IBS After Food Poisoning: What the Cohorts Show

Yes, food poisoning can cause IBS. It has a name, post-infectious IBS, and it is one of the few ways IBS starts that researchers can actually date to a single event. Across dozens of follow-up studies, somewhere between one in ten and one in seven people who get gastroenteritis go on to meet the criteria for IBS (Klem 2017, Porcari 2024). The risk is higher after parasites and bacteria than after viruses, and higher in people whose original illness was severe.

The question most people are really asking, though, is the one in the title of a 145-comment r/ibs thread: is there anyone who actually recovered? That is where most pages on this topic go vague, and where the research is more useful than its reputation. Several cohorts have followed people for six, eight and ten years. Their answers differ by bug, and the "it takes eight years" figure that circulates in patient forums turns out to be the length of one study's follow-up, not a recovery time. This article lays the cohorts side by side, sorts out what your timeline means, and covers what else can start after a bout of food poisoning.

If you are only a week or two out, start with the section on your timeline. Some of what follows does not apply yet.

The short answer: yes, and it has a name

Post-infectious IBS (often shortened to PI-IBS) is IBS that begins straight after an episode of infectious gastroenteritis in someone who did not have IBS before. The infection clears, but the bowel does not go back to how it was. People most often describe ongoing loose or urgent stools, cramping, bloating and a gut that suddenly reacts to foods it used to handle.

The Rome Foundation, the body that writes the diagnostic criteria for IBS, convened a working team on it. Their report states that PI-IBS develops in about one in ten people with infectious enteritis and calls acute gastroenteritis one of the strongest known risk factors for IBS. It also makes a point worth holding onto if you have been told this is "just IBS": the fact that new cases can be traced to a dated, objective event like an infection undercuts the old idea that IBS comes from nowhere (Barbara 2019).

That is also the theme of the 125-comment r/ibs thread that sits behind this keyword. Someone two months out from a restaurant meal, with a clear CT scan, a clear stool test and no answers, asks whether food poisoning can do this. The replies are a wall of people saying the same thing happened to them, some recently and some nine, twelve or twenty-four years ago. That spread of timelines is exactly what the research shows too, and it is why the useful question is not "can it happen" but "what decides how long it lasts".

How common is it? The numbers, bug by bug

Between roughly 10% and 15% of people who get gastroenteritis go on to develop IBS, depending on which pooled estimate you use and how long after the infection it was measured. The individual outbreak studies range far wider than that, from a few percent to over 40%, and the spread is informative rather than noise.

The two large meta-analyses give the anchor figures. One pooled 45 studies covering 21,421 people with enteritis followed for three months to ten years, and found IBS in 10.1% at 12 months and 14.5% at more than 12 months. Risk was 4.2 times higher than in people without enteritis during the first year, and 2.3 times higher after that. Of people whose infection was caused by protozoa or parasites, 41.9% developed IBS, against 13.8% after bacterial infection (Klem 2017). The later one pooled 47 studies with 28,170 people and found PI-IBS in 14.5% overall, with 4.3 times the odds of unexposed controls. Campylobacter had the highest prevalence among the individual bacteria with enough data, at 20.7% (Porcari 2024).

A few things are worth knowing before you read too much into any single row. The norovirus study was small: 139 of 197 conference delegates returned the first survey, 95% of them women, and the odds ratio at three months was 6.9 with a confidence interval running from 1.0 to 48.7, which is wide enough to say "probably more" and not much else (Marshall 2007). The parasite figure in the 2024 meta-analysis rests on only two studies, as its authors say. And the COVID-19 study recruited people sick enough to be admitted to hospital, so it tells you little about a mild infection at home (Marasco 2023).

Two weeks, two months, six months: what your timeline means

How long you have been unwell changes what your symptoms can be called, which tests make sense, and how much of the research applies to you. People in the threads often arrive at "post-infectious IBS" at two or three weeks, but formally the label cannot apply until month six.

