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Patient education: Giardia (Beyond the Basics)

Karin Leder, MBBS, FRACP, PhD, MPH, DTMH
Section Editor
Peter F Weller, MD, MACP
Deputy Editor
Elinor L Baron, MD, DTMH
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Giardia (also called giardiasis or Giardia infection) is an infection of the gastrointestinal tract caused by a microscopic organism called Giardia lamblia. This parasite, which also goes by the names Giardia duodenalis or Giardia intestinalis, resides in the gut and can cause diarrhea and stomach discomfort (nausea, stomachache). It is one of the most common gastrointestinal parasites; an estimated 1.2 million cases occur annually in the United States.

Giardia can affect people of all ages, but it is especially common in children younger than five years old. It is also seen in internationally adopted children and among people who travel in resource-limited settings.

The Giardia organism is found in the feces of infected people and can spread because of poor sanitation or because drinking water or food becomes contaminated. It can also infect animals, such as dogs, cattle, and sheep.

How Giardia is spread — Giardia infections can spread in three ways, all of which can be prevented. (See "Giardiasis: Treatment and prevention".)

Waterborne transmission — Waterborne transmission is the most common route of infection. People who drink from contaminated streams, reservoirs, or wells can become infected. Contaminated water used to prepare drinks or wash raw food can also be a source of infection.

Waterborne transmission is especially likely among campers and hikers who drink from untreated water sources (streams, lakes) and among people traveling in regions where water sanitation standards may not be adequate to eliminate the organism.

Foodborne transmission — The organism that causes Giardia is killed by cooking, so properly cooked food rarely leads to infection. However, uncooked food or food that is contaminated after cooking can cause Giardia infections. (See "Patient education: Food poisoning (foodborne illness) (Beyond the Basics)".)

Person-to-person transmission — Person-to-person transmission can happen when traces of infected feces travel between two people. This can happen if someone does not thoroughly wash their hands after using the bathroom or after changing the diapers of an infected child. Person-to-person transmission is the cause of outbreaks in families and institutions, such as daycare centers and nursing homes. Person-to-person transmission can also happen during anal sex or during sex play involving the anus.


Giardia infections do not always cause symptoms. Some people carry the organism without ever knowing it. Some people develop symptoms and then get better without treatment because they combat the infection on their own. When symptoms do arise, they can include:

Diarrhea that comes on suddenly and may be initially watery

Malaise (a vague feeling of discomfort) or fatigue

Foul-smelling and fatty stools

Abdominal cramps, gas, and bloating

Nausea or vomiting

Weight loss

People generally develop these symptoms one to two weeks after being exposed to Giardia, and the symptoms often last at least two to four weeks. Some people develop a chronic form of Giardia that lasts even longer, although symptoms tend to be less severe.

Nutritional problems — Giardia can also interfere with the way the body absorbs nutrients, so it can cause vitamin deficiencies and other nutritional problems. In up to 40 percent of cases, Giardia impairs the body's ability to digest lactose, the form of sugar found in milk, cheese, and other dairy products. Guidance about lactose products is included below. (See 'Recurrence of symptoms' below.)


If your healthcare provider thinks you may have Giardia, he or she will ask you for a stool sample and then send it to the lab. There, technicians will examine the stool to test for any parasites that might be present. (See "Giardiasis: Epidemiology, clinical manifestations, and diagnosis".)

You may need to provide more than one stool sample before the infection shows up on a test. Depending on your individual situation, your doctor might also recommend additional tests, such as endoscopy.


Treatment for Giardia involves taking an antibiotic for at least one day or several days. In most cases, that is enough to eliminate the infection and its symptoms. In stubborn cases that do not improve with the first round of antibiotics, doctors sometimes recommend changing the type, dose, or duration of treatment.

If you do not have symptoms of Giardia but testing shows that you are infected, you may not need antibiotic treatment. However, children in daycare and people who handle food should be treated for Giardia even if they have no symptoms to prevent the spread of infection.

Avoid swimming in pools, hot tubs, lakes, rivers, and the ocean until one week after you have finished treatment for Giardia. Do not go swimming if you still have diarrhea. Swimming can contaminate the water and cause others to become ill. Avoid all types of anal sex until treatment has been completed.

If your symptoms resolve after you finish your antibiotic treatment, you do not need to be tested for Giardia again.

Special considerations for children — Antibiotics are the most important part of Giardia treatment both in children and adults, but children sometimes need additional care. Diarrhea can cause dehydration and a salt imbalance, both of which can be especially tough on children. For them, drinks containing electrolytes may be recommended to restore what is lost through diarrhea. Fluid and electrolyte replacement are discussed in detail separately. (See "Patient education: Acute diarrhea in children (Beyond the Basics)".)

The safety of breastfeeding while being treated for Giardia depends upon which antibiotic is used; some antibiotics are safe to take while breastfeeding while others are not. If you are breastfeeding, ask your healthcare provider if you can safely breastfeed while taking your antibiotics. (See "Patient education: Maternal health and nutrition during breastfeeding (Beyond the Basics)", section on 'Medication safety with breastfeeding'.)

Recurrence of symptoms — After being treated for Giardia and seeing symptoms improve, some people experience a relapse. This can happen because people consume dairy products too soon or because they are still infected with Giardia.

Giardia can interfere with the body's ability to digest dairy products (see 'Nutritional problems' above). Even once the infection is gone, it can take several weeks before normal digestion returns. For this reason, patients may wish to avoid milk, cheese, yogurt, and any other foods that contain lactose for at least a month following treatment (table 1).

If you or your child develop symptoms again after being treated for Giardia, your healthcare provider will want to run another stool test to determine if Giardia is causing the problem. If Giardia shows up again, it could be that the first round of treatment did not get all the organisms or it could be that you or your child were reinfected somehow. Work with your healthcare provider to root out the possible source of the infection and ask about how you can prevent future infections.


The key to preventing Giardia and other infections is good hygiene. Here are some good hygiene tips:

Wash your hands with soap and water before eating and after using the bathroom, and teach children to do the same.

Wash your hands with soap and water after changing diapers or after tending to anyone who has poor bowel control.

Dispose of diapers properly and wash any clothes that could be contaminated with even small amounts of feces.

Try not to swallow water when swimming.

Pre-treat drinking water when traveling or hiking. This can be done by:

Boiling drinking water for at least 10 minutes at a hard boil.

Adding five drops of tincture of iodine to a quart of water and waiting 30 minutes. Iodine is much more effective in eliminating Giardia than chlorine-based (bleach) treatments.

Using a high-quality water filtration system. Information about water purification and a traveler's guide for buying water filters is available at the United States Centers for Disease Control and Prevention website.

Use proper food preparation etiquette. Food preparation and safety tips are discussed separately. (See "Patient education: Food poisoning (foodborne illness) (Beyond the Basics)".)


Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient education: Giardia (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient education: Food poisoning (foodborne illness) (Beyond the Basics)
Patient education: Acute diarrhea in children (Beyond the Basics)
Patient education: Maternal health and nutrition during breastfeeding (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Antiprotozoal therapies
Giardiasis: Epidemiology, clinical manifestations, and diagnosis
Giardiasis: Treatment and prevention

The following organizations also provide reliable health information.

National Library of Medicine


National Institute of Digestive and Diabetes and Kidney Diseases


Center for Disease Control and Prevention


American College of Gastroenterology




The editorial staff at UpToDate would like to acknowledge Flor Munoz, MD, who contributed to an earlier version of this topic review.

Literature review current through: Nov 2017. | This topic last updated: Tue Sep 05 00:00:00 GMT+00:00 2017.
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