Giardia: A Traveler's Guide to Symptoms, Treatment, and Prevention

Giardia is a microscopic parasite that lives in the gut and causes giardiasis, an intestinal infection whose signature is diarrhea that is often greasy, foul-smelling, and prone to floating. You usually get it by swallowing contaminated water or food, or through person-to-person spread, and it takes only a few germs to make you sick. Symptoms typically start one to two weeks after exposure, which is why giardia frequently shows up late in a trip or even after you fly home. The classic cluster is diarrhea, gas, bloating, stomach cramps, nausea, and fatigue, usually without a high fever. The good news: giardia is curable. A clinician can prescribe a short course of medication such as tinidazole, metronidazole, or nitazoxanide that clears the infection in most people. Prevention comes down to safe water (boil or filter), thorough handwashing, and the same food-and-water habits that prevent traveler's diarrhea.

What Is Giardia?

Giardia is the everyday name for Giardia duodenalis, a single-celled parasite that lives in the intestines of infected people and animals and passes out of the body in stool. The illness it causes is called giardiasis. The parasite travels in a tough, dormant form called a cyst, which can survive for weeks to months in soil and water, including cold, clear-looking streams and lakes. When you swallow those cysts, they wake up in your small intestine and start the cycle again.

This is not an exotic, far-flung infection. According to the CDC, giardia is found in every region of the United States and around the world, and more people in the US get sick from giardia than from any other intestinal parasite, with more than 1 million cases each year. For travelers, the risk simply climbs in places with limited access to safe drinking water and in the backcountry, where untreated surface water is part of the trip.

One reassuring detail: although animals can carry giardia, you are unlikely to catch it from your dog or cat. The CDC notes that the strains that typically infect pets are usually different from the strains that make people sick.

Giardia Symptoms: What It Actually Feels Like

Giardia has a recognizable personality once you know what to look for. The infection tends to announce itself with diarrhea two to five times a day and a creeping, deepening tiredness. The most useful clue is the character of the stool: people often describe it as greasy or oily, unusually foul-smelling, and likely to float rather than sink, a result of the parasite interfering with fat absorption in the gut.

Common symptoms include:

• Diarrhea, often greasy, smelly, and floating
• Gas and bloating
• Stomach cramps or pain
• Nausea or an upset stomach
• Fatigue
• Dehydration from fluid loss
• Reduced appetite and, over time, unintended weight loss

A few features help distinguish giardia from a routine stomach bug. Fever is usually absent or mild. Symptoms can wax and wane, with a few better days followed by a relapse, which fools people into thinking they have recovered. And the bloating and "rotten egg" sulfur burps are distinctive enough that experienced travelers often suspect giardia before any test confirms it. Importantly, many infected people have no symptoms at all and can still pass the parasite to others.

How Long Does Giardia Last?

The timeline is part of what makes giardia such a sneaky travel illness.

Symptoms usually begin one to two weeks after you become infected. That incubation period is long enough that the contaminated lake water from your first day of trekking can produce diarrhea on day ten, or after you are already back home. If your stomach trouble starts more than a few days into a trip and drags on, giardia moves up the list of suspects.

Once symptoms start, giardiasis commonly lasts two to six weeks. That is considerably longer than most cases of bacterial traveler's diarrhea, which often improve within a few days. Occasionally, people develop long-term symptoms that can persist for months or even years if the infection is not treated, including ongoing diarrhea, malabsorption, and weight loss. Some people also develop temporary lactose intolerance after a giardia infection, so dairy can trigger symptoms for weeks even after the parasite is gone.

The practical takeaway: giardia rarely resolves quickly on its own, and waiting it out can mean weeks of misery. This is an infection worth treating rather than enduring.

How Travelers Catch Giardia

Giardia spreads by the fecal-oral route, which is a clinical way of saying that microscopic amounts of infected stool find their way into your mouth, usually through water, food, hands, or surfaces. Because swallowing just a few cysts can cause illness, the margin for error is small.

The most common routes for travelers are:

• Drinking untreated water. Springs, lakes, rivers, streams, and shallow wells can all carry giardia, even when the water looks pristine. This is the classic source for hikers, campers, and backcountry trekkers.
• Swallowing recreational water. Gulping water while swimming in lakes, rivers, pools, or splash pads can transmit the parasite.
• Contaminated food. Raw fruits and vegetables washed in contaminated water, or food handled by an infected person who did not wash their hands, can carry cysts.
• Person-to-person spread. Giardia passes easily in households, childcare settings, and anywhere hand hygiene is difficult. It can also spread through sexual contact involving exposure to stool.
• Contaminated surfaces and objects. Anything touched by unwashed hands after using the bathroom can become a vehicle.

