Giardiasis is a common illness caused by a parasite that may result in diarrhea and stomach cramps. The Giardia parasite can spread through contaminated water, food and surfaces, and from contact with someone who has it. Antibiotics can treat giardiasis.


What is giardiasis?

Giardiasis is an intestinal infection caused by a microscopic parasite called Giardia. This parasite lives all over the world, especially in bodies of water. If you accidentally swallow it, it takes up residence in your small intestine and multiplies, feeding off the nutrients there. This can cause a variety of intestinal symptoms, including foul-smelling diarrhea, bloating and gas, stomach cramps, nausea and fatigue.

Giardiasis symptoms can be mild to severe, and some people never have symptoms. The infection typically clears by itself after a few weeks, but people with weaker immune systems may have a harder time clearing it. A healthcare provider can prescribe antiparasitic medications for giardiasis if you need them. Sometimes, people continue to have symptoms for weeks to months after the infection has gone.

How common is giardiasis?

Giardiasis is common throughout the world. It’s the most common parasite infection in the U.S., where it affects over a million people each year. In developed countries in general, it affects an estimated 10% of the population. In developing countries, giardiasis affects an estimated one-third of the population.

Giardia thrives in regions and environments with less public sanitation, especially in natural bodies of water and inadequately sanitized public water supplies. Children are more often infected than adults, especially those under the age of 4. In the U.S., childcare centers are a frequent source of outbreaks.


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Symptoms and Causes

What are the symptoms of giardiasis?

About half of people never develop symptoms of giardiasis. Among those who do, common symptoms include:

Less common symptoms can include:

Long-term effects

Most people have short-term symptoms during their infection, but occasionally, some people have longer-lasting or recurring symptoms. They might develop dehydration and weight loss from the chronic diarrhea and nausea. Sometimes, they develop lasting digestive difficulties, like lactose intolerance.

What causes giardiasis?

Giardia infection happens when you accidentally ingest the microscopic parasite during the cyst stage of its life cycle. The Giardia cyst is sort of like an egg that can survive in the wild until it finds a body (host) to hatch in. After you swallow it, the cyst settles and “hatches” in your small intestine. The parasite feeds off your nutrients and multiplies. After this, it changes back into a cyst and passes out in your poop.


How is giardiasis transmitted to humans?

Animals and humans both get giardiasis, and they can both pass it on to others through their poop. The Giardia cyst lives within microscopic traces of poop within your environment that are too small to see. These traces can linger on surfaces, in bodies of water and on people’s hands if they don’t wash them well enough after using the bathroom. They can also transfer to people’s food and drinking water.

Some common ways you might get giardiasis include:

How long does giardiasis take to kick in, and how long does it last?

The incubation period for giardiasis is one to two weeks from infection. That’s how long it takes for the Giardia cyst to release the parasite and for the parasite to begin to multiply, alerting your immune system. When your immune system activates to remove it, that’s when you might begin to notice symptoms. Symptoms typically last between two and six weeks, but in some people, they can last longer.


What does giardiasis do to you?

Giardia infection doesn’t always cause noticeable symptoms, but it can. Some symptoms are due to the parasite itself, and others are due to your body activating to remove the parasite. For example, the parasite feeding off your nutrients might sap your energy, making you feel increasingly tired. Diarrhea, swelling and skin reactions are symptoms of inflammation, part of your immune system’s response.

These symptoms are short-lived for most people. They go away when the infection does. But if giardiasis lasts a long time, or keeps coming back, it can do more long-term damage. This might happen if you have a weaker immune system, possibly from a preexisting health condition. In developing countries, malnutrition and lower health status can make people more vulnerable to complications from giardiasis.

What are the possible complications of giardiasis?

Possible complications include:

  • Dehydration. Dehydration is the primary short-term risk from giardiasis, and it can also happen gradually over the long term. Anyone who’s having diarrhea and/or vomiting loses a lot of fluids. It can be hard to replace the fluids as fast as you’re losing them. Children and people over age 65 are especially vulnerable to dehydration, so it’s important for caretakers to stay alert.
  • Gastrointestinal disease. If giardiasis lasts a long time, it can damage the lining of your small intestine. This can cause chronic gastrointestinal symptoms and trigger irritable bowel syndrome. It can also damage your intestine’s ability to absorb the nutrients in your food. You could develop nutritional deficiencies. This could affect growth and development in children.
  • Autoimmune disease. In some people with severe and/or chronic giardiasis, long-term inflammation triggers an autoimmune response. This means that part of your immune response to the infection becomes hyperactive and automatic, continuing even after the infection is gone. Some people have developed reactive arthritis, chronic fatigue syndrome or new food allergies.

Diagnosis and Tests

How is giardiasis diagnosed?

