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Gut symptoms, fatigue, and what food poisoning can leave behind
By Pam Killeen
Picture a summer picnic. Several guests eat from the same bowl of potato salad. A few get sick. Before long, the worst seems to have passed, and everyone moves on, except perhaps one person, whose digestion never quite settles.
That’s what I want to explore. Not just why some people get sick after a contaminated meal, but why some of them are still not well a year later.
Three Outbreaks, One Problem
Almost weekly there’s another recall. Listeria in deli meat, Salmonella in onions, E. coli in leafy greens. The notices arrive so regularly that most of us skim past them.
The 2026 Cyclospora outbreak was harder to skim past. On September 11, the U.S. Centers for Disease Control and Prevention declared the iceberg lettuce outbreak over, reporting 12,883 illnesses across 21 states. The contaminated lettuce was no longer in stores or restaurants.1
An outbreak ending and a person recovering aren’t the same thing. The announcement told us the lettuce was gone. It didn’t tell us whether everyone who had been ill was feeling well again.
Humans are the only known host of Cyclospora cayetanensis, which tells you something about how it reached the lettuce. The contamination traces back to human waste reaching the produce, or the water used on it, somewhere along the chain.2
Walkerton, Ontario, offers another example. In May 2000, heavy rain washed manure from a nearby cattle farm into one of the town’s shallow wells. The organisms were E. coli O157:H7 and Campylobacter. At least seven people died and more than 2,300 fell ill, in what remains the worst public health disaster involving municipal water in Canadian history.3
Yuma, Arizona, is yet another example. In 2018, romaine lettuce from the region sickened 210 people in 36 states and killed five.4 Investigators concluded that irrigation canal water most likely contaminated the crop.5 The stretch of canal carrying the outbreak strain ran beside a feedlot that FDA said could hold more than 100,000 cattle,6 though investigators found no clear route from the feedlot to the water.5
Different organisms and different routes, but the same underlying problem: contamination of what people eat and drink.
Walkerton also tells us something about what came afterward, because residents were followed for years. Eight years on, people who had experienced acute gastroenteritis during the outbreak were more likely to have developed high blood pressure than those who hadn’t been ill or had only mild symptoms, and a small number had gone on to develop measurable kidney damage. The authors recommended follow-up checks of blood pressure and kidney function for anyone who has had this kind of infection.7
The published follow-up ran eight years. What came after that I know only from people. Over the years I’ve spoken with Walkerton residents, and with family members of residents, and several of them will tell you that some people there are still unwell more than twenty-six years on. That’s testimony rather than published data, and I’m offering it as testimony, not as evidence. Long-term follow-up is expensive, and it tends to stop long before the people in it do.
What Can Linger After Food Poisoning
It’s easy to think of food poisoning as a miserable few days followed by a return to normal. The research tells a more complicated story. A 2017 review of studies involving more than 21,000 people found that about one in ten had developed irritable bowel syndrome, or IBS, a year after an intestinal infection. Their risk was more than four times that of people who hadn’t had the infection.8
IBS involves recurring abdominal pain together with changes in bowel habits, such as diarrhea or constipation. But the effects of an infection aren’t always limited to digestion.
After a 2004 Giardia outbreak linked to contaminated drinking water in Bergen, Norway, researchers followed people who had been infected. Six years later, about 31 percent of those who responded reported chronic fatigue, compared with 11 percent of the group who hadn’t been infected. Bowel problems were also more common among those who had been infected.9
Joints can be affected too. Reactive arthritis is a recognized complication of several bacteria behind common food poisoning, including Campylobacter, Salmonella, Shigella, Yersinia and E. coli O157. Joint pain and swelling can begin weeks after the original illness.10
One outbreak can’t tell us what every organism will do or explain everyone’s symptoms. What stays with me is the length of time involved. The Bergen and Walkerton studies followed people for years, not just through the first weeks of illness.
Is the Infection Still There?