Children are more likely to get sick than adults, and people with weakened immune systems are at higher risk of a prolonged or severe course. If you are traveling with kids, the combination of shared water, sandy hands, and crowded play spaces makes prevention especially worth the effort.

Where Giardia Is a Risk

Giardia exists everywhere, but the odds rise in specific situations. The two big risk categories for travelers are destinations with limited safe-water infrastructure and any trip that relies on untreated surface water.

That includes backpacking and trekking routes where you filter or treat water from streams, popular high-altitude trekking regions, rural stays in areas without reliable water treatment, and long-term or budget travel where you may not always control your water source. Giardia is a well-known cause of persistent diarrhea in travelers returning from South Asia, and it circulates widely across Africa, Latin America, and parts of Eastern Europe and the former Soviet states. It is also a genuine risk on North American and European wilderness trails, so "developed country" does not mean "safe stream."

If your itinerary involves camping, trekking, or rural travel, build water treatment into your plan the same way you pack rain gear. For destination-specific health risks, our destination health guides break down what to expect country by country.

How Giardia Is Diagnosed

If you suspect giardia, see a healthcare provider rather than guessing. Diagnosis is made by testing stool samples, since the parasite and its cysts are shed in poop. Because giardia is shed intermittently, a single sample can miss it, so clinicians often request more than one sample collected on different days. Modern stool antigen tests and molecular (PCR) panels have made detection faster and more reliable than older microscopy alone.

Tell your provider about your travel history, what water you drank, and how long symptoms have lasted. That context matters: persistent diarrhea lasting more than a week or two after travel, especially with greasy stools and bloating, points a clinician toward parasitic causes like giardia rather than the usual bacterial culprits.

Giardia Treatment: The Medications That Work

Giardia is treated with prescription antiparasitic medication, and most people recover fully once they take the right drug. There is no effective over-the-counter cure, which is one more reason to get evaluated rather than self-managing with anti-diarrheal pills alone. A clinician will choose a medication based on your age, pregnancy status, other medications, and how well you tolerate the options.

The three commonly used treatments are:

A few important points. First, do not drink alcohol while taking tinidazole or metronidazole or for three days afterward, because the combination can cause an unpleasant reaction with flushing, nausea, and vomiting. Second, rehydration matters as much as the antiparasitic: replace lost fluids and salts with oral rehydration solution while your gut recovers (our oral rehydration salts guide explains how to use it). Third, if dairy bothers you for a few weeks after treatment, that is the temporary post-giardia lactose intolerance mentioned earlier, and it usually fades on its own.

Pregnant travelers and young children need individualized treatment decisions, so the choice and timing of medication should always be made with a clinician.

How to Prevent Giardia While Traveling

Prevention is far easier than a three-week bout of greasy diarrhea on the road. Because giardia cysts are tough and can resist standard chemical disinfection, the cornerstone of prevention is treating your water properly and keeping your hands clean.

Make your water safe

Giardia cysts are notoriously resistant to chlorine and iodine at the doses used for field disinfection, which is exactly why "the water was treated" is not a guarantee. The two most reliable methods are:

For chemical treatment specifically, products that combine chlorine dioxide can perform better against cysts than plain chlorine or iodine tablets, but they still require long contact times. When in doubt, boil or filter.

Cover the rest of the fecal-oral route

• Wash your hands with soap and water at key times: after using the bathroom, after changing diapers, and before preparing or eating food. When soap is not available, an alcohol-based hand sanitizer helps, though it is less effective against cysts than soap and water.
• Avoid swallowing water while swimming in lakes, rivers, pools, and splash pads.
• Stick to standard food-and-water precautions: drink treated or sealed bottled water, skip ice of unknown origin, and avoid raw produce you cannot peel or that may have been washed in untreated water. Our food and water safety guide covers this in detail.
• If you or a travel companion has had diarrhea, wait several weeks after symptoms resolve before sexual activity that could involve exposure to stool, since the parasite can still spread during that window.

These habits do double duty: the same precautions that prevent giardia also lower your risk of bacterial traveler's diarrhea and other waterborne infections.

Giardia vs Regular Traveler's Diarrhea

Most traveler's diarrhea is bacterial, comes on fast, and improves within a few days, often with rest, fluids, and sometimes antibiotics. Giardia behaves differently, and the differences are clinically useful.

The single most helpful distinguishing clue is time. Diarrhea that begins a week or more into a trip, or after you return, and then lingers for weeks with greasy stools and bloating is much more likely to be giardia than a typical bacterial bug. If that pattern sounds familiar, ask a clinician about stool testing for parasites. For a broader comparison of the gut bugs travelers face, see our complete traveler's diarrhea guide.