A healthcare provider can diagnose giardiasis by testing a sample of your poop for evidence of Giardia. This might take a few tries because you might pass the cysts in your poop one day but not the next. It’s not always necessary to identify giardiasis this way, though. Healthcare providers often prescribe medications to treat giardiasis based on your symptoms alone, without needing to diagnose it first.

Management and Treatment

What medications or other treatments do healthcare providers prescribe for giardiasis?

Not everyone will need treatment for giardiasis. But if you have symptoms, your healthcare provider can prescribe antiparasitic medications to make the infection go away faster. With medications, most people feel better within a week. But underlying medical conditions can affect your response. If your condition is more severe, you might need additional support, like rehydration or antidiarrheal medications.


Antibiotics for giardiasis include:

Different medications affect different people in different ways. If your first prescription doesn’t work or causes intolerable side effects, your provider will offer an alternative. Your provider might recommend that everyone in your household take them to prevent the infection from spreading. If you’re pregnant, they might recommend delaying treatment because these drugs could potentially be toxic to the fetus.

Can Giardia go away on its own?

Yes, giardiasis often goes away on its own, and if your symptoms are mild, your provider might encourage you to let it do that. When populations use certain antibiotics against common infections too often, the infections can begin to become resistant to those antibiotics. This is starting to occur in certain places with giardiasis. If you can go without medication, you can help prevent antibiotic resistance.

But giardiasis doesn’t always go away in everyone. And in some people, it can be very persistent. If you continue to have symptoms for longer than six weeks, visit your healthcare provider. They can test you to find out if you’re still infected, or if your symptoms are due to the after-effects of the infection. They can offer treatment for either the infection itself or your symptoms and screen you for complications.

What happens if Giardia is left untreated?

Untreated Giardia infection often goes away by itself. But if it doesn’t, it can cause long-term complications for your digestive system, and even your immune system. It’s important to see a healthcare provider if you have symptoms lasting longer than six weeks. If your provider prescribes antibiotics, it’s important to take the full course to make sure the infection doesn’t rebound.

What happens if the treatment doesn’t work?

If you’ve taken antibiotics but testing later finds you’re still infected, it’s possible that:

  • You didn’t take the full course or you need a stronger dose.
  • You’ve been reinfected through your environment.
  • You need a different medication or combination.
  • You have a weakened immune system for some reason.

Your healthcare provider will investigate these possibilities. If you have an immune deficiency, you might need separate treatment for that. If necessary, your provider will consult an infectious disease specialist to devise an individualized treatment plan for you that combines different types of medications.


How can I lower my risk of getting or spreading giardiasis?

It’s hard to avoid something in your environment that’s too small to see. But there are steps that individuals and communities can take to prevent infection and reduce transmission of Giardia to others. For example:

  • Personal hygiene: Practice frequent hand washing to prevent germs from spreading, especially before eating or having sex and after using the bathroom or interacting with soil or animals.
  • Household hygiene: Clean and disinfect the bathrooms in your home regularly. If someone in your household has been sick, clean and disinfect everything they’ve touched, including linens.
  • Safe food practices: Wash fruit and vegetables in clean water before eating. Avoid raw foods and unbottled water when traveling abroad, where the local water might be contaminated.
  • Safe water use: Be wary when swimming in natural ponds, streams, lakes and swimming holes, and even public swimming pools if they don’t have a filtering system. Chlorine and iodine treatments aren’t always enough to kill Giardia. Try not to get any water in your mouth.

Outlook / Prognosis

What can I expect if I get giardiasis?

About half of people who get giardiasis never have symptoms. For those who do, they’re usually mild and temporary. If your symptoms are noticeable, your healthcare provider can prescribe medications. With treatment, most people feel better within a week. Without treatment, it might take two to six weeks.

Some people sometimes have a harder time with giardiasis. They might have more severe symptoms or might need extra help clearing the infection. If the parasite significantly damages your small intestine, you might continue to have gastrointestinal symptoms for a long time, even after the infection has gone away.

Living With

When should I see a healthcare provider about giardiasis?

Contact a healthcare provider if:

  • Your symptoms aren’t improving fast enough and you’d like treatment.
  • You or someone in your care has signs of dehydration.
  • Your medications cause intolerable side effects.
  • Your symptoms haven’t improved after taking medications.

A note from Cleveland Clinic

Preventive measures like hand washing and water filtering can go a long way toward protecting you and others from giardiasis. But Giardia is common everywhere, and it’s not always possible to avoid it. In most cases, the infection is mild and temporary, and you might not even need treatment. But don’t hesitate to seek treatment if you do need it, or follow up with your healthcare provider if the treatment isn’t working as expected.

Medically Reviewed

Last reviewed on 05/07/2024.

Learn more about our editorial process.

Appointments 216.444.7000