The first week or so. US infectious disease guidelines define acute diarrhoea as lasting under seven days, and "prolonged" diarrhoea as lasting 7 to 13 days (Shane 2017). This is still the illness itself for most people, and the priorities are fluids and watching for warning signs.

Two to four weeks. Diarrhoea lasting 14 to 29 days is called persistent. This is where the same guideline shifts its attention. For travellers with diarrhoea lasting 14 days or longer, it recommends evaluation for intestinal parasites, C. difficile testing if they took antibiotics in the previous 8 to 12 weeks, and considering IBD and post-infectious IBS. More generally, it says C. difficile testing may be considered in anyone whose diarrhoea followed antibiotic use, or whose persistent diarrhoea has no identified cause (Shane 2017). It also recommends considering non-infectious causes, including IBD and IBS, in anyone whose symptoms have lasted 14 or more days without an identified source. The r/ibs thread from someone three weeks out after a stomach bug, with diarrhoea several times a day and exhausting bloating, sits exactly here. One of the replies asks the right question: has anyone tested for C. difficile?

One to six months. Diarrhoea lasting 30 days or more is chronic (Shane 2017). You may well be on the road to post-infectious IBS, and your doctor may use the phrase. But the Rome Foundation working team's criteria require recurrent abdominal pain on average at least one day a week over the last three months, with symptom onset at least six months before diagnosis, starting immediately after the infection has resolved, in someone who did not meet IBS criteria before (Barbara 2019). Before that, it is a working description, not a diagnosis.

Six months on. This is when the formal label can apply, and when most of the long-term research becomes relevant to you. It is also the point at which the norovirus cohort found the difference between people who had been ill and people who had not had disappeared (Marshall 2007), which is a reminder that a meaningful share of early cases do not reach this stage.

The criteria also define what counts as the infection. Ideally it is confirmed by stool culture or a validated molecular test, but because most people are never tested, the working team accepts two or more of fever, vomiting or diarrhoea during the acute illness (Barbara 2019). If you never had a stool test, that does not rule you out. In a large internet survey of people who met the criteria, only 24% reported a positive stool culture (Card 2018).

Is it still the infection?

Usually not, by the time weeks have passed, but this is the one possibility worth actively excluding, because it changes what happens next. The main candidates are parasites that outlast a bacterial or viral illness, and C. difficile, which can follow antibiotic treatment.

The infectious disease guideline names both: parasite testing for persistent diarrhoea after travel, and C. difficile testing as something to consider when diarrhoea follows antibiotic use (Shane 2017). One reply in the three-week thread describes being treated as if it were C. difficile without improvement and then waiting months for a colonoscopy, which is a reminder that ongoing severe diarrhoea deserves medical follow-up rather than waiting it out.

Two things in the same guideline help with a common source of confusion. First, it says multi-pathogen PCR panels detect DNA, not necessarily viable organisms, and that results need clinical interpretation (Shane 2017). So a positive result weeks later does not prove the bug is still active, which is relevant to the worry in one thread about norovirus "living" in the gut for months. Second, it does not recommend routine follow-up stool testing once diarrhoea has resolved. If your bowels are still not right, the reason to retest is that symptoms persist or new ones appear, not to confirm a cure.

What else can start after food poisoning

Post-infectious IBS is the most common explanation for gut symptoms that persist after an infection, but it is not the only one, and some of the alternatives have their own tests and treatments. These are the main ones the research links to an infectious start.

Inflammatory bowel disease. A UK primary care database study followed 43,013 adults after an episode of gastroenteritis and 50,000 matched controls for an average of 3.5 years. IBD was diagnosed at 68.4 per 100,000 person-years after gastroenteritis against 29.7 in controls, a hazard ratio of 2.4. The excess was greatest in the first year (hazard ratio 4.1), and the rise was larger for Crohn's disease than for ulcerative colitis (García Rodríguez 2006). The authors described their result as compatible with infection playing a role in starting or worsening IBD; a database study like this cannot separate a trigger from disease that was already beginning. In absolute terms the difference is about 39 extra cases per 100,000 person-years, roughly one extra case for every 2,600 person-years of follow-up, so it is uncommon. It is why blood in the stool, weight loss and night-time symptoms after an infection should not be put down to IBS without checking. Our guide to telling a Crohn's flare from a stomach bug covers the overlap from the other side.

