Specialty Testing Guide › GI-MAP Gut Testing
Most stomach trouble after travel is caused by bacteria or viruses and clears up within a week. Parasites are a less common cause overall, but they become much more likely when diarrhea, gas or cramping lasts longer than two weeks after you get home.
If your symptoms have dragged on, the right next step is a visit to your doctor for standard stool testing, not a home remedy. This guide covers the common culprits, how they are tested and when to get seen quickly.
Key takeaways
- Travelers' diarrhea is very common and is mostly bacterial, so it usually passes in days.
- Gut symptoms that persist beyond two weeks raise the odds of a parasite, with Giardia the most frequent.
- Standard testing includes ova-and-parasite checks on several samples, antigen tests and DNA-based panels, along with a C. diff test.
- Sometimes a trip infection is followed by IBS or uncovers celiac disease or inflammatory bowel disease, even after the bug is gone.
How common gut infections are after travel
Travelers' diarrhea is very common. Depending on the destination and season, 30% to 70% of travelers get it during a two-week trip.1
Bacteria cause most cases, an estimated 75% to 90% or more. Protozoa, the single-celled parasites, account for about 10% of diagnoses, mostly in people who travel for longer periods. Untreated bacterial diarrhea usually lasts three to seven days, while protozoal diarrhea can persist for weeks to months without treatment.1
Parasites to know about
- Giardia: the most common parasitic cause of persistent travelers' diarrhea. It often causes gas, greasy floating stools, cramps, nausea and tiredness.
- Cryptosporidium and Cyclospora: spread through contaminated water and food, and found with antigen tests or DNA panels.
- Entamoeba histolytica: a less common cause that standard DNA panels also look for.
- Blastocystis: often found in stool. Whether it causes illness is still debated, because it shows up in people with and without symptoms.2
You do not need to cross an ocean to meet Giardia. You can catch it from untreated water from springs, lakes, rivers or shallow wells, which is worth remembering if you camp, hike or drink from a private well here in Pennsylvania. Giardia symptoms usually begin one to two weeks after infection and last two to six weeks.3
When symptoms last more than two weeks
Doctors call diarrhea that lasts longer than 14 days persistent. As a group, parasites are the organisms most likely to be found in travelers with persistent diarrhea.4
Ongoing infection is only one possibility. A trip infection can also unmask a condition you already had, such as celiac disease or inflammatory bowel disease. And some people develop IBS symptoms after a bout of gastroenteritis, called post-infectious IBS, even when tests for germs come back clear.
How doctors test for parasites
Your doctor has several standard tools, and often uses more than one:
- Ova and parasite (O&P) microscopy: a lab looks at your stool under a microscope. When parasites are suspected, checking several samples collected over three or more days is appropriate, because a single sample can miss them.
- Antigen tests: detect proteins from specific parasites such as Giardia and Cryptosporidium.
- Multiplex PCR panels: detect the DNA of many organisms from one stool sample at once.
- C. diff testing: the first workup of persistent travelers' diarrhea should always include a C. difficile test, especially if you took antibiotics on your trip.
DNA panels are sensitive, which is a strength and a limitation. Molecular tests can detect organisms that are simply colonizing the gut rather than causing infection, so a positive result has to be matched to your symptoms.4 The same caution applies to broader DNA stool panels such as the GI-MAP, which our parasites on a stool test guide covers in detail.
When to see a doctor quickly
- Blood in your stool or black stools
- A high fever
- Signs of dehydration, such as very little urine, dizziness or a dry mouth
- Severe belly pain
- Diarrhea that lasts more than two weeks
- A weakened immune system, pregnancy or older age, which raise the stakes of any gut infection
Tell your doctor exactly where you went, what you ate and drank, and whether you took any antibiotics. That history guides which tests to order first. If you have severe symptoms or signs of serious dehydration, call 911 or go to an emergency department.
Your next step
For new symptoms after a trip, start with your primary care doctor or a travel medicine clinic, which can order standard stool tests quickly. If those come back clear and symptoms continue, you may want to understand what a broader panel can and cannot add. Read how DNA stool testing works, or browse the gut testing hub.
Frequently asked questions
Can a parasite stay in my body for years?
Some can. Occasionally, people with Giardia have long-term symptoms that can last for years.3 That is why persistent symptoms deserve testing rather than guessing.
Should I take an over-the-counter parasite cleanse?
No. Cleanse products are not a substitute for diagnosis, and the parasites that matter are treated with specific prescription medicines chosen after testing.
Why did my test come back negative if I still feel sick?
A single stool sample can miss parasites, which is why several samples are often checked. Your symptoms may also come from post-infectious IBS or another condition the trip uncovered, which is worth a follow-up visit.
Do I need treatment if Blastocystis shows up?
Not automatically. Because it is found in people without symptoms as well as people with them, a clinician weighs your symptoms and other results before deciding whether treatment makes sense.
Related reading
This article is for general education and is not medical advice. Decisions about testing and treatment should be made with your clinician. If you have severe symptoms, call 911. For a suspected poisoning, call Poison Control at 1-800-222-1222.
