An upset stomach is among the most common illnesses people bring home from a trip abroad. A review of gut illness in returning travellers found that diarrhoea affects somewhere between 40% and 60% of international travellers, and that most cases are bacterial, short-lived and settle on their own within a few days. Diarrhoea is rarely the whole story either. The same review lists stomach pain, bloating and fatigue as common companions on the flight home.
The rest of this guide covers what lowers the risk while you are away, and when to worry once you are home. The short version is to take care with water, ice and uncooked food on the trip, and to see your GP if your gut has not settled within two weeks of getting back. Tell them where you travelled, because it changes what they look for.
Why do the first two weeks matter?
Doctors treat two weeks as a genuine dividing line, not a rule of thumb. A clinical review in JAMA, one of the world's leading medical journals, defines diarrhoea as persistent once it has lasted 14 days or more, and makes the point that the likely causes change at that point.
Short-lived diarrhoea is usually the work of bacteria or viruses, which your immune system clears quickly. Parasites are slower burners. They cause infections such as giardiasis that can grind on for weeks, so once diarrhoea passes the 14-day mark, parasites move to the top of the suspect list.
The same review estimates that around 3% of people travelling to lower-income countries develop persistent diarrhoea of this kind. That is a small share of all travellers, but a meaningful number of people every summer, and most of them start out assuming it is just a stomach bug that will not quite go.
There is a caveat about testing worth knowing early. Modern laboratory panels can look for many organisms in one sample, and the review of returning travellers notes that finding an organism is not always the same as finding the cause of your symptoms. That is why the results belong in front of a clinician who knows your history, not interpreted alone at home.
Which infections do UK travellers actually bring home?
The UK has an unusually well-documented answer, because its public health agencies investigate and publish what returning travellers bring back.
The clearest example is Cyclospora, a parasite spread through contaminated food and water. In the summer of 2015, Public Health England and Health Protection Scotland investigated 176 confirmed Cyclospora cases in travellers returning from the Riviera Maya region of Mexico, 79 of them in the UK. The pattern repeated in 2016 and again in 2017, with 78 UK cases reported by late July that year, mostly in people who had stayed in holiday resorts in the same region.
Cyclospora is a genuine travel specialist. Worldwide surveys pooling more than 166,000 tested people found that about 3.4% carried the parasite, but only 0.4% in high-income countries, so in the UK it is almost entirely something you bring home rather than something you catch here. It spreads through contaminated fresh produce and water rather than from person to person, because the parasite needs days to weeks outside the body before it becomes infectious.
It is an awkward one to have, too. The same US Food and Drug Administration review notes that the illness usually clears on its own in healthy people but can drag on or relapse, with symptoms fading and then returning. And the usual anti-parasite medicines do not work against it; the antibiotic that does needs a prescription, which is one more reason a laboratory diagnosis matters. Our guide to Cyclospora infection covers the symptoms and testing in detail.
Cryptosporidium tells a similar story. When England and Wales recorded their biggest jump in cases in autumn 2023, the UK Health Security Agency and Public Health Wales compared 203 affected people with 614 people who had a different gut infection. Those with cryptosporidiosis were around five times more likely to have used a swimming pool and around six times more likely to have travelled to Spain, with children under five the most affected group. No single cause explained the surge, but foreign travel was clearly part of it.
If your symptoms are dragging on after a trip, see your GP first and tell them where you went. A home screening test for gut parasites can also check a stool sample for Giardia, Cryptosporidium and other common culprits, and it works alongside your GP's assessment rather than instead of it.
Where is the risk highest?
The risk is not spread evenly. The review of returning travellers cited above reports travellers' diarrhoea most often in lower-income countries and least often in Europe and North America, a gap that tracks water and food sanitation. The areas that stand out are:
- Sub-Saharan Africa, with the highest reported rates of travellers' diarrhoea, affecting between roughly two and nearly nine in ten visitors across studies
- South Asia and parts of Southeast Asia, where reported rates reach about eight in ten in some studies
- Central and South America and the Caribbean, at lower but still substantial rates, including the Riviera Maya region of Mexico, the source of the UK's recurring early-summer Cyclospora waves between 2015 and 2017
- Spain, on one specific count, because travel there was among the strongest associations in the autumn 2023 Cryptosporidium surge in England and Wales
- Anywhere with limited drinking water sanitation. Worldwide, about 3.4% of tested people carried Cyclospora, but only 0.4% in high-income countries
Where you are going changes the risk more than anything you pack. TravelHealthPro, the UK's official travel health service, publishes food and water advice for each destination, and the UK Health Security Agency publishes specific advice for travellers on Cyclospora. Check your destination before you go.
