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Giardiasis: Epidemiology, clinical manifestations, and diagnosis

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


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 "Giardiasis: Treatment and prevention".)


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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Literature review current through: Nov 2017. | This topic last updated: Sep 27, 2016.
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  1. Feng Y, Xiao L. Zoonotic potential and molecular epidemiology of Giardia species and giardiasis. Clin Microbiol Rev 2011; 24:110.
  2. Roberts DM, Craft JC, Mather FJ, et al. Prevalence of giardiasis in patients with cystic fibrosis. J Pediatr 1988; 112:555.
  3. Muhsen K, Levine MM. A systematic review and meta-analysis of the association between Giardia lamblia and endemic pediatric diarrhea in developing countries. Clin Infect Dis 2012; 55 Suppl 4:S271.
  4. Harvey K, Esposito DH, Han P, et al. Surveillance for travel-related disease--GeoSentinel Surveillance System, United States, 1997-2011. MMWR Surveill Summ 2013; 62:1.
  5. Boggild AK, Geduld J, Libman M, et al. Travel-acquired infections and illnesses in Canadians: surveillance report from CanTravNet surveillance data, 2009-2011. Open Med 2014; 8:e20.
  6. Schlagenhauf P, Weld L, Goorhuis A, et al. Travel-associated infection presenting in Europe (2008-12): an analysis of EuroTravNet longitudinal, surveillance data, and evaluation of the effect of the pre-travel consultation. Lancet Infect Dis 2015; 15:55.
  7. Giardiasis Surveillance — United States, 2011–2012. http://www.cdc.gov/mmwr/preview/mmwrhtml/ss6403a2.htm?s_cid=ss6403a2_e#Tab1 (Accessed on April 30, 2015).
  8. Caeiro JP, Mathewson JJ, Smith MA, et al. Etiology of outpatient pediatric nondysenteric diarrhea: a multicenter study in the United States. Pediatr Infect Dis J 1999; 18:94.
  9. Greig JD, Michel P, Wilson JB, et al. A descriptive analysis of giardiasis cases reported in Ontario, 1990-1998. Can J Public Health 2001; 92:361.
  10. Sagebiel D, Weitzel T, Stark K, Leitmeyer K. Giardiasis in kindergartens: prevalence study in Berlin, Germany, 2006. Parasitol Res 2009; 105:681.
  11. Hill DR, Nash TE. Intestinal flagellate and ciliate infections. In: Tropical Infectious Diseases: Principles, Pathogens and Practice, 3rd ed, Guerrant RL, Walker DA, Weller PF (Eds), Saunders Elsevier, Philadelphia 2011. p.623.
  12. Dykes AC, Juranek DD, Lorenz RA, et al. Municipal waterborne giardiasis: an epidemilogic investigation. Beavers implicated as a possible reservoir. Ann Intern Med 1980; 92:165.
  13. Mintz ED, Hudson-Wragg M, Mshar P, et al. Foodborne giardiasis in a corporate office setting. J Infect Dis 1993; 167:250.
  14. Quick R, Paugh K, Addiss D, et al. Restaurant-associated outbreak of giardiasis. J Infect Dis 1992; 166:673.
  15. Overturf GD. Endemic giardiasis in the United States--role of the daycare center. Clin Infect Dis 1994; 18:764.
  16. Moldwin RM. Sexually transmitted protozoal infections. Trichomonas vaginalis, Entamoeba histolytica, and Giardia lamblia. Urol Clin North Am 1992; 19:93.
  17. Escobedo AA, Almirall P, Alfonso M, et al. Sexual transmission of giardiasis: a neglected route of spread? Acta Trop 2014; 132:106.
  18. Bouzid M, Halai K, Jeffreys D, Hunter PR. The prevalence of Giardia infection in dogs and cats, a systematic review and meta-analysis of prevalence studies from stool samples. Vet Parasitol 2015; 207:181.
  19. RENDTORFF RC. The experimental transmission of human intestinal protozoan parasites. II. Giardia lamblia cysts given in capsules. Am J Hyg 1954; 59:209.
