Giardiasis and the Risks of Visiting Grandma

Abstract and Commentary

By Philip R. Fischer, MD, DTM&H, and Jane R. Rosenman, MD

Dr. Fischer is Professor of Pediatrics, Division of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN, and Dr. Rosenman is Instructor, Division of General Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN.

Dr. Fischer and Dr. Rosenman report no consultants, stockholders, speaker’s bureaus, research, or other financial relationships with companies having ties to this field of study.

Synopsis: Characteristics of international travel, immigration, and adoption help to shape the epidemiology of giardiasis. The risks to travelers who are visiting friends and relatives in developing countries are significant, and may be decreased with a stronger emphasis on pre-travel counseling.

Source: Ekdahl K, et al. Imported Giardiasis: Impact of International Travel, Immigration, and Adoption. Am J Trop Med Hyg. 2005;72:825-830.

Giardiasis, caused by the waterborne protozoan parasite Giardia lamblia, also known as G. intestinalis, and G. duodenalis, is a common cause of diarrhea worldwide. The highest incidence of disease is seen in developing countries. As overseas travel becomes more accessible, and as international adoption continues to rise, the epidemiology of giardiasis in developed countries is changing.

Ekdahl and colleagues describe the impact of immigration and international travel on the epidemiology of giardiasis in Sweden from 1997 to 2003. In addition, the relative risk estimates of giardiasis are discussed in detail.

Although this study looked at individuals arriving or returning to Sweden between 1997 and 2003, Ekdahl et al assert that the denominator based data from this study can likely be generalized to other Western populations. A total of 11,590 subjects comprised 5 main groups with giardiasis: travel-related (3697; 32%), newly-arrived immigrants (4151; 36%), internationally adopted children (455; 4%), domestic cases (1708; 15%), and a fifth group for which there was not sufficient information to be studied (1441; 13%). The travel-related group included returning travelers having visited friends and relatives (VFRs); these were generally individuals with family roots within the country that was the source of infection.

Risks were evaluated for each of the groups. For returning travelers, the overall risk of having acquired giardiasis was 5.3 per 100,000. The highest unadjusted risks were seen in travelers to the Indian Subcontinent, East Africa, West Africa, South America, and Central America. Twenty-four percent of cases of giardiasis were seen in VFRs. The highest age-related risk of Giardia infection was in young children. There was a 10- to 20-fold higher risk in refugees and other immigrants than in returning travelers (prevalence of 1000 to 2000 per 100,000). Of all internationally adopted children under 10 years of age arriving to Sweden during this period, 8% had giardiasis. Giardia prevalence was 10,000-50,000 per 100,000 children for more than half of the countries from which the children came.

Ekdahl et al acknowledge that some bias may exist in the travel risk calculations. Travelers returning from tropical countries are more likely to seek medical evaluation for gastrointestinal complaints, and medical practitioners are more likely to investigate travelers returning from endemic countries. Due to the sometime insidious nature of giardiasis, it may be difficult to determine the specific onset of infection.

While the risk for giardiasis in immigrants/refugees was much higher than in tourists, there was an even higher risk among internationally adopted children. A contributing factor may be that returning travelers generally are evaluated only if gastrointestinal symptoms are present, whereas most internationally adopted children, symptomatic or not, are routinely screened for giardiasis.


Giardia infection can occur by person-to-person contact (via fecal-oral route) but, most commonly, by ingestion of contaminated drinking water, or possibly food. Estimated asymptomatic carriage rates in the United States are 3-20%, depending on the region. In studies of children under 36 months in daycare centers, the prevalence of Giardia cysts was 21-26% in one study.1 In Santa Clara County, CA, between October 2001 and January 2004, immigrants and refugees presenting to a refugee clinic were screened for parasitic infections. Giardia lamblia was the most common protozoan isolated, and was more likely among children than adults.2

Asymptomatic carriage, though generally well tolerated, can serve as a reservoir of infection for contacts of returned travelers. Most common clinical manifestations include diarrhea, abdominal cramping, and bloating. A more prolonged, incapacitating disease may occur in those at higher risk, including children, employees in childcare centers, men who have sex with men, travelers to endemic areas, and certain immunodeficient hosts. Failure to thrive and anemia may occur in protracted giardiasis, which may have a lasting impact on the physical and cognitive development of children. In addition to the clinical impact of giardiasis, the financial costs may also be quite significant.3,4

During recent decades, a large number of refugees and immigrants have been arriving in Western countries from regions outside the normal tourist routes. Many of these individuals are now returning to visit their countries of origin and taking their families along with them. These travelers visiting friends and relatives, so-called VFRs, are at high risk for travel-related illness, including giardiasis. In the United States, 20% of the population are first-degree immigrants, or their children are. In 2002, 40% of United States international air travelers were VFRs. This group of travelers is less likely to seek pre-travel consultation, more likely to travel to remote areas, and usually stays longer than other tourist travelers. Since children, in general, are at highest risk of acquiring giardiasis. These children, in particular, are at especially high risk and should be monitored closely for gastrointestinal complaints upon returning.5

Recommended stool studies for symptomatic individuals are stool enzyme immunoassay (EIA), with 87-100% sensitivity and 100% specificity, or serum immunofluorescence antibody (IFA) determinations, with 100% sensitivity and specificity.6,7 In addition, stool specimens may be evaluated for ova and parasites by microscopy; one stool sample has a 75-95% sensitivity, and 3 samples collected on different days increase the sensitivity to about 95%. Microscopy in returning travelers is also helpful to identify other concomitant parasitic infections. While asymptomatic carriers do not technically require specific treatment, curative therapy can reduce the risk of transmission. It is, therefore, especially useful for infected children who are contacts of immunocompromised and pregnant individuals.2,6

If symptomatic giardiasis does occur, treatment includes rehydration and correction of electrolyte abnormalities. In addition, a 5-7-day course of metronidazole, 250 mg 3 times a day for adults and 15 mg/kg/day divided in 3 daily doses for children, remains the antiparasitic treatment of choice, with cure rates of 80-95%. Furazolidone, 100 mg5 4 times a day for adults or 6 mg/kg/day divided in 4 daily doses for children, is 70-100% effective when taken for 7-10 days, and is available in a liquid form for children. Due to the risk of mild hemolysis, furazolidone should be avoided in infants under one month old and individuals with known G6PD deficiency. Albendazole is as effective as metronidazole in treating giardiasis and is useful against coexisting helminth infections. Tinidazole has a cure rate of 90-100% when taken as a single dose, but is not currently available in the United States.6,8,9 Recent evidence suggests that nitazoxanide, a nitrothiazolylsalicylamide derivative, is as effective as metronidazole for giardiasis and may be better tolerated. The recommended dose is 100 mg for children 12-47 months of age, 200 mg for 4-11 year olds, and 500 mg for older children and adults.10 Related to concerns about teratogenicity of metronidazole during the first trimester, paromomycin may be used in pregnant women, and is 50-70% effective.6,8

Traveler’s diarrhea is the most common travel-related illness.5 Giardiasis is a known cause of diarrhea in returned travelers, and it is also seen among internationally adopted children and new immigrants. Former immigrants or refugees returning to their native countries, often with their children to visit friends and relatives, deserve special attention both pre- and post-travel. Children in this group of travelers are at even higher risk for serious consequences, many of which could be avoided with appropriate counseling and the implementation of food and water precautions.


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