Bile acid diarrhoea. In a series of 84 people whose SeHCAT scans showed bile acid malabsorption, 29 had no obvious cause, and 16 of those 29 gave a clear history of acute gastroenteritis before chronic diarrhoea began (Niaz 1997). A later retrospective series of 25 people with post-infective bile acid malabsorption found that most of those contacted were still on treatment years afterwards, which the authors took as a sign that the condition can be long-lasting (Menon 2011). Both are small single-centre series. The point is not that bile acids explain most post-infectious diarrhoea, but that this is a distinct, testable condition that can look exactly like IBS-D. Our bile acid malabsorption vs IBS guide covers the tests.

Microscopic colitis. The British Society of Gastroenterology lists features that should make a clinician think of microscopic colitis in someone with diarrhoea: female sex, age 50 or over, coexisting autoimmune disease, night-time or severe watery diarrhoea, diarrhoea for less than 12 months, weight loss, and medicines such as NSAIDs, proton pump inhibitors, SSRIs or statins (Vasant 2021). Several of those can describe someone a few months after food poisoning, which is why the question comes up in the threads. It needs a colonoscopy with biopsies to diagnose, and our type 7 stool guide covers how it presents.

Coeliac disease. British guidance recommends coeliac serology for everyone presenting with IBS-type symptoms for the first time, because abnormal coeliac tests are almost three times more common in people with suspected IBS than in people without symptoms (Vasant 2021). The test only works while you are still eating gluten, so do not cut it out before you have been tested.

Small intestinal bacterial overgrowth. SIBO comes up in almost every post-infectious thread. The evidence and the testing problems are contested enough that we have a separate article on SIBO versus IBS, including who funded the work behind the breath test thresholds.

What changes in the gut after an infection

Post-infectious IBS is not imagined, and it is not only about stress. Biopsy studies show physical changes in the bowel lining that outlast the infection, and prospective studies show that a person's state of mind at the time of infection also predicts who develops it. Both are true at once.

The clearest early evidence came from serial rectal biopsies in 21 people after Campylobacter enteritis. Enteroendocrine cells, the hormone-producing cells in the gut lining that help regulate secretion and movement, were markedly increased at the start and still raised at six and twelve weeks. Gut permeability, measured with a sugar absorption test, was raised initially and at twelve weeks. Immune cells (T lymphocytes) in the lining were raised too. A year later, seven of the participants had further biopsies, five of them with persistent loose stools, and their counts were still significantly raised. Ten people with established post-dysenteric IBS showed the same pattern (Spiller 2000). The numbers are small, but they describe a bowel that is still behaving as if it were recovering long after the bug is gone.

The British IBS guideline summarises the wider picture: raised mast cell numbers are the most consistent tissue finding in IBS and are more common in IBS-D and post-infectious IBS, and there is strong evidence that bacterial, viral or parasitic infections can trigger IBS (Vasant 2021). The Rome Foundation's working team describes the mechanism as multifactorial, involving the gut microbiome, the lining, serotonin signalling and the immune system, while being clear that these mechanisms are incompletely understood (Barbara 2019).

The other half of the picture comes from a prospective study of 620 primary care patients with confirmed Campylobacter infection who filled in questionnaires at the time of infection. The 49 who went on to meet IBS criteria at both three and six months had reported higher perceived stress, anxiety, somatisation and more negative beliefs about illness at the start. They were also more likely to have kept going during the acute illness until forced to stop, and less likely to rest early on. Depression and perfectionism were not associated (Spence 2007). That last finding is an association, not a trial, so it does not prove that resting prevents IBS. But it fits the gut-brain model of IBS, and the British guideline recommends that the explanation of IBS given to patients includes postinfective changes alongside diet and stress (Vasant 2021). If stress is part of your picture, our article on stress and IBS flares covers the gut-brain side.

