Giardiasis is a parasitic disease of the upper small intestine caused by the non-invasive protozoan Giardia duodenalis (synonyms G. lamblia and G. intestinalis) [1][3][2]. The parasite has a two-stage life cycle comprising an infectious cyst form and a trophozoite form that colonizes the small intestine, with cysts excreted in feces serving as the transmissible stage [2].
Disease overview
ParasiticGiardiasis
贾第虫病
Evidence-backed informationEN 5/7 applicable sections · ZH 5/7 applicable sectionsUpdated Sep 3, 2026
Giardiasis is a parasitic diarrheal illness caused by Giardia duodenalis (also known as G. lamblia or G. intestinalis) and represents a leading cause of waterborne and foodborne diarrhea, daycare-associated outbreaks, and traveler's diarrhea worldwide [1][2]. The infection is especially common in children and travelers, with an estimated 280 million people affected annually, and asymptomatic infections are equally common [3][2]. Clinical presentation ranges from asymptomatic carriage to acute or chronic diarrhea with malabsorption, and treatment-refractory disease is increasingly reported, making giardiasis a persistent global public-health concern [1][4][3].
Read the full clinical and epidemiological profile6
Clinical manifestations range from asymptomatic infection to severe diarrhea; approximately 50–75% of infected children are asymptomatic, while symptomatic cases may present with acute or chronic diarrhea, including steatorrhea characterized by greasy, foul-smelling, floating stools [1][2]. Accompanying features include abdominal pain, weight loss, bloating, weakness from dehydration and malabsorption, and less commonly skin rash, hives, and joint swelling [2]. Symptoms typically develop 1–3 weeks after exposure and, without treatment, may last two to six weeks or longer, with some infections progressing to chronic disease or post-infectious sequelae such as irritable bowel syndrome and food allergies [3][2].
Giardiasis is a globally distributed cause of diarrhea and intestinal enteropathy [4]. The disease is a recognized cause of waterborne and foodborne diarrhea, daycare-center outbreaks, and traveler's diarrhea [1]. Treatment-refractory giardiasis appears to be increasing, with reports that 5-nitroimidazole-refractory infection may occur in up to 50% of cases in some clinical series, underscoring the evolving therapeutic challenge [4].
Transmission occurs via the fecal-oral route when Giardia cysts excreted in feces contaminate food, drinking water, or recreational water that is subsequently ingested [1][2]. Person-to-person spread is well documented, and zoonotic transmission can also occur, particularly through contact with infected pets [1][2]. Cysts are environmentally resilient and may remain viable in cold water for nearly three months, and ingestion of only a small number of cysts is sufficient to establish infection in a new host [2].
Prevention centers on interrupting the fecal-oral route through proper personal hygiene, safe handling and thorough cooking of food, and adequate sanitation or treatment of drinking and recreational water [1][2]. In high-risk settings such as daycare centers and during travel to endemic regions, attention to hand hygiene, avoidance of untreated water, and care with food preparation are particularly important to reduce transmission [1][2].
- 1Leung AKC et al. Giardiasis: An Overview. Recent Pat Inflamm Allergy Drug Discov. 2019. PMID: 31210116. doi: 10.2174/1872213X13666190618124901.PubMed: https://pubmed.ncbi.nlm.nih.gov/31210116/
- 2Wikipedia contributors. Giardiasis - Wikipedia [Internet]. Wikipedia. cited 2 Sept 2026.Available from: https://en.wikipedia.org/wiki/Giardiasis
- 3Einarsson E et al. An up-date on Giardia and giardiasis. Curr Opin Microbiol. 2016 Dec. PMID: 27501461. doi: 10.1016/j.mib.2016.07.019.PubMed: https://pubmed.ncbi.nlm.nih.gov/27501461/
- 4Mørch K et al. Giardiasis treatment: an update with a focus on refractory disease. Curr Opin Infect Dis. 2020 Oct. PMID: 32773501. doi: 10.1097/QCO.0000000000000668.PubMed: https://pubmed.ncbi.nlm.nih.gov/32773501/
- 5McFarland LV et al. Systematic review and meta-analysis of Saccharomyces boulardii in adult patients. World J Gastroenterol. 2010 May 14. PMID: 20458757. doi: 10.3748/wjg.v16.i18.2202.PubMed: https://pubmed.ncbi.nlm.nih.gov/20458757/
Coverage
Reporting countries and regions
Trends by reporting country
Monthly patterns over time
Research Radar
Recent related research
A Mathematical Model for the Transmission of Giardiasis Incorporating Resistance Strain and Second Line of Treatment
International Journal of Development Mathematics (IJDM)
Literature links are provided for discovery and do not alter or validate the surveillance series above.
