SynopsisCodesLook ForDiagnostic PearlsDifferential Diagnosis & PitfallsBest TestsManagement PearlsTherapyReferences

Information for Patients

View all Images (2)

Other Resources UpToDate PubMed


Contributors: James J. Douglas MD, FRCPC, Ricardo M. La Hoz MD, James H. Willig MD, MSPH
Other Resources UpToDate PubMed


Giardia lamblia, also known as Giardia duodenalis or Giardia intestinalis, is a flagellated enteric protozoan and a common cause of diarrhea (endemic and epidemic) throughout the world. In the United States, G lamblia has been demonstrated in 4%-7% of stool specimens, making it the most commonly identified intestinal parasite. There is a bimodal distribution, with the illness being reported most frequently in children aged 1-9 years and adults aged 35-45. Disease prevalence is highest during late summer and fall.

The parasite is spread via the feces of an infected person or animal. Acquisition occurs when cysts are ingested via contaminated water or food, or via person-to-person contact. After excystation, trophozoites colonize and multiply in the small bowel and may disrupt epithelial brush border, mucosally invade, or elaborate an enterotoxin. The incubation is usually 7-14 days, with symptoms often lasting more than 2-4 weeks; however, patients may continue to shed cysts for 6 months or longer.

  • Prolonged diarrhea – more than 7-10 days
  • Malaise
  • Flatulence
  • Foul-smelling, greasy stools
  • Sulfuric belching
  • Abdominal cramps
  • Bloating
  • Nausea
  • Vomiting
  • Malabsorption
  • Weight loss
Risk factors:
  • Travel to endemic regions
  • Children in daycare
  • Men who have sex with men


A07.1 – Giardiasis [lambliasis]

58265007 – Giardiasis

Look For

Subscription Required

Diagnostic Pearls

Subscription Required

Differential Diagnosis & Pitfalls

Best Tests

Subscription Required

Management Pearls

Subscription Required


Subscription Required


Subscription Required

Last Updated:10/18/2022
Copyright © 2023 VisualDx®. All rights reserved.
Patient Information for Giardiasis
Print E-Mail Images (2)
Contributors: Medical staff writer


Most foodborne illness, also known as food poisoning, comes from bacteria in food that has multiplied, either from poor handling, improper cooking, or poor storage of food. Other things, such as toxins, parasites, chemicals, and viruses, can contaminate food.

Giardiasis comes from an intestinal parasite. It is obtained by eating or drinking contaminated food or water.

Who’s At Risk

Foodborne illness can occur in any person shortly after ingestion of contaminated food. Illness may occur when a person complains that food he/she has eaten "didn't taste right" or ate food that was old, improperly prepared, or was left at room temperature for more than 4 hours. There may be no indication that food or water has been contaminated until the symptoms of illness occur.

Certain people are more prone to foodborne illness than others, such as:
  • Elderly adults – Older age plays a factor in sensitivity to foodborne illness because the immune system becomes slower to respond and weaker with increasing age.
  • Infants / young children – Younger age plays a factor in sensitivity to foodborne illness as well, as young children and infants' immune systems are not fully developed.
  • Others with lowered immune systems – People with diabetes, those with AIDS, those going through therapy for cancer (ie, radiation or chemotherapy), and those who are pregnant.
Giardiasis is more common in Brazil, Cuba, India, Russia, and Serbia, but it is found all over the world, including in the United States.

Signs & Symptoms

Within hours or days of eating contaminated food, symptoms generally include diarrhea, nausea, abdominal pain, fever, and, sometimes, vomiting. Foodborne illness is often mistaken for the flu, as the symptoms are similar.

Self-Care Guidelines

If you become sick from foodborne illness, resting and drinking plenty of liquids is key. Drink Gatorade or water to prevent dehydration.

Foodborne illness can be prevented by following these general guidelines:
  • Wash your hands before handling food.
  • Wash your hands after using the toilet, changing diapers, smoking, blowing your nose, coughing, or sneezing.
  • Wash your hands after touching raw meat or eggs.
  • Use plastic (rather than wooden) cutting boards for cutting raw meats.
  • Thoroughly clean all surfaces and utensils that came into contact with uncooked meat or eggs.
  • Cook meats and eggs thoroughly before eating.
  • Do not eat or drink foods made from raw or undercooked eggs, meats, or unpasteurized dairy products.
  • Wash all produce thoroughly before eating.
  • Avoid cross-contamination of foods by keeping produce, cooked foods, and ready-to-eat foods separate from uncooked meats and raw eggs.

When to Seek Medical Care

Seek professional medical care if you suspect you have giardiasis and one or more of the following is true:
  • Your symptoms last for more than 2 weeks.
  • Prolonged diarrhea leads to weight loss.
  • You have recently traveled to South America, India, or the former Soviet Union.
  • Your children are in day care.


Your doctor will prescribe anti-parasitic medication. Pregnant women with mild giardiasis may instead be maintained with hydration and nutritional support until after the first trimester, when it is safer for anti-parasitic medicine to be taken.
Copyright © 2023 VisualDx®. All rights reserved.
A medical illustration showing key findings of Giardiasis (Acute) : Diarrhea, Fever, Vomiting, Abdominal cramp, Contaminated drinking water exposure, Anorexia, Steatorrhea, Flatulence
Copyright © 2023 VisualDx®. All rights reserved.