Who is more likely to develop it

The risk factors that recur across studies are the severity of the original illness, being a woman, being younger, and psychological distress before or during the infection. Antibiotic use during the illness is also linked to higher risk.

Two cautions apply. The antibiotic link is an association: people given antibiotics tend to be sicker, so the drug and the severity are hard to separate, and none of this is a reason to refuse antibiotics a clinician says you need. And the psychological factors describe risk across groups, not a judgement about why any one person got ill.

Does it go away? The recovery numbers, cohort by cohort

For many people, yes, symptoms ease or stop meeting IBS criteria over the following years. But how fast, and for what share of people, depends heavily on the infection and the person, and the studies disagree enough that any single number would be invented.

Here is what the long-term cohorts actually found.

Read across those rows and three patterns stand out.

The infection matters. After norovirus, the extra IBS cases had gone by six months. After a bacterial water outbreak, they shrank slowly over years. After Giardia, they barely moved between six and ten years. A virus-triggered case and a parasite-triggered case are not on the same clock.

"Recovery" usually means "no longer meets the criteria". Most of these studies count someone as recovered when they no longer meet Rome criteria. That can mean anything from no symptoms at all to milder symptoms that fall just below the threshold. The pooled finding that IBS persisted in 39.8% beyond five years (Porcari 2024) implies most people no longer met criteria by then, but it does not tell you how many feel completely normal.

Post-infectious IBS may or may not do better than other IBS. The Rome working team wrote that natural history studies suggest symptoms decrease over time and that the prognosis could be better than for IBS in general, but that this "is not substantiated by well-designed comparative studies" (Barbara 2019). The two head-to-head comparisons above, Nottingham and the internet survey, both found no significant difference, and both were small or had low follow-up. The honest position is that the better prognosis is plausible and unproven.

Within any cohort, some groups recovered more slowly. In the internet survey, 38.8% of men stopped meeting criteria in the first year against 20.7% of women; people with high somatic symptom scores and people living in North America or Northern Europe also did worse, and people whose IBS was more than three years old recovered less often (25%) than people whose IBS began within the past three years (38%), though that last difference fell short of statistical significance (Card 2018). In the Nottingham cohort, one of eight people with a history of anxiety or depression recovered, against nine of nineteen without, though with numbers this small the difference was not statistically significant (Neal 2002).

Where "it takes eight years" comes from

The idea that post-infectious IBS takes about eight years to resolve is everywhere in patient forums. In one thread, people trade it as a fact alongside "almost 50% eventually resolve". In another, someone describes being devastated by "the eight-year recovery estimate" a month into their diagnosis, then reports major improvement by month five. We could not find any study that reports an eight-year average recovery time.

The number almost certainly traces to the Walkerton cohort. Its title is "Eight year prognosis of postinfectious irritable bowel syndrome", because eight years is how long the researchers followed people. Its conclusion is that gastroenteritis "can trigger IBS symptoms that persist for at least 8 years" (Marshall 2010). That is a statement about the people who were still affected when the study stopped, not about how long it takes the average person to recover. Over that same period, the share of formerly ill residents who met IBS criteria roughly halved.

The other figure that circulates, "less than half recover over six years", is a direct quote from the Nottingham study's conclusion. It is accurate, but it rests on 14 people with post-infectious IBS, six of whom recovered (Neal 2002). A reply in the same thread made exactly this point: neither study is large enough to support confident predictions for any one person. The best summary we can give is that time helps many people, the pace varies widely, and nobody can honestly give you a date. If you also want to know how long individual bad patches last once IBS is established, our IBS flare duration guide explains why no reliable figure exists for that either.

What to eat while it is still going on

There is less evidence here than the confident advice online suggests. For the acute illness, guidelines favour going back to a normal diet early. For the weeks and months afterwards, we could not find a trial that tested any diet specifically in people recovering from food poisoning.