Before asking why recovery takes longer for some people, there’s an important distinction. Sometimes the original infection is still active. Untreated Cyclospora can cause symptoms that fade and return, and there’s a recommended antibiotic treatment that targets the parasite.11
In other cases, the infection has cleared, but bowel symptoms continue. When someone develops IBS afterward, it’s called post-infectious IBS, and those symptoms aren’t by themselves proof that a parasite is still present. The two situations may feel similar, but they need different assessment and treatment.11 That’s something to work through with a clinician rather than guess from a symptom list.
The Questions I Keep Coming Back To
As a health coach and author, I’m interested in both the infection and the person living through it. Two questions sit underneath that, and they’re easy to run together.
Why does an organism take hold in one person and not in another? And why do symptoms sometimes continue in someone long after that organism is gone?
Those are different questions and they may not share an answer. The second is the one that matters most to a person who’s still unwell two years later.
Start with what can be accounted for. People at the same meal may swallow different amounts of a contaminant, and the severity of that first illness is one of the things linked with a greater chance of lasting bowel problems.8 But the number of helpings someone ate can’t tell us why they recovered differently.
Two guests can eat the same amount and end up in different places. One is unwell for a week. The other is still not right a year later.
My own view, after being involved in the natural health industry for nearly forty years, is that the second person’s internal terrain was already weak. By internal terrain I mean the state of the body an organism arrives in, and how much resistance it meets when it gets there.
I cannot prove that from the studies above, and I will not pretend otherwise. Lasting symptoms aren’t evidence that a particular person was unwell before the infection. Whether the health someone brings to an infection shapes their recovery from it is still an open question. That isn’t a reason to stop asking it.
One detail in the research does interest me. Antibiotic use during an intestinal infection has been linked with later IBS. The link doesn’t prove the antibiotics caused anything, because people with more severe infections are more likely to be given them in the first place.8 But it’s worth knowing what antibiotics do.
They can disrupt the balance of microbes in the gut, the community of trillions of organisms collectively called the microbiome. That community isn’t a passive tenant. It helps break down food, produces compounds your cells use, and occupies space that would otherwise be available to something else.
That last part matters more than most people realize. Some gut microbes help keep particular pathogens from taking hold by competing for nutrients and producing substances that inhibit them. Researchers call this colonization resistance.12
So the internal ecosystem isn’t a background detail. It’s part of what decides whether an organism that reaches you takes hold at all. What it doesn’t explain is why symptoms sometimes continue long after an infection has cleared. That’s the second question, and it’s the harder one.
Whatever the answer turns out to be, I doubt it’s a fast one. Improving terrain takes time out of your day, week after week, which is part of why it gets less attention than a protocol does.
What I can describe is where I look when someone is still unwell and the organism is long gone, and that’s what the rest of this article is about. The fuller version is my book, Parasites & the Terrain.
What I Mean by Terrain
Terrain is the word I use for the larger picture, and the microbiome is one part of it. In my work that means asking about sleep, light exposure, food and minerals, stress, breathing, and digestion. How well is someone sleeping? What are they able to eat? What does an ordinary day demand of them when they already feel exhausted? These are the everyday questions that interest me.
None of this proves that working on those things treats post-infectious illness. But a study and a person are asking different questions. A study asks whether something helps on average. The person in front of me wants to know whether they’ll sleep better and hurt less than they did last month.
The second answer arrives one person at a time, and it can’t settle the first. It still matters to the person it happens to, which is why I think this work belongs alongside medical care rather than instead of it.
Terrain can sound like an accusation, so it’s worth being clear about what actually wears it down. Plenty of it is ordinary: broken sleep, a diet built around convenience, hours under artificial light and not many outdoors, training harder than you can recover from. Other things arrive uninvited, like a death in the family, a car accident or other trauma, a long stretch of caregiving, or a course of antibiotics that was genuinely needed at the time. None of it is a moral failing, and most of it’s just what life looks like.
