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Epidemiology, clinical manifestations, and diagnosis of giardiasis

Authors
Karin Leder, MBBS, FRACP, PhD, MPH, DTMH
Peter F Weller, MD, FACP
Section Editor
Edward T Ryan, MD, DTMH
Deputy Editor
Elinor L Baron, MD, DTMH

INTRODUCTION

Giardia duodenalis (also known as G. lamblia or G. intestinalis) is a protozoan parasite capable of causing sporadic or epidemic diarrheal illness. Giardiasis is an important cause of waterborne and foodborne disease, daycare center outbreaks, and illness in international travelers.

The epidemiology, microbiology, pathogenesis, clinical manifestations, and diagnosis of giardiasis will be reviewed here. The treatment and prevention of giardiasis are discussed separately. (See "Treatment and prevention of giardiasis".)

EPIDEMIOLOGY

G. duodenalis infection occurs worldwide [1]. High-risk groups include infants, young children, international adoptees, travelers, immunocompromised individuals, and patients with cystic fibrosis [2].

Giardiasis is especially common in areas with poor sanitary conditions and limited water-treatment facilities. In resource-limited settings, the prevalence of giardiasis has been reported to be as high as 20 to 40 percent [1]. The highest rates of infection in resource-limited areas occur among children <5 years. Many individuals with G. duodenalis identified in stool samples are asymptomatic, a point highlighted by studies that identified Giardia more commonly in the stool of asymptomatic individuals than among individuals with acute diarrhea [3].

Giardiasis is a well-recognized cause of enteric disease among international travelers in the United States, Canada, and Europe [4-6]. In the United States in 2012, a total of 15,223 cases were reported [7]. In a study including 147 pediatric patients with acute nondysenteric diarrhea in the United States, giardiasis was the cause in 15 percent of cases, second only to rotavirus [8]. One report in Canada noted an adjusted incidence rate of 25.8 cases per 100,000 population between 1990 and 1998 [9]. Almost 40 percent of cases occurred in travelers; other important sources of infection included unfiltered water and person-to-person transmission. A German study noted a prevalence of giardiasis of 11.5 cases per 100,000 population among one- to five-year-olds [10].

                 

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