Giardia Infection

Medically Reviewed By William C. Lloyd III, MD, FACS
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What is giardia infection?

Giardia is the name of a parasite that is scientifically known as Giardia lamblia. This parasite causes a contagious disease, called giardiasis, by infecting the intestinal tract of humans, resulting in nausea, vomiting, diarrhea, and other gastrointestinal symptoms.

Giardia infection is the most common intestinal parasitic disease in the United States. About 2% of adults and 6% to 8% of children in the United States and other developed countries have had giardia infection. In contrast, up to one-third of people in developing countries have been infected (Source: CDC).

Giardia spreads among humans through contaminated food and water. Most commonly, people become infected with giardia from drinking untreated, contaminated water from streams, lakes or ponds. Once a person is infected, the parasite lives in the intestines and is passed in the stool of the infected person. Animals such as cats, dogs and cattle can also be infected and spread the disease to humans. Within industrialized countries, Giardia outbreaks are common in day care centers where the disease is spread by direct contact and substandard hygienic practices.

The signs and symptoms of giardia infection can last for one to two weeks or even longer. The disease course varies among individuals. Some people infected with giardia have no symptoms at all, while others may have severe diarrhea or vomiting that may pose a risk of dehydration. Fortunately, giardia infection can be treated successfully with antibiotics. Even better, you can reduce your risk of giardia infection by following commonsense hygiene practices, such as washing your hands with soap and water prior to preparing food and after handling dirty diapers or using the bathroom.

Left untreated, giardia infection may lead to severe dehydration. Severe dehydration and electrolyte imbalances can result in shock or coma and may be life threatening. Seek prompt medical care if you develop diarrhea and vomiting and believe you may have been exposed to giardia. Seek immediate medical care (call 911) if you, or someone you are with, have symptoms of severe dehydration, such as confusion, lethargy, loss of consciousness, cold skin, or reduced urine production.

What are the symptoms of giardia infection?

Giardia infection causes irritation and inflammation of the intestines that may result in a number of symptoms. The symptoms can vary in intensity among individuals.

Common symptoms of giardia infection

The most common symptoms of giardia infection are related to disturbances of the digestive system and include:

  • Abdominal bloating

  • Abdominal pain

  • Diarrhea (can be explosive and foul smelling)

  • Fever and chills

  • Flatulence

  • Nausea or vomiting

  • Weight loss

Other symptoms of giardia infection

As the infection progresses, symptoms of dehydration may develop. Symptoms related to the loss of fluid include:

Serious symptoms that might indicate a life-threatening condition

Rarely, dehydration resulting from giardia infection may be so severe that a life-threatening situation can develop. Seek immediate medical care (call 911) if you, or someone you are with, have any of the following symptoms:

  • Change in level of consciousness or alertness, such as passing out or unresponsiveness

  • Change in mental status or sudden behavior change, such as confusion, delirium, lethargy, hallucinations, and delusions

  • Decreased urine output

  • Fast heart rate (tachycardia)

  • High fever (higher than 101 degrees Fahrenheit)

  • Severe abdominal pain

  • Severe dizziness or sudden loss of balance

What causes giardia infection?

Giardia infection is caused by the parasite Giardia lamblia. The parasite is present in the stool (feces) of infected people and animals. When water sources are contaminated with feces containing giardia, drinking from these water sources spreads the parasite. For this reason, giardia infection occurs most frequently in people traveling to developing countries or in hikers and campers who have consumed untreated water from lakes, streams or ponds.

Giardiasis (infection with giardia) may also be spread by poor hygiene practices, such as touching infected human or animal feces without proper hand washing. It can also occur among children in day care settings and in people who have close contact with those who are already infected. It is also possible to contract giardia infection from oral-anal contact during sexual activity with an infected person.

What are the risk factors for giardia infection?

A number of factors increase your risk of developing giardia infection. Not all people with risk factors will get giardia. Risk factors for giardia infection include:

  • Attendance or work in a day care setting

  • Close contact with an infected person or animal

  • Consumption of untreated water from lakes, rivers or streams

  • Oral-anal sexual contact

  • Recreation in public swimming pools

  • Travel in countries where the infection is common

Reducing your risk of giardia infection

You can lower your risk of developing or transmitting giardia infection by:

  • Avoiding oral-anal contact during sex

  • Drinking only purified water when backpacking, camping or hiking

  • Drinking only purified water when visiting developing countries

  • Not swallowing water in swimming pools, hot tubs, or other recreational water sources

  • Using purified water for brushing your teeth and washing food when visiting developing countries

  • Washing your hands well with soap and water after touching feces, having contact with an infected person or animal, changing diapers, or using the bathroom, and before eating or preparing food

How is giardia infection treated?

Treatment for giardia infection begins with seeking medical care from your health care provider. To determine if you have giardia, your health care provider will ask you to provide stool samples for laboratory testing.

Antibiotic therapy is the mainstay of treatment for giardia infection and is highly effective. It is important to follow your treatment plan for giardia precisely and to take all of the antibiotics as instructed to avoid re-infection or recurrence.

Antibiotic medications that are effective in the treatment of giardia infection include:

  • Metronidazole (Flagyl)
  • Nitazoxanide (Alinia)
  • Tinidazole (Tindamax)

If you have diarrhea and vomiting, fluid and electrolyte replenishment is also a component of successful treatment.

What you can do to improve your giardia infection

In addition to following your health care provider’s instructions and taking all medications as prescribed, you can speed your recovery by:

  • Ensuring adequate hydration by drinking plenty of water and electrolyte solutions
  • Getting plenty of rest

If you have a giardia infection, it is important to practice good hygiene to avoid spreading the infection to those who have close contact with you. Wash your hands frequently with soap and water after using the bathroom or touching any contaminated bedding or clothing. Do not use public pools, hot tubs, or recreational water facilities until your infection has cleared.

What are the potential complications of giardia infection?

Dehydration, a possible complication of giardiasis, can be serious and even life threatening in some cases. You can minimize your risk of serious complications by following your treatment plan and taking all medications as prescribed.

Although these complications are rare with giardia infection, left untreated, severe dehydration can lead to serious consequences including:

  • Acute renal (kidney) failure=
  • Coma
  • Electrolyte disturbances (loss of sodium potassium, chloride, and bicarbonate)
  • Malabsorption syndrome
  • Shock
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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jan 18
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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