  20. Nash TE. Unraveling how Giardia infections cause disease. J Clin Invest 2013; 123:2346.
  21. Franzén O, Jerlström-Hultqvist J, Castro E, et al. Draft genome sequencing of giardia intestinalis assemblage B isolate GS: is human giardiasis caused by two different species? PLoS Pathog 2009; 5:e1000560.
  22. Sahagún J, Clavel A, Goñi P, et al. Correlation between the presence of symptoms and the Giardia duodenalis genotype. Eur J Clin Microbiol Infect Dis 2008; 27:81.
  23. Gilman RH, Brown KH, Visvesvara GS, et al. Epidemiology and serology of Giardia lamblia in a developing country: Bangladesh. Trans R Soc Trop Med Hyg 1985; 79:469.
  24. Istre GR, Dunlop TS, Gaspard GB, Hopkins RS. Waterborne giardiasis at a mountain resort: evidence for acquired immunity. Am J Public Health 1984; 74:602.
  25. Oksenhendler E, Gérard L, Fieschi C, et al. Infections in 252 patients with common variable immunodeficiency. Clin Infect Dis 2008; 46:1547.
  26. Smith PD, Lane HC, Gill VJ, et al. Intestinal infections in patients with the acquired immunodeficiency syndrome (AIDS). Etiology and response to therapy. Ann Intern Med 1988; 108:328.
  27. Stark D, Barratt JL, van Hal S, et al. Clinical significance of enteric protozoa in the immunosuppressed human population. Clin Microbiol Rev 2009; 22:634.
  28. Nash TE, Ohl CA, Thomas E, et al. Treatment of patients with refractory giardiasis. Clin Infect Dis 2001; 33:22.
  29. Nash TE, Herrington DA, Losonsky GA, Levine MM. Experimental human infections with Giardia lamblia. J Infect Dis 1987; 156:974.
  30. Pickering LK, Woodward WE, DuPont HL, Sullivan P. Occurrence of Giardia lamblia in children in day care centers. J Pediatr 1984; 104:522.
  31. López CE, Dykes AC, Juranek DD, et al. Waterborne giardiasis: a communitywide outbreak of disease and a high rate of asymptomatic infection. Am J Epidemiol 1980; 112:495.
  32. Donowitz JR, Alam M, Kabir M, et al. A Prospective Longitudinal Cohort to Investigate the Effects of Early Life Giardiasis on Growth and All Cause Diarrhea. Clin Infect Dis 2016; 63:792.
  33. Kotloff KL, Nataro JP, Blackwelder WC, et al. Burden and aetiology of diarrhoeal disease in infants and young children in developing countries (the Global Enteric Multicenter Study, GEMS): a prospective, case-control study. Lancet 2013; 382:209.
  34. Cantey PT, Roy S, Lee B, et al. Study of nonoutbreak giardiasis: novel findings and implications for research. Am J Med 2011; 124:1175.e1.
  35. Singh KD, Bhasin DK, Rana SV, et al. Effect of Giardia lamblia on duodenal disaccharidase levels in humans. Trop Gastroenterol 2000; 21:174.
  36. Rana SV, Bhasin DK, Vinayak VK. Lactose hydrogen breath test in Giardia lamblia-positive patients. Dig Dis Sci 2005; 50:259.
  37. Vega-Franco L, Meza C, Romero JL, et al. Breath hydrogen test in children with giardiasis. J Pediatr Gastroenterol Nutr 1987; 6:365.
  38. Lengerich EJ, Addiss DG, Juranek DD. Severe giardiasis in the United States. Clin Infect Dis 1994; 18:760.
  39. Gunasekaran TS, Hassall E. Giardiasis mimicking inflammatory bowel disease. J Pediatr 1992; 120:424.
  40. Mørch K, Hanevik K, Robertson LJ, et al. Treatment-ladder and genetic characterisation of parasites in refractory giardiasis after an outbreak in Norway. J Infect 2008; 56:268.
  41. Botero-Garcés JH, García-Montoya GM, Grisales-Patiño D, et al. Giardia intestinalis and nutritional status in children participating in the complementary nutrition program, Antioquia, Colombia, May to October 2006. Rev Inst Med Trop Sao Paulo 2009; 51:155.
