the patient about associated symptoms that need evaluation, such as fever, abdominal pain, or rash.
H.Ask the patient if other family members or sexual contacts are also ill.
I.Establish the patient’s normal weight, and if any weight has recently been lost, review amount and over what period of time.
Physical Examination
The physical examination may reveal no specific finding.
A.Check temperature, pulse, respirations, blood pressure (BP). Measure height and weight to calculate body mass index (BMI).
B.Inspect: General appearance for signs of dehydration; include evaluation of mucous membranes.
C.Auscultate: Abdomen for bowel sounds in all quadrants.
D.Palpate:
1.Palpate the abdomen for masses, tenderness, guarding, and rebound. Patients with perium-bilical or right lower quadrant (RLQ) pain and copious volumes of watery stool are likely to have a small bowel etiology.
2.Palpate lymph nodes for enlargement.
E.Perform rectal exam.
Diagnostic Tests
A.Routine blood tests, complete blood count (CBC), and electrolytes are usually normal.
B.Stool antigen enzyme-linked immunosorbent assay (ELISA) and direct fluorescence antibody (DFA) are becoming the standard for diagnosis of giardiasis in the United States.
C.Stool culture may be used to rule out other pathogens.
D.Mucus stool for leukocytes: Mucus free of leukocytes is the hallmark of irritable bowel syndrome (IBS); a large number of white cells suggests inflammatory or invasive diarrhea.
E.Stool for ova and parasites; test three times on alternate days. Parasites are passed intermittently, so examine stools on alternating days.
F.Endoscopy to identify cyst in duodenal fluid or small bowel tissue.
Differential Diagnoses
A.Giardiasis.
B.Malabsorption.
C.E. coli infection.
D.IBS.
E.Viral diarrhea.
F.Lactose intolerance.
G.Other bacterial infections, such as Shigella, Salmonella, and Campylobacter.
H.Crohn’s disease (CD).
I.Sprue.
Plan
A.General interventions:
1.Advise adult workers with diarrhea to stay away from day care centers until they become asymptomatic.
2.Advise the patient’s household and sexual contacts to seek medical examination and treatment.
B. 
See Section III: Patient Teaching Guide Diarrhea
:
1.Discuss safe sexual practices.
2.Recommend contact precautions for duration of illness for diapered and/or incontinent children.
3.People with diarrhea caused by giardia should not use recreational water venues, including swimming pools, for 2 weeks after symptoms resolve.
4.Avoidance of alcohol during treatment should be avoided secondary to disulfiram-like effect.
C.Dietary management:
1.Instruct the patient or caregiver to prevent dehydration from diarrhea by increasing fluids.
2.Advise restricting milk products to rule out lactose intolerance. Postgiardia lactose occurs in up to 40% of patients.
3.Instruct backpackers, campers, and people likely to be exposed to contaminated water to avoid drinking directly from streams. To make water safe for drinking, boil the water, or use chemical disinfection or filtration. Boiling water is the most reliable method to make water safe for drinking.
D.Pharmaceutical therapy:
1.Treatment of asymptomatic carriers is not generally recommended.
2.Tinidazole and nitazoxanide are the drugs of choice for treatment:
a.Tinidazole (Tindamax):
i.Adults: 2 g single dose.
ii.Only available in tablet form, it may be crushed by a pharmacist and mixed with flavored syrup.
b.Nitazoxanide (Alinia) has the advantage of treating other intestinal parasites:
i.Age 12 years and older: 500 mg tablet every 12 hours or 25 mL oral suspension every 12 hours with food for 3 days.
3.Metronidazole (Flagyl)—duration of treatment 5 to 7 days:
a.500 mg orally twice a day for 5 to 7 days OR
b.250 mg orally three times a day for 5 to 7 days.
c.For lactating women alternative dosing is a 2-g single dose, with interruption of breasting feeding for 12 to 24 hours.
d.Available in tablets, oral suspension may be prepared by a pharmacist.
4.Albendazole:
a.400 mg daily for 5 days.
b.Available in tablets or suspension.
c.Active against other parasites.
5.Paromomycin (Humatin), a nonabsorbable aminoglycoside, is recommended for treatment of symptomatic infection in pregnant women in the second and third trimesters:
a.Adults: 10 mg/kg orally three times daily for 5 to 10 days.
6.Furazolidone: 100 mg orally four times a day for 7 to 10 days.
7.Quinacrine: 100 mg orally three times a day for 5 days.
Follow-Up
A.Relapses after treatment are common, especially in immunocompromised patients:
1.Persistent symptoms may be attributed to drug resistance, noncompliance with dosing, or immunosuppression
B.If diarrhea persists for 2 weeks or more, secondary evaluation is indicated. Stools should be examined again for blood, leukocytes, and parasites.
C.A repeat course of antimicrobials may be needed for patients with an established diagnosis of giradia.
D.Schedule follow-ups at 6 weeks and 6 months after treatment, as indicated.
E.Giardiasis is a nationally notifiable disease. Cases should be reported to the local or state health departments.
Consultation/Referral
A.Consult a physician if the patient has no relief of symptoms after completion of therapies.
Individual Considerations
A.Pregnancy:
1.Treatment of patients during pregnancy is recommended. Giardiasis in pregnancy is associated with dehydration, malabsorption, or severe symptoms.
2.Malabsorptive symptoms may persist because regeneration of functioning intestinal mucosa requires time.
B.Geriatrics:
1.Anemia, weight loss, and anorexia have been the most prominent signs in the elderly.