Giardia at a glance
- What it is: a microscopic intestinal parasite that can cause diarrhea.
- Common symptoms: diarrhea, gas, cramps, nausea and fatigue; some people have none.
- Testing: a clinician can arrange stool testing. Symptoms or stool appearance alone cannot identify it.
- After treatment: symptoms can persist even after the infection clears.
What is Giardia?
Giardia duodenalis is a parasite that lives in the gut. The infection it causes is called giardiasis, sometimes nicknamed “beaver fever.” It occurs across the United States, and you do not need to travel abroad or encounter a beaver to get it. Infection can interfere with nutrient absorption and cause dehydration through diarrhea. CDC: Giardia overview.
Giardia symptoms in humans
Diarrhea is the most common symptom. Other symptoms include gas, cramps, nausea, tiredness and greasy, foul-smelling stool that may float. Some people have no symptoms. Symptoms usually begin 1–2 weeks after infection and last 2–6 weeks, although the course varies. Weight loss or prolonged diarrhea needs medical attention. CDC: symptoms and timing.
These symptoms overlap with other infections and digestive conditions. For example, floating stool after a camping trip is a reason to discuss exposure and testing, rather than assume Giardia from its appearance.
How do you get Giardia?
Infection begins when you swallow the parasite from something contaminated with feces. Possible exposures include untreated water, swallowed swimming water, food, hands or surfaces. It can also spread between people, including in childcare and through sexual contact involving fecal exposure. How Giardia spreads.
Reducing exposure and reinfection
- Wash hands with soap and water after using the toilet or changing diapers, and before handling food.
- Avoid swallowing swimming water; stay out of pools while you have diarrhea.
- Make wilderness water safe before drinking. CDC advises boiling for 1 minute, or 3 minutes above 6,500 feet.
- Clean and disinfect areas contaminated by diarrhea, following product directions.
See CDC prevention guidance for water filtration, childcare and sexual-contact precautions.
How is Giardia diagnosed?
A healthcare provider considers symptoms, exposure and stool-test findings together. CDC recommends three stool samples collected over several days for accurate results because shedding can vary. Follow the collection instructions for the specific test ordered; do not put several days of samples into one kit unless instructed. Why more than one sample may be needed.
- Direct fluorescent antibody (DFA) microscopy: CDC identifies this as the diagnostic gold standard.
- Antigen tests: look for Giardia proteins in stool.
- PCR-based tests: look for genetic material. Some test for Giardia alone; others include multiple organisms.
Discuss which option fits your symptoms and history with your clinician. A broader panel is not automatically the better choice for a specific suspected infection. CDC testing guidance · Overview of parasite testing.
What does Giardia on a GI-MAP result mean?
Giardia is one of the targets on the GI-MAP™ Standard. The laboratory uses qPCR to detect microbial DNA in a stool sample. This identifies a target in that sample; the number is not a direct measurement of intestinal damage or symptom severity. Laboratory methodology and targets (PDF).
- Detected: bring the complete report to a licensed clinician. A DNA finding needs clinical interpretation, especially after treatment; DNA detection does not necessarily establish that organisms are alive.
- Not detected: the target was not found above the assay’s detection limit in that sample. Persistent symptoms can still require further evaluation.
- A numerical result: do not use it alone to choose a drug, judge how ill you are or decide whether treatment worked.
These limits follow the distinction between detecting genetic material and diagnosing its clinical significance described in IDSA infectious-diarrhea guidance. GI-MAP does not replace assessment of acute diarrhea, and a single broad-panel result cannot establish the cause of every symptom.
Treatment and symptoms that persist
A clinician may prescribe medication and advise on hydration. CDC lists tinidazole, nitazoxanide and metronidazole among effective medicines. The choice depends on individual circumstances, including pregnancy and medical history; this guide does not recommend a personal treatment regimen. CDC patient-care guidance.
If symptoms continue, a clinician may check for ongoing infection, reinfection or a problem completing treatment. Symptoms can also last for weeks or months after the parasite has cleared. Do not assume persistent bloating means you need another course of medication or another broad stool panel.
Research describes postinfectious irritable bowel syndrome (IBS), fatigue and food intolerance after giardiasis. These are possible outcomes, not a prediction for every patient. A GI-MAP result alone cannot diagnose postinfectious IBS or prove that a recovery plan is working. CDC review of longer-term effects.
Frequently asked questions
Can Giardia cause a fever?
Yes. CDC lists fever as a less common symptom. Its presence or absence cannot confirm or exclude Giardia; many illnesses cause diarrhea and fever.
What does Giardia poop look like?
Stool may be greasy, unusually smelly or floating, but appearance alone cannot identify Giardia. Laboratory testing is needed to investigate a suspected infection.
Is Giardia the same as giardiasis?
Giardia is the parasite; giardiasis is the infection it causes. Giardia duodenalis, Giardia intestinalis and Giardia lamblia are names used for the same organism. “Beaver fever” is an informal name for giardiasis.
Do I need another test after treatment?
CDC recommends retesting only when symptoms continue after treatment. Your clinician chooses the test and timing. Persistent symptoms do not automatically mean the parasite is still present.
Sources: the linked CDC, NIDDK and IDSA resources support the health information above. Diagnostic Solutions Laboratory documents the assay’s targets and method; its guide is not independent evidence that buying or repeating GI-MAP improves recovery. Sources checked 10 October 2026.