  42. Prado MS, Cairncross S, Strina A, et al. Asymptomatic giardiasis and growth in young children; a longitudinal study in Salvador, Brazil. Parasitology 2005; 131:51.
  43. Halliez MC, Buret AG. Extra-intestinal and long term consequences of Giardia duodenalis infections. World J Gastroenterol 2013; 19:8974.
  44. Hanevik K, Wensaas KA, Rortveit G, et al. Irritable bowel syndrome and chronic fatigue 6 years after giardia infection: a controlled prospective cohort study. Clin Infect Dis 2014; 59:1394.
  45. Heyworth MF. Diagnostic testing for Giardia infections. Trans R Soc Trop Med Hyg 2014; 108:123.
  46. Garcia LS, Shimizu RY. Evaluation of nine immunoassay kits (enzyme immunoassay and direct fluorescence) for detection of Giardia lamblia and Cryptosporidium parvum in human fecal specimens. J Clin Microbiol 1997; 35:1526.
  47. Al FD, Kuştimur S, Ozekinci T, et al. The use of enzyme linked immunosorbent assay (ELISA) and direct fluorescent antibody (DFA) methods for diagnosis of Giardia intestinalis. Turkiye Parazitol Derg 2006; 30:275.
  48. Rosoff JD, Sanders CA, Sonnad SS, et al. Stool diagnosis of giardiasis using a commercially available enzyme immunoassay to detect Giardia-specific antigen 65 (GSA 65). J Clin Microbiol 1989; 27:1997.
  49. Weitzel T, Dittrich S, Möhl I, et al. Evaluation of seven commercial antigen detection tests for Giardia and Cryptosporidium in stool samples. Clin Microbiol Infect 2006; 12:656.
  50. Jahan N, Khatoon R, Ahmad S. A Comparison of Microscopy and Enzyme Linked Immunosorbent Assay for Diagnosis of Giardia lamblia in Human Faecal Specimens. J Clin Diagn Res 2014; 8:DC04.
  51. Aziz H, Beck CE, Lux MF, Hudson MJ. A comparison study of different methods used in the detection of Giardia lamblia. Clin Lab Sci 2001; 14:150.
  52. Vasoo S, Pritt BS. Molecular diagnostics and parasitic disease. Clin Lab Med 2013; 33:461.
  53. Boadi S, Polley SD, Kilburn S, et al. A critical assessment of two real-time PCR assays targeting the (SSU) rRNA and gdh genes for the molecular identification of Giardia intestinalis in a clinical laboratory. J Clin Pathol 2014; 67:811.
  54. Buss SN, Leber A, Chapin K, et al. Multicenter evaluation of the BioFire FilmArray gastrointestinal panel for etiologic diagnosis of infectious gastroenteritis. J Clin Microbiol 2015; 53:915.
  55. Mengelle C, Mansuy JM, Prere MF, et al. Simultaneous detection of gastrointestinal pathogens with a multiplex Luminex-based molecular assay in stool samples from diarrhoeic patients. Clin Microbiol Infect 2013; 19:E458.
  56. Claas EC, Burnham CA, Mazzulli T, et al. Performance of the xTAG® gastrointestinal pathogen panel, a multiplex molecular assay for simultaneous detection of bacterial, viral, and parasitic causes of infectious gastroenteritis. J Microbiol Biotechnol 2013; 23:1041.
  57. van den Bijllaardt W, Overdevest IT, Buiting AG, Verweij JJ. Rapid clearance of Giardia lamblia DNA from the gut after successful treatment. Clin Microbiol Infect 2014; 20:O972.
  58. Dreelin EA, Ives RL, Molloy S, Rose JB. Cryptosporidium and Giardia in surface water: a case study from Michigan, USA to inform management of rural water systems. Int J Environ Res Public Health 2014; 11:10480.
  59. Hiatt RA, Markell EK, Ng E. How many stool examinations are necessary to detect pathogenic intestinal protozoa? Am J Trop Med Hyg 1995; 53:36.
  60. Goka AK, Rolston DD, Mathan VI, Farthing MJ. The relative merits of faecal and duodenal juice microscopy in the diagnosis of giardiasis. Trans R Soc Trop Med Hyg 1990; 84:66.