During and straight after the illness. The US infectious diarrhoea guideline recommends resuming a usual diet during or immediately after rehydration. It states that although the BRAT diet (bananas, rice, applesauce, toast) and avoiding dairy are commonly recommended, the supporting data for both are limited, and that telling people to stop eating solid food for 24 hours does not appear useful (Shane 2017). Fluids come first, especially if you have been vomiting or have had a lot of diarrhoea.

Dairy. Many people cut dairy after food poisoning on the theory that the infection has wiped out the lactase enzyme. That does happen after some viral infections in young children, but the adult evidence is thin and points the other way. In a prospective study of adults after culture-confirmed bacterial gastroenteritis, none of the 24 who developed post-infectious IBS or functional diarrhoea had an abnormal breath hydrogen result after a lactose load (four had a flat blood glucose response, but so did six of the 18 controls), and the authors concluded that advice to avoid dairy on the assumption of lactose intolerance appeared unnecessary in their population in northern England (Parry 2002). It was a small study, and the US guideline does list lactose intolerance as something to consider if diarrhoea persists (Shane 2017). If dairy seems to bother you, it is a reasonable thing to test, not a rule. Our piece on why lactose-free milk can still upset your stomach covers what else in dairy can be the culprit.

Once it has gone on for weeks. At this point the advice for IBS generally becomes relevant, because there is no separate evidence base for the post-infectious form. Many people in the threads describe eating as blandly as possible and finding that everything feels like a trigger. Some report that a low FODMAP trial helped, and others, like the person whose positive outcome thread described two weeks on it, found it made little difference. A low FODMAP diet is meant to be a short, structured process with a reintroduction phase, ideally with a dietitian, not a permanent way of eating. Our guide to what FODMAP stands for explains the groups, and the worst foods for IBS article covers which suspects hold up under blinded testing. The British guideline also advises avoiding insoluble fibre such as wheat bran, which can worsen symptoms (Vasant 2021).

Be wary of a shrinking safe list. Eating less to feel better carries its own nutritional cost, and restriction that starts during a bad patch has a way of outlasting it. If your diet has narrowed to a handful of foods, that is a reason to ask for a dietitian referral.

Blood tests that claim to prove it

There is no test that confirms post-infectious IBS. A blood test measuring antibodies to a bacterial toxin (anti-CdtB) and to a gut protein (anti-vinculin) is marketed as an IBS diagnostic and is often recommended in post-infectious threads, so it is worth knowing what the studies behind it show.

The idea is that some bacteria that cause food poisoning produce a toxin called CdtB, and that antibodies against it cross-react with vinculin in the gut wall. The development study recruited 2,375 people with IBS-D from a drug trial and compared them with people with IBD, people with coeliac disease and 43 healthy controls. For anti-CdtB, specificity was 91.6% but sensitivity was 43.7%. For anti-vinculin, specificity was 83.8% and sensitivity 32.6%. Both tests were less specific at telling IBS from coeliac disease (Pimentel 2015). A sensitivity of 43.7% means the test came back negative in more than half of the people with IBS-D. A negative result tells you very little.

The study's competing interests statement discloses that the test samples from the drug trial were analysed with funding from Salix Pharmaceuticals, that Salix paid the salaries of two authors, and that Cedars-Sinai had licensing agreements with Salix, Commonwealth Laboratories and Synthetic Biologics (Pimentel 2015). Our SIBO article sets out how those relationships connect to breath testing as well.

A later replication is the more striking result. A 2024 study of 160 people, with the test's developer among its co-authors, found anti-CdtB positive in 43.2% of people with IBS-D and in 45.7% of healthy controls, and anti-vinculin positive in 34.1% and 47.8% respectively. Its conclusion was that the antibodies "could not identify IBD-IBS patients or discriminate IBS-D from healthy controls" (Barros 2024).

There is also a design point that matters to anyone using the test to answer "did food poisoning cause my IBS?". The validation compared IBS-D against IBD and coeliac disease. It did not compare IBS that started after an infection with IBS that did not. So even a positive result does not tell you how your IBS began.

