(Giardiasis)

Symptomatic infection causes a broad spectrum of clinical manifestations.Acute watery diarrhea with abdominal pain may develop in patients with clinical illness, or they may experience a protracted, intermittent, often debilitating disease, which is characterized by passage of foul-smelling stools associated with flatulence, abdominal distention, and anorexia. Anorexia combined with malabsorption can lead to significant weight loss, failure to thrive, and anemia. Asymptomatic infection is common.


Giardia lamblia is a flagellate protozoan that exists in trophozoite and cyst forms; the infective form is the cyst.Infection is limited to the small intestine and biliary tract.


Giardiasis has a worldwide distribution. Humans are the principal reservior of infection, but Giardia organisms can infect dogs, cats, beavers, and other animals. These animals can contaminate water with feces containing cysts that are infectious for humans. Persons become infected directly (by hand-to-mouth transfer of cysts from feces of an infected person) or indirectly (by ingestion of fecally contaminated water or food). Many persons who become infected with G lamblia remain asymptomatic.Most community-wide epidemics result from a contaminated water suply. Epidemics resulting from porson-to-person transmission occur in child care centers and in institutions for mentally retarded persons . Staff and family members in contact with persons in these settings occasionally become infected. Humoral immunodeficiencies predispose to chronic symptomatic G lamblia infections. Surveys conducted in the United States have demonstrated prevalence rates of Giarbia organisms in stool specimens that range from 1% to 20%, depending on geographic location and age. Duration of cyst excretion is variable and may be months. The disease is communicable for as long as the infected person excretes cysts.
The incubation period usually is 1 to 4 weeks.



Identification of trophozoites or cysts on direct smear examination or immunofluorescent antibody(IFA) testing of stool specimens or duodenal fluid or detection of G lamblia antigens in these specimens by enzyme immunoassay (EIA) is diagnostic. Commercially available EIA techniques for stool specimens have greater sensitivity than microscopy but fail to detect other parasites. One commercially available IFA test allows microscopic detection of Giardia and Cryptosporidium species in stool with a sensitivity of approximately 75% . A single direct smear examination of stool has a sensitivity of 50% to 75% , which is increased to approximately 95% by testing 3 specimens. To enhance detection, microscopic examination of stool specimens or duodenal fluid should be performed soon after they are obtained , or stool should be mixed, placed in fixative, concentrated, and examined by wet mount and permanent stain. Commercially available stool collection kits containing a vial of 10% formalin and a vial of polyvinyl alcohol fixative in chilproof of containers are convenient for preserving stool specimens collected at home . Laboratories can reduce  reagent and personnel costs by pooling specimens before evaluation by microscopy or EIA. Examination of duodenal contents obtained by direct aspiration or by using a commercially available string test (Entero-Test,HDC Corporation, San Jose , Calif) is a more sensitive procedure than examination of a single stool specimen. Rarely, duodenal biopsy is required for diagnosis.


Metronidazole is the drug of choice; a 5- to 7-day course of therapy has a cure rate of 80% to 95%. Tinidazole, a nitroimidazole , has a cure rate of 90% to 100% after a single dose, but limited safety and efficacy data are available in children. Furazolidone is 72% to 100% effective when given for 7 to 10 days and has an acceptable flavor for pediatric use . Albendazole has been shown to be as effective as metronidazole for treating giardiasis in children, and it has fewer adverse effects. Albendazole can be formulated into a suspension and has been given to children 2 years of age or older at a dose of 400 mg by mouth daily for 5 days.paromomycin, a nonabsorbable aminoglycoside that is 50% to 70% effective, is recommended for treatment of symptomatic infection in pregnant women. Quinacrine can be obtained by special order (see Drugs for Parasitic Infections , p 693).
If therapy fails, a course can be repeated with the same drug. Relapse is common in immunocompromised patients who may require prolonged treatment.
Some experts recommend combination therapy for giardiasis in immunocompromised patients who are unreponsive to courses of both drugs used separately.
Treatment of asymptomatic carriers generally is not recommended.Possible exceptions to prevent transmission are in households of patients with hypogamma globulinemia or cystic fibrosis and in pregnant women with toddlers.


In addition to standard precautions, contact precautions for the duration of illness are recommended for diapered and incontinent children.


In child care centers, improved sanitation and personal hygiene should be emphasized (see also Children in Out-of-Home Child Care, p 105). Hand washing by staff and children should be emphasized, especially after toilet use or handling of soiled diapers. When an outbreak is suspected, the local health department should be contacted, and an epidemiologic investigation should be undertaken to identify and treat all symptomatic children, child care workers, and family members infected with G lamblia, Persons with diarrhea should be excluded from the child care center until they become asymptomatic.Treatment of asymptomatic carriers is not effective for outbreak control. Exclusion of carriers from child care is not recommended.
Waterborne outbreaks can be prevented by the combination of adequate filtration of water from surface water sources (eg, lakes, rivers, streams), chlorination , and maintenance of water distribution systems.
Backpackers, campers , and persons likely to be exposed to contaminated water should avoid drinking directly from streams. Boiling of water will kill the infective cysts and other waterborne pathogens.


Red Book 2000