Giardiasis

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Last reviewed: 15 Jan 2026

Last updated: 03 Jan 2025

Giardiasis symptoms vary from asymptomatic passage of cysts to acute self-limiting diarrhea or chronic diarrhea. It is associated with growth restriction in children.

Diagnosis is by detection of cysts or trophozoites in a stool sample or by molecular-based detection of antigens or parasite-specific nucleic acids.

Microscopy with direct fluorescent antibody testing is the gold standard for diagnosing giardiasis.

Tinidazole, metronidazole, or nitazoxanide is recommended as first-line treatment.

Transmission is via the fecal-oral route. Personal hygiene is key to prevention.

Definition

Giardiasis is an enteric infection caused by a eukaryotic, flagellated, binucleated protozoan parasite called Giardia duodenalis (formerly known as Giardia lamblia or Giardia intestinalis).[1] First described in 1681, it is a major cause of diarrheal disease in human beings and other mammals.[2][3] Children and immunocompromised people may present with weight loss and faltering growth, or other developmental impairments, due to gut dysfunction and nutritional deficiencies.[4]

History and exam

Key diagnostic factors

diarrhea
frequent belching

Full details

Other diagnostic factors

abdominal bloating and discomfort
malaise
weight loss
nausea and vomiting

Full details

Risk factors

contaminated water/food
domestic animals living in or around the house
hypogammaglobulinemia
young age
male sex
day-care center attendance
oral-anal sexual contact
recent antibiotic use

Full details

Diagnostic tests

1st tests to order

direct fluorescence antibody (DFA) test
enzyme-linked immunosorbent assay
nucleic acid amplification test, polymerase chain reaction of stool sample
stool microscopy
CBC

Full details

Tests to consider

Lateral flow immunoassay (e.g., ImmunoCard STAT!)
duodenal aspirates and biopsies
string test (EnteroTest)

Full details

Treatment algorithm

ACUTE

nonpregnant adult or child

pregnant; first trimester

pregnant; second or third trimester

ONGOING

treatment failure or resistance

Contributors

Authors

Luther A. Bartelt, MD

Assistant Professor of Medicine

University of North Carolina School of Medicine

Division of Infectious Diseases

Chapel Hill

Disclosures

LAB is reimbursed by UpToDate for authorship. LAB has received funding from the National Institutes of Health. LAB is the author of two articles cited in this topic.

Acknowledgements

Dr Luther Bartelt would like to gratefully acknowledge Dr Fida Khan and Dr Musaddiq Waheed, previous contributors to this topic.

Disclosures

FK and MW declared that they had no competing interests.

Peer reviewers

Zana Nikolla, MD

Faculty of Medicine

University of Tirana

Tirana

Albania

Disclosures

ZN declares that she has no competing interests.

Rodney Adam, MD

Professor of Medicine and Immunobiology

University of Arizona

Tucson

Declarações

RA declares that he has no competing interests.

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Referências

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Principais artigos

Center for Disease Control and Prevention. CDC Yellow Book 2024: health information for international travel. Section 5: travel-associated infections & diseases - giardiasis. May 2023 [internet publication].Texto completo

Centers for Disease Control and Prevention. Giardia: about Giardia infections. May 2024 [internet publication].Texto completo

Shane AL, Mody RK, Crump JA, et al. 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea. Clin Infect Dis. 2017 Nov 29;65(12):e45-80.Texto completo Resumo

Artigos de referência

Uma lista completa das fontes referenciadas neste tópico está disponível para os usuários com acesso total ao BMJ Best Practice.

Diagnósticos diferenciais
- Rotavirus or other viral gastroenteritis
- Functional diarrhea
- Celiac disease
Mais Diagnósticos diferenciais
Diretrizes
- CDC Yellow Book: health information for international travel - giardiasis
- Infectious diarrhea: guideline for investigation
Mais Diretrizes
Folhetos informativos para os pacientes
Diarrhea in adults
Mais Folhetos informativos para os pacientes
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Giardiasis

Summary

Definition

History and exam

Key diagnostic factors

Other diagnostic factors

Risk factors

Diagnostic tests

1st tests to order

Tests to consider

Treatment algorithm

nonpregnant adult or child

pregnant; first trimester

pregnant; second or third trimester

treatment failure or resistance

Contributors

Authors

Luther A. Bartelt, MD

Disclosures

Acknowledgements

Disclosures

Peer reviewers

Zana Nikolla, MD

Disclosures

Rodney Adam, MD

Declarações

Créditos aos pareceristas

Declarações

Referências

Principais artigos

Artigos de referência

Uma lista completa das fontes referenciadas neste tópico está disponível para os usuários com acesso total ao BMJ Best Practice.

Diagnósticos diferenciais

Diretrizes

Folhetos informativos para os pacientes

Conectar-se ou assinar para acessar todo o BMJ Best Practice

Conectar-se ou assinar para acessar todo o BMJ Best Practice

Conectar-se para acessar todo o BMJ Best Practice