If ordinary living is most of what wears terrain down, then ordinary living is most of what builds it back. Sleep can be repaired. Minerals can be balanced. Stress can be lowered even when it can’t be removed. The ground underneath can be better than it is now.
When the Tests Come Back Normal
There’s a particular kind of exhaustion that comes from being told you’re fine. Not once, but repeatedly. You feel terrible month after month, more bloodwork is drawn, and every result comes back within range. Your body says one thing and the paperwork says another, and the paperwork is the one everyone else can read. I spent years in that position.
Normal results are useful and can be reassuring, but they don’t rule out every explanation for persistent symptoms, and they need to be read alongside your symptoms and medical history.13
If this sounds familiar, tell your clinician when the symptoms began and whether an intestinal illness came first. Ask whether the original infection could still be present and whether targeted stool testing makes sense.14 Worth knowing: CDC says many U.S. laboratories don’t automatically test for Cyclospora even when testing for parasites, so depending on your symptoms and exposure it may need to be requested by name.15
Read a negative result carefully, though. Some infections can be missed on a single sample. CDC says Cyclospora in particular can be hard to detect. Even someone with symptoms may not pass enough of the parasite in a single sample for a test to find it, which is why specimens collected on different days are sometimes needed.15
A positive result can help guide the next steps. A single negative doesn’t always rule out an infection, though appropriate negative testing does make one less likely. Persistent symptoms can also have explanations other than an organism that’s still present.
Separately, tell your clinician promptly about unexplained weight loss or blood in your stool, rather than filing it under IBS.14
Back to the Picnic
The vomiting may have stopped. The person may have gone back to work. That doesn’t tell you how they felt months later. If you’ve been unwell for a long time, it’s worth asking when it began. You may remember the week. You may even remember the meal. That’s not a diagnosis, but it is a piece of your history worth sharing.
That question is a large part of why I wrote Parasites & the Terrain, due for publication on January 19, 2027. In the coming articles, I’ll look more closely at the everyday habits and conditions I explore in the book, from sleep and light exposure to nutrition and stress.
Getting through the worst symptoms is one milestone. Feeling well again is another.
Frequently Asked Questions
Can food poisoning cause long-term health problems?
For some people, yes. A 2017 review of studies involving more than 21,000 people found that about one in ten developed irritable bowel syndrome within a year of an intestinal infection. Other research has linked certain infections to lasting fatigue and joint pain. Most people recover fully, but not everyone does.
What is post-infectious IBS?
Post-infectious IBS is irritable bowel syndrome that develops after an intestinal infection such as food poisoning. It involves recurring abdominal pain and changes in bowel habits that continue after the original infection has cleared. Research suggests roughly one in ten people develop IBS within a year of an intestinal infection.
Why do I still feel sick weeks after food poisoning?
There are two broad possibilities. The original infection may still be active, which can cause symptoms that fade and return. Or the infection may have cleared while symptoms continue, as in post-infectious IBS. These need different assessment, so tell your clinician when your symptoms began and whether an illness came first.
Can food poisoning cause chronic fatigue?
It can in some cases. Six years after a 2004 Giardia outbreak in Bergen, Norway, about 31 percent of people who had been infected reported chronic fatigue, compared with 11 percent of those who hadn’t. That was one organism in one outbreak, so it can’t predict what will happen to any individual.
Can food poisoning cause joint pain?
Yes. Reactive arthritis is a recognized complication of several bacteria behind common food poisoning, including Campylobacter, Salmonella, Shigella, Yersinia and E. coli O157. It can cause joint pain and swelling that begin weeks after the original illness. If you develop new joint symptoms after a gut infection, mention the infection to your clinician.
Can a stool test miss an infection?
Yes. Some infections can be missed on a single sample. CDC notes that Cyclospora can be especially hard to detect, because someone with symptoms may not pass enough of the parasite for one test to find it. A negative result makes an ongoing infection less likely, but doesn’t always rule it out.
This article is for general information and is not medical advice. Please speak with a qualified healthcare provider about your own symptoms or before making changes to your care.
