What is giardiasis?

Giardiasis, an intestinal illness, is caused by a microscopic parasite called Giardia lamblia . In 2008, there were 840 cases reported among New York City residents (rate of 10.2 cases per 100,000 persons).

Who gets giardiasis?

Anyone can get giardiasis. However, it tends to occur more often in people residing in institutional settings, diaper-aged children in day care centers, child care workers, parents of infected children, foreign travelers, and individuals who drink improperly treated surface water (such as from lakes, rivers, or streams) or who swim in contaminated water. Men who have sex with men may also be at increased risk of contracting giardiasis.

How is giardiasis spread?

The parasite is passed in the stool (feces) of an infected person or animal. When it is outside the body, it is protected by an outer shell, and can survive in the environment for long periods of time. It may contaminate soil, water, food or surfaces. People become infected by swallowing the parasite. Person-to-person transmission may occur in day care centers or other settings where hand-washing practices are poor. Sexual practices in which the mouth or hand comes into contact with a partner's anus or stool may result in spread.

Where are the Giardia parasites found?

Giardia has been found in infected people (with or without symptoms) and wild and domestic animals. The beaver has gained attention as a potential source of Giardia contamination of lakes, reservoirs, and streams, but human fecal wastes may be just as important.

What are the symptoms of giardiasis?

People exposed to giardia may experience mild or severe diarrhea, abdominal cramps, bloating, and fatigue. In some instances, there may be no symptoms at all. Fever is rarely present. Occasionally, chronic diarrhea may develop over several weeks or months, with significant weight loss. In otherwise healthy persons, symptoms may last 2 to 6 weeks.

How soon after infection do symptoms appear?

The symptoms may appear from 3 to 25 days after exposure, but usually within 10 days.

How long can an infected person carry Giardia ?

The carrier stage generally lasts from a few weeks to a few months. Treatment with specific antibiotics may shorten the carrier stage.

How is giardiasis diagnosed?

Diagnosis is made by examining the stool under a microscope or by using special detection tests for Giardia . Sometimes, several stool samples obtained on different days are necessary, since the number of Giardia parasites shed in the stool varies from day to day.

What is the treatment for giardiasis?

Anti-infective drugs such as metronidazole, tinidazole, or nitazoxanide are often prescribed by doctors to treat giardiasis. Drug resistance or relapse may occur with any drug. Some individuals may recover on their own without medication. Although Giardia can infect all people, young children and pregnant women may be more susceptible to the dehydration caused by diarrhea and should drink plenty of fluids while ill.

Should an infected person be excluded from work or school?

Since the Giardia parasite is passed in the stool, people with active diarrhea who are unable to control their bowel habits (for example, infants, young children, and certain disabled individuals) may need to be excluded from group settings where they present a risk to others. Most infected people may return to work or school when their stools become formed as long as they wash their hands thoroughly after using the toilet. Food handlers, certain health care workers, children in day care, pre-kindergarten or kindergarten, and employees in day care, pre-kindergarten and kindergarten must obtain approval from the Health Department before returning to their routine activities, even if they are not having diarrhea. This requires follow-up stool testing to be sure that they are no longer infectious.

How can giardiasis be prevented?

The most important preventive measures include:

Practice good hygiene.

  • Always thoroughly wash hands with soap and water before handling food, after using the toilet or changing diapers, after handling animal stools, and after gardening or other direct contact with soil.
  • If you work in a child-care center where you change children's diapers, wash hands carefully between changing each child's diapers. When using gloves, wash your hands and change gloves between each child. If you take care of persons with giardiasis, or persons who have diarrhea, wash your hands after bathing patients, emptying bedpans, changing soiled linen, or otherwise coming in contact with stool.

Avoid water that may be contaminated.

  • Do not drink water directly from streams, lakes, springs or swimming pools.
  • If there is a possibility of Giardia contamination in a drinking water source, you can make the water safe to drink by: (1) Heating water to a rolling boil for 1 minute, or (2) Using a water filter that has an absolute pore size of at least 1 micron or smaller, or one that has been National Sanitation Foundation (NSF) rated for "cyst removal."

Avoid food that may be contaminated.

  • Uncooked fruits and vegetables should be washed thoroughly before being eaten.

Take extra care when traveling.

  • If you travel to developing countries, you may be at greater risk for giardiasis because of poorer water treatment and food sanitation. Avoid raw fruits and vegetables that you did not wash or peel yourself, unboiled tap water, ice made from unboiled tap water, and items purchased from street vendors.

Protect yourself and others.

  • Carefully dispose of sewage wastes so as not to contaminate surface water or ground water.
  • If you have giardiasis, wash your hands often to prevent spreading the disease to other people.
  • If you have diarrhea, protect others by not swimming. Persons with diarrhea should not use public swimming facilities. If you have giardiasis, do not swim in recreational waters while experiencing diarrhea and for at least 2 weeks after the diarrhea stops. You can pass Giardia in your stool and contaminate water for several weeks after your symptoms have ended.
  • Sexual practices that may result in hand or mouth contact with stool, such as anal sex, touching the anus, or oral-anal sex ("rimming"), increase the risk for giardiasis transmission. Risk of transmission may be decreased by washing thoroughly with soap and water before and after any anal contact, and by using a barrier such as a dental dam or household plastic wrap during oral-anal contact. Persons who are infected with giardiasis, or any diarrheal illness, should refrain from sexual activity that may expose a partner to their stool until they are effectively treated.

Last updated December 2009.