Infectious Diseases A to Z – Giardiasis

With this new column, Elite Healthcare will compile an index of various infectious diseases, with occasional highlights of emerging conditions.


General definition and information: A common intestinal parasite most prevalently experienced by those who live in countries with poor sanitary conditions, poor water quality control, and overcrowding. This condition is not unique to these populations, however. Also a common cause of infection among hikers and campers who drink water from streams and other potentially contaminated sources, giardiasis may be referred to as “beaver fever,” following an outbreak at Banff National Park in Canada when hikers became ill after drinking stream water that had been contaminated with giardia, the microscopic parasite that causes the diarrheal illness, from beavers.1 Giardia is found on surfaces or in soil, food, or water that has been contaminated with feces from infected humans or animals.

Symptoms include a variety of intestinal complications, including diarrhea, gas or flatulence, greasy stool that can float, stomach or abdominal cramps, upset stomach or nausea, and dehydration. According to the Centers for Disease Control and Prevention (CDC), the infection has become recognized as a common cause of waterborne disease in humans in the United States over the last 30 years. Symptoms may also lead to weight loss, although some people who are infected will not display any symptoms.

Causes & Modes of Transmission:

Once a person or animal has been infected with giardia, the parasite lives in the intestines and is passed in feces.2 Once outside the body, giardia can sometimes survive for weeks or months.2 Symptoms in humans normally begin 1-3 weeks after infection occurs, according to the CDC. While it is not possible to contract giardiasis through contact with blood, the condition can be spread by swallowing giardia that is picked up from surfaces, including bathroom handles, changing tables, diaper pails, and toys that contain feces from an infected person or animal.2 Eating uncooked food that contains giardia organisms is another transmission route. According to the CDC, other populations that are more susceptible to become infected with giardiasis include:

  • children, especially diaper-aged children, in childcare settings
  • people who come into close contact with those infected with giardiasis (eg, people living in the same household), including caregivers and healthcare providers
  • people who rely on water from lakes, streams, or wells for their drinking water or ice
  • people who swallow water while swimming and playing in recreational water where Giardia may live
  • international travelers
  • people exposed to human feces through sexual contact.

A stool sample will be used to test for positive infection. Testing for the condition can be difficult to determine, according to the CDC, and may result in the patient being asked to submit several stool specimens collected over several days in order to appropriately detect. Among patients who are otherwise healthy, symptoms of giardiasis can be expected to persist for 2-6 weeks, although symptoms may last longer.

Treatment Strategies:

For those infected individuals who are not displaying any symptoms of the condition, the CDC suggests that treatment may not be warranted. Exceptions to this generalization, however, include symptoms of nausea and/or upset stomach even when diarrhea is not present, as well as instances of tiredness, weight loss, and/or a lack of hunger despite there being no symptoms of diarrhea. Treatment may also be indicated in instances where one or more family members are sick with the condition, or if a family member is pregnant and, according to the CDC, which also notes that treatment among those women who are pregnant may be different than it is for other patients.

Certain medications can help decrease the length of time symptoms last. Options include:3

  • Metronidazole, the most commonly used antibiotic for giardia infection;
  • Tinidazole; and
  • Nitazoxanide, which is available as a liquid and therefore may be easier for children to swallow.

Prevention Parameters:

According to the CDC, prevention methods include practicing good hygiene, avoiding contaminated water, avoiding foods that may be contaminated, and avoiding contact and contamination with feces during sex. When it comes to the presence of the parasite in drinking water, waste can be problematic through a number of different means, including sewage overflow, sewage systems that are not working properly, polluted stormwater runoff, and agricultural runoff.4 The CDC advises that wells may be more vulnerable to contamination after flooding, particularly if the wells are shallow, have been dug or bored, or have been submerged by floodwater for long periods of time.4

Patients who suspect potential problems with their drinking water that comes from a private well should be directed to contact their respective state’s certification official. (The United States Environmental Protection Agency offers a resource for a listing of laboratories that will perform tests on drinking water for a fee.5)

There are also strategies that may be used to remove the parasite from drinking water, as offered by the CDC:4

  • Bring water to a rolling boil for one minute (at elevations above 6,500 feet, boil for three minutes).
  • Water should then be allowed to cool, stored in a clean, sanitized container with a tight cover, and refrigerated.

An alternative to boiling water is using a point-of-use filter, according to the CDC, which also warns that not all home water filters will remove Giardia. Filters that are designed to remove the parasite should include specific labels that can be found online as a resource offered by the CDC.4

Patients should also be advised to contact their local health department for recommended procedures and to have their well water tested at least once per year.


  1. Giardiasis. Ontario Ministry of Health and Long-Term Care. 2015. Accessed online:
  2. General information. Centers for Disease Control and Prevention. 2015. Accessed online:
  3. Giardia infection (giardiasis). Mayo Clinic. 2019. Accessed online:
  4. Giardia and drinking water from private wells. Centers for Disease Control and Prevention. 2015. Accessed online:
  5. Certification of laboratories that analyze drinking water samples to ensure compliance with regulations. Environmental Protection Agency. 2019. Accessed online:

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