Data access
Page dataset index with source links and update metadata.
Official sourcesAuthority, cadence, notes36
ECDC Surveillance Atlas — Belgium Annual Baseline
Belgium
Belgium annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Bulgaria Annual Baseline
Bulgaria
Bulgaria annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
Canada PHAC CNDSS Annual
Canada
Canada is the national jurisdiction; subdivision feeds are registered separately.
Public Health Ontario IDTO Monthly
Ontario, Canada
Ontario-level current-year preliminary monthly case counts from Public Health Ontario's IDTO report.
ECDC Surveillance Atlas — Cyprus Annual Baseline
Cyprus
Cyprus annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Czechia Annual Baseline
Czechia
Czechia annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
Germany RKI SurvStat 2.0
Germany
RKI SurvStat national weekly notification export; raw ZIP exports are retained and recent weeks are overwritten for revisions.
ECDC Surveillance Atlas — Estonia Annual Baseline
Estonia
Estonia annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Spain Annual Baseline
Spain
Spain annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
Finland THL Infectious Diseases Register
Finland
Finland THL Infectious Diseases Register national monthly case counts. The current month is ingested as provisional and the latest three months are refreshed for source revisions.
ECDC Surveillance Atlas — United Kingdom Annual Baseline
United Kingdom
United Kingdom annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Greece Annual Baseline
Greece
Greece annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Croatia Annual Baseline
Croatia
Croatia annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Hungary Annual Baseline
Hungary
Hungary annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
Ireland HPSC Notifiable Diseases Hub
Ireland
Ireland HPSC national weekly notifiable-disease totals from the official ArcGIS FeatureServer. Internal ingestion is enabled; public release remains disabled pending written redistribution permission.
Iceland Directorate of Health Annual Dashboard
Iceland
National annual case notifications by disease. Published values can be revised retrospectively and remain annual period totals.
Iceland Directorate of Health STI Dashboard
Iceland
Monthly STI diagnosis facts from laboratory and registry surveillance; the official dashboard is published on a quarterly schedule.
Iceland Directorate of Health Respiratory Dashboard
Iceland
ISO-week respiratory diagnosis counts. Hospitalizations, samples, and vaccination indicators are separate measures and are not counted as diagnoses.
Iceland Directorate of Health Historical Registry
Iceland
Historical official registry tables for 1997–2021, with annual totals and disease-specific monthly notification facts retained at source grain.
Iceland Directorate of Health Legacy ICD Monthly
Iceland
Historical Saga EHR ICD encounter counts for 1997–2020. This clinical measure is non-comparable with registry notifications and is kept separate.
ECDC Surveillance Atlas — Italy Annual Baseline
Italy
Italy annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
JP NIID Weekly
Japan
Japan weekly infectious disease surveillance via NIID/JIHS.
ECDC Surveillance Atlas — Lithuania Annual Baseline
Lithuania
Lithuania annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Luxembourg Annual Baseline
Luxembourg
Luxembourg annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Latvia Annual Baseline
Latvia
Latvia annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Malta Annual Baseline
Malta
Malta annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
Norway FHI MSIS Statistics Bank
Norway
Norway FHI MSIS national monthly notifications from the official Allvis frontend API; adapter contract checks guard the unversioned endpoint.
New Zealand PHF Science Monthly Notifiable Diseases
New Zealand
PHF Science (formerly ESR) monthly notifiable disease surveillance data via internal globalID2 crawler
ECDC Surveillance Atlas — Poland Annual Baseline
Poland
Poland annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Portugal Annual Baseline
Portugal
Portugal annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Romania Annual Baseline
Romania
Romania annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
Sweden Public Health Agency SmiNet
Sweden
Sweden SmiNet national monthly reported cases from the official Public Health Agency statistics pages; public release is enabled with closed-month publication and revisable recent-month refreshes.
ECDC Surveillance Atlas — Slovenia Annual Baseline
Slovenia
Slovenia annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
ECDC Surveillance Atlas — Slovakia Annual Baseline
Slovakia
Slovakia annual Member-State reported case counts from the ECDC Surveillance Atlas. Missing topic/year cells remain unknown and published zeroes are preserved. Data provided by ECDC based on data reported by EU/EEA Member States.
US CDC NNDSS
United States
CDC National Notifiable Diseases Surveillance System provisional data.
US CDC NHSS HIV
United States
CDC NNDSS weekly data plus NHSS annual national HIV diagnoses