The same caution applies to IgG food intolerance tests, which some sellers market specifically for gut symptoms after food poisoning. The British Society of Gastroenterology recommends against elimination diets based on IgG antibody testing in IBS (Vasant 2021).

Should you push for more tests?

Push for the right tests, not for every test. The useful ones depend on how long you have been unwell, your age, your pattern, and whether any warning signs are present.

A reasonable baseline, drawing on British IBS guidance, is a full blood count, a marker of inflammation (CRP or ESR), coeliac serology, and, for people under 45 with diarrhoea, a faecal calprotectin to look for IBD (Vasant 2021). The infectious disease guidance adds stool testing for parasites when persistent diarrhoea follows travel, and considering C. difficile testing when diarrhoea follows antibiotics (Shane 2017). If the baseline is normal and there are no warning signs, the British guideline says other investigations should be kept to a minimum, and notes that the yield of colonoscopy in IBS is extremely low, with no evidence that a normal result reassures people. The exceptions it names are colonoscopy when microscopic colitis is suspected, and tests for bile acid diarrhoea in suspected IBS-D (Vasant 2021).

That fits what the first thread describes: CT clear, stool tests clear, colonoscopy clear the year before, and a wait of several months for a gastroenterologist. In that situation, the most useful thing is often not another scan but a clear record of what is happening, which the next section covers. If you are trying to decide whether a referral is worth it, our guide on whether to see a gastroenterologist for IBS walks through what a GP can do first. The British guideline also says that once IBS is diagnosed, a GP should aim to follow up within two months to check symptoms are not getting progressively worse (Vasant 2021).

What to record in the first six months

Because the diagnosis depends on dates and on details of the original illness, a few notes now can save a lot of guesswork later. Most of this cannot be reconstructed accurately from memory a year on.

The illness itself, written down once. The date it started. What you think caused it, and whether anyone else who ate the same food got ill. Whether you had fever, vomiting, or blood in your stool, since the diagnostic criteria use fever, vomiting and diarrhoea to define the infection (Barbara 2019), and severity markers like fever, weight loss and bloody stools appear repeatedly as risk factors. How many days the acute phase lasted. Any stool test result and organism. Any antibiotics, with dates.

Then a light daily record. Stool form on the Bristol scale, how many times you went, pain on a simple 0 to 10 scale, urgency, and anything unusual such as night-time waking to open your bowels or blood. Our guide to keeping an IBS food diary covers the mechanics, and if you would rather not use an app, the paper and spreadsheet route works just as well.

Look at the trend monthly, not daily. Recovery after infection is rarely a straight line, and the threads are full of people describing a good fortnight followed by three bad days. A weekly average of stool frequency or pain shows direction far better than any single day. If you want help spotting delayed food patterns and pulling the record into a one-page summary for an appointment, that is what Clairop is built for: it lets you log meals and symptoms in seconds and highlights possible delayed triggers. Our guide to symptom trackers for doctors covers what a clinician will actually read.

An illustrative timeline

To make the timeline concrete, here is how the guidance above maps onto a typical course. It is a composite built from the research and the patterns described in the threads, not a real person's history.

Day 0 to 5. Sudden diarrhoea and cramps after a meal out, with a fever on day one and vomiting overnight. Fluids, rest, and back to normal food as soon as it stays down, in line with the infectious disease guidance (Shane 2017). The acute phase settles by day five.

Week 2. Stools are still loose two or three times a day, with cramping after meals. This is now persistent diarrhoea by the US definition. A call to the GP leads to a stool sample, and because there was a course of antibiotics two months earlier for a chest infection, a C. difficile test as well. Both come back negative.

Month 2. Better than week two, but not right: urgency most mornings, bloating by the evening, and a feeling that bread and onions now set things off. Blood tests and coeliac serology are normal. A calprotectin is borderline, so the GP arranges a repeat rather than reading much into it, mindful that infection can raise it (Vasant 2021).