References
1. Centers for Disease Control and Prevention. Investigation update: Cyclospora outbreak, July 2026. Final update, September 11, 2026. Accessed September 20, 2026. Source
2. U.S. Food and Drug Administration. Cyclosporiasis and fresh produce. Accessed September 20, 2026. Source
3. Salvadori MI, Sontrop JM, Garg AX, Moist LM, Suri RS, Clark WF. Factors that led to the Walkerton tragedy. Kidney International. 2009;75:S33-S34. Source
4. Centers for Disease Control and Prevention. Multistate outbreak of E. coli O157:H7 infections linked to romaine lettuce. Final update, June 28, 2018. Accessed September 20, 2026. Source
5. U.S. Food and Drug Administration. Environmental assessment of factors potentially contributing to the contamination of romaine lettuce implicated in a multi-state outbreak of E. coli O157:H7. November 1, 2018. Accessed September 20, 2026. Source
6. FDA says cattle feedlot could be to blame for E. coli in canal water used on romaine. Food Safety News. August 7, 2018. Quotes FDA investigation update of August 6, 2018. Accessed September 20, 2026. Source
7. Clark WF, Sontrop JM, Macnab JJ, et al. Long term risk for hypertension, renal impairment, and cardiovascular disease after gastroenteritis from drinking water contaminated with Escherichia coli O157:H7: a prospective cohort study. British Medical Journal. 2010;341:c6020. doi:10.1136/bmj.c6020. Walkerton Health Study, eight-year follow-up. Source
8. Klem F, Wadhwa A, Prokop LJ, et al. Prevalence, risk factors, and outcomes of irritable bowel syndrome after infectious enteritis: a systematic review and meta-analysis. Gastroenterology. 2017;152(5):1042-1054.e1. doi:10.1053/j.gastro.2016.12.039. Source
9. Hanevik K, Wensaas KA, Rortveit G, Eide GE, Mørch K, Langeland N. Irritable bowel syndrome and chronic fatigue 6 years after Giardia infection: a controlled prospective cohort study. Clinical Infectious Diseases. 2014;59(10):1394-1400. doi:10.1093/cid/ciu629. Source
10. Townes JM, Deodhar AA, Laine ES, et al. Reactive arthritis following culture-confirmed infections with bacterial enteric pathogens in Minnesota and Oregon: a population-based study. Annals of the Rheumatic Diseases. 2008;67(12):1689-1696. doi:10.1136/ard.2007.083451. Source
11. Centers for Disease Control and Prevention. Clinical care of cyclosporiasis. Accessed September 20, 2026. Source
12. Khan I, Bai Y, Zha L, et al. Mechanism of the gut microbiota colonization resistance and enteric pathogen infection. Frontiers in Cellular and Infection Microbiology. 2021;11:716299. doi:10.3389/fcimb.2021.716299. Source
13. National Library of Medicine. How to understand your lab results. MedlinePlus. Accessed September 20, 2026. Source
14. National Institute of Diabetes and Digestive and Kidney Diseases. Diagnosis of irritable bowel syndrome. Accessed September 20, 2026. Source
15. Centers for Disease Control and Prevention. Clinical guidance for cyclosporiasis. Accessed September 20, 2026. Source
Pam Killeen is a health coach and nutritional consultant with nearly forty years of experience helping people restore the foundations of their health. Her own recovery from chronic fatigue, fibromyalgia, and multiple chemical sensitivities shaped the approach she teaches today. She co-authored Dr. Joseph Mercola’s New York Times bestseller The Great Bird Flu Hoax and is the author of Addiction: The Hidden Epidemic and Survival of the Unfittest. She is the creator of the Circadian Reboot and Truth Over Spin podcasts.
Her new book, Parasites & the Terrain: How Circadian Rhythm, Sunlight, and Minerals Build Natural Resistance, with a foreword by Dr. Mercola, will be published by Skyhorse Publishing on January 19, 2027. Read more and preorder here.