When to See a Doctor

Contact a healthcare provider if you have diarrhea that lasts more than a few days, especially if it is greasy or foul-smelling, if you are losing weight, or if symptoms started a week or more after potential exposure to untreated water. Seek care sooner if you cannot keep fluids down, show signs of significant dehydration (very dark urine, dizziness, rapid heartbeat, or producing little urine), have a high fever, or see blood in your stool, since those features may point to a different or more serious problem.

Dehydration is the most immediate danger with any prolonged diarrheal illness, and it hits children and older travelers fastest. Replacing fluids and salts is not optional while you arrange testing and treatment.

Frequently Asked Questions

What does giardia poop look like? Giardia stool is classically loose or watery, greasy or oily, and unusually foul-smelling, and it often floats rather than sinks. The greasiness comes from the parasite interfering with fat absorption in the small intestine. Stools are not typically bloody; blood in the stool points toward a different cause and should be evaluated by a clinician.

How long does giardia last? Symptoms usually begin one to two weeks after infection and last two to six weeks. Some people develop long-term symptoms that can persist for months or years if untreated. Prescription treatment shortens the illness considerably, and many people improve within days of starting the right medication.

Is giardia contagious? Yes. Giardia spreads from person to person through the fecal-oral route, and swallowing just a few cysts can cause infection. It passes easily in households, childcare settings, and through sexual contact involving exposure to stool. People without symptoms can still carry and spread the parasite, so handwashing matters even after you feel better.

How do you get giardia while traveling? Most commonly by swallowing contaminated water from springs, lakes, rivers, or shallow wells, or by gulping recreational water while swimming. You can also get it from food washed in contaminated water, from an infected food handler, or from contaminated hands and surfaces. Backcountry trekkers and travelers in areas with limited safe drinking water are at highest risk.

What is the best medication for giardia? The commonly used prescription options are tinidazole, metronidazole, and nitazoxanide. Tinidazole is often preferred because it can be given as a single dose and tends to be better tolerated than metronidazole. Nitazoxanide comes as a liquid, which is helpful for children. A clinician chooses based on your age, pregnancy status, and other medications. There is no effective over-the-counter cure.

Can giardia go away on its own? Sometimes the immune system clears a mild infection, but giardiasis commonly lasts weeks and can become chronic, with ongoing diarrhea, malabsorption, and weight loss. Because prescription treatment is short and effective, most clinicians recommend treating confirmed giardia rather than waiting it out.

Does boiling water kill giardia? Yes. Bringing water to a rolling boil for at least 1 minute (3 minutes at elevations above 6,500 feet) reliably kills giardia cysts. Filtration with a filter rated to 1 micron or smaller also works. Chlorine and iodine tablets are less reliable against giardia cysts, so use them only as a backup when boiling or filtering is not possible.

Why do I still feel sick after giardia treatment? Some people develop temporary lactose intolerance after a giardia infection, so dairy can trigger bloating and loose stools for a few weeks even after the parasite is gone. This usually resolves on its own. If significant symptoms persist after treatment, contact your clinician, since occasionally a second course or a different medication is needed.

Medical Disclaimer

This article is for general educational purposes and does not replace personalized medical advice. If you have prolonged diarrhea, signs of significant dehydration, blood in your stool, or a high fever, seek medical care. Always consult a licensed clinician about your specific health conditions, medications, and travel plans before starting any treatment.

Sources

• CDC, "About Giardia Infection" (May 2024). https://www.cdc.gov/giardia/about/index.html
• CDC, "Giardia Infection Prevention and Control." https://www.cdc.gov/giardia/prevention/index.html
• CDC, "Treatment of Giardia Infection." https://www.cdc.gov/giardia/treatment/index.html
• CDC Yellow Book, "Giardiasis," Travelers' Health. https://wwwnc.cdc.gov/travel/yellowbook/2020/travel-related-infectious-diseases/giardiasis
• CDC Yellow Book, "Travelers' Diarrhea." https://www.cdc.gov/yellow-book/hcp/preparing-international-travelers/travelers-diarrhea.html
• CDC, "Making Water Safe While Hiking, Camping, and Traveling." https://www.cdc.gov/drinking-water/prevention/water-treatment-hiking-camping-traveling.html
• Mayo Clinic, "Giardia infection (giardiasis): Symptoms and causes." https://www.mayoclinic.org/diseases-conditions/giardia-infection/symptoms-causes/syc-20372786
• Merck Manual Professional Edition, "Giardiasis." https://www.merckmanuals.com/professional/infectious-diseases/intestinal-protozoa-and-microsporidia/giardiasis