Month 6. The repeat calprotectin is normal. Pain is still there about two days a week and linked to bowel movements. With symptoms that began straight after a clear-cut infection, have lasted six months and meet the Rome criteria, the GP now uses the term post-infectious IBS (Barbara 2019), and a dietitian referral follows for a short, structured trial of a low FODMAP diet with reintroduction.

Month 12 onwards. This is where the cohorts diverge. If the infection had been norovirus, the research suggests most of the excess risk would already have faded. After a bacterial infection, slow improvement over years is the commonest pattern in the Walkerton data. Had any warning sign appeared at any point, the plan would have changed immediately.

Myths about IBS after food poisoning

"Post-infectious IBS takes eight years to go away." No study we found reports that. Eight years is the length of the Walkerton follow-up, during which the share of people with IBS roughly halved (Marshall 2010).

"It's permanent." For many people it is not. IBS persisted beyond five years in 39.8% of people in pooled studies (Porcari 2024), and after norovirus the excess was gone by six months (Marshall 2007). But for some, particularly after parasitic infection, it does last a long time (Litleskare 2018).

"Post-infectious IBS is the one kind that always clears up." A common hopeful line in the threads, and not supported. The Rome working team says a better prognosis than other IBS is plausible but unproven (Barbara 2019), and the two direct comparisons found no significant difference (Neal 2002, Card 2018).

"If your stool test was negative, it can't be post-infectious." Most people with this condition never had a positive culture. The criteria accept fever, vomiting or diarrhoea in the acute illness as evidence of infection (Barbara 2019), and only about a quarter of survey participants reported a positive culture (Card 2018).

"Food poisoning always leaves you lactose intolerant, so cut dairy." In adults after bacterial gastroenteritis, the one prospective breath test study found no persistent lactose intolerance (Parry 2002).

"A blood test can prove your IBS came from food poisoning." The antibody test was validated against IBD and coeliac disease, not against IBS that started some other way, misses more than half of people with IBS-D, and in one study did not separate IBS-D from healthy people (Pimentel 2015, Barros 2024).

"It's all in your head." Biopsies after Campylobacter show measurable changes in the gut lining lasting a year or more (Spiller 2000). Stress and anxiety at the time of infection raise the risk (Spence 2007), which is a gut-brain interaction, not an imaginary illness.

When to see a doctor promptly

Most persistent gut symptoms after food poisoning are not dangerous, but some patterns need prompt medical attention rather than waiting to see if they settle. See a doctor promptly, or seek urgent care if you feel very unwell, if you have:

• Blood in your stool, or black, tarry stools.
• Signs of dehydration: very little urine, dizziness on standing, confusion, or being unable to keep fluids down.
• A fever that persists or returns after the acute illness.
• Unexplained weight loss.
• Diarrhoea that wakes you from sleep.
• Diarrhoea after a recent course of antibiotics, given the C. difficile risk (Shane 2017).
• Symptoms starting after age 50, or a family history of bowel cancer, IBD or coeliac disease.
• Anaemia on a blood test.
• Diarrhoea lasting two weeks or more, which is the point at which guidance says to look for persistent infection and non-infectious causes (Shane 2017).

Severe or worsening abdominal pain, a swollen tender abdomen, or not passing stool or wind are reasons to seek urgent care the same day. If the worry itself is wearing you down, our article on IBS and health anxiety looks at how to tell a red flag from the fear of one.

The short version

Food poisoning can trigger IBS, and it does so in a meaningful minority of people, roughly 10% to 15% across the pooled studies and more after parasites and bacteria than viruses (Klem 2017, Porcari 2024). Formally, it is a six-month diagnosis, so weeks two to twenty-four are about excluding persistent infection and look-alikes, not about labels (Barbara 2019, Shane 2017). Many people improve over the following years, but how quickly depends on the bug and the person, and nobody can honestly give you a date. Keep a simple record, get the right tests rather than every test, avoid narrowing your diet more than you need to, and see a doctor promptly for any warning sign.