How can you lower the risk while you are away?
The classic advice holds because the classic routes have not changed. In higher-risk destinations, drink bottled, boiled or filtered water, and skip ice unless you know it was made from safe water.
Food needs slightly more thought than water, because salads are the awkward case. Freshly cooked food served hot is the safest choice, and fruit you peel yourself is safer than fruit washed in local water. Salad leaves, fresh herbs and berries are the classic vehicles for Cyclospora, and in a resort you cannot see how they were washed, so it is reasonable to be choosy about raw produce in the regions with a track record.
Two smaller habits earn their place. Try not to swallow water when swimming, in pools or anywhere else, and wash your hands with soap and water before you eat, especially after using the toilet.
Timing plays a part as well. Cyclosporiasis is markedly seasonal, and the UK's Mexico-linked waves arrived in early summer each year, so the same destination can carry different risks in different months.
Prevention has a bigger picture too, because travel multiplies risks that exist at home rather than inventing new ones. Our guide to how gut parasites spread covers every route in more detail, at home as well as abroad.
None of this reduces the risk to zero. The travellers in the 2015-2017 Cyclospora waves were staying in resort hotels and doing nothing unusual. Careful habits shorten the odds; they do not remove them.
What should you do when you get home?
Usually, nothing. If you have a short-lived stomach upset, the NHS advice is fluids, rest, staying off work or school until you have been clear of symptoms for 48 hours, and staying out of swimming pools for at least 48 hours after they stop. Those 48-hour rules are about protecting other people, because several of these infections pass on easily while your gut is still recovering.
The calendar is the thing to keep an eye on. If your gut is still not right two weeks after you get back, book a GP appointment and mention the trip, including the countries and the dates. Travel history genuinely changes what happens next, because laboratories test a stool sample for different organisms depending on where you have been.
The first step is usually simple. Your GP can send a stool sample to an NHS laboratory free of charge, and the result shapes everything that follows, from treatment to how long you stay away from work.
It is also worth knowing what you might be dealing with. Our guide to the parasites that cause gut infections walks through each organism, what it does and how it is found.
When should you see a GP?
The NHS advises calling 111 or asking for an urgent appointment if you have had diarrhoea for more than 7 days, if there is blood in your diarrhoea, or if you cannot keep fluids down or have signs of dehydration, such as dark pee or peeing less than usual.
See your GP as well if you have unexplained weight loss, persistent vomiting, a fever that does not settle, or any change in your bowel habit that lasts more than three weeks, whatever the cause turns out to be. If your immune system is weakened by an illness or a treatment, seek advice early rather than waiting, because some gut infections are harder to shake off and can become serious.
Whenever you speak to a GP or 111 about gut symptoms, mention any travel in the past few months, even if the trip felt uneventful. Some infections take weeks to show themselves, and the connection is easy to miss.
This guide is for information only and does not replace medical advice. No home test diagnoses an infection, and none of the above is a reason to delay seeing a doctor.
Sources
- DuPont HL (2016). Persistent diarrhea: a clinical review. JAMA. PubMed | DOI
- Butler D, et al. (2022). Travel-related gastrointestinal diseases: assessment and management. Public Health Challenges. PubMed | DOI
- Nichols GL, et al. (2015). Cyclospora infection linked to travel to Mexico, June to September 2015. Eurosurveillance. PubMed | DOI
- Marques DFP, et al. (2017). Cyclosporiasis in travellers returning to the United Kingdom from Mexico in summer 2017. Eurosurveillance. PubMed | DOI
- Giangaspero A, Gasser RB (2019). Human cyclosporiasis. The Lancet Infectious Diseases. PubMed | DOI
- Almeria S, et al. (2019). Cyclospora cayetanensis and cyclosporiasis: an update. Microorganisms. PubMed | DOI
- Chen Y, et al. (2024). The global prevalence of Cyclospora cayetanensis infection: a systematic review, meta-analysis, and meta-regression. Acta Tropica. PubMed | DOI
- Williams SV, et al. (2025). Retrospective case-case study investigation of a significant increase in Cryptosporidium spp. in England and Wales, August to September 2023. Eurosurveillance. PubMed | DOI
- NHS. Diarrhoea and vomiting. nhs.uk
- UK Health Security Agency. Cyclospora: advice for travellers. GOV.UK
- TravelHealthPro (NaTHNaC). Destination-specific food and water advice. travelhealthpro.org.uk
