Post-infectious IBS: IBS that starts after a stomach bug

Irritable bowel syndrome (IBS) is a common condition of the digestive system. The NHS says it is usually a lifelong problem with symptoms that come and go over time, and that the exact cause is unknown but it has been linked to food passing through the gut too quickly or too slowly, gastroenteritis, oversensitivity in the gut, stress and a family history of IBS.

Post-infectious IBS is the form that begins after an acute gut infection. A research paper on the topic describes acute infectious gastroenteritis as the most commonly identified trigger for IBS, and says that the Rome Foundation has proposed diagnosing PI-IBS as new-onset, Rome criteria-positive IBS, with symptoms developing immediately after resolution of acute gastroenteritis. Infection with bacteria such as Campylobacter, Salmonella, Shigella and E. coli, with the protozoan Giardia, and with norovirus have all been associated with it.

Guts UK explains that doctors know IBS as a disorder of gut-brain interaction, in which the nerves supplying the gut can be too sensitive to the way the bowel normally moves, and that for some people a gut infection or antibiotic use can cause the condition to start.

Most people recover fully from gastroenteritis. A minority go on to have ongoing symptoms. The only figures in the sources used here come from a Mayo Clinic and Minnesota Department of Health study of people with laboratory-confirmed Campylobacter infection: of 1,418 survey responders without pre-existing IBS, 301 (21%) subsequently developed IBS 6 to 9 months later. Because the people who respond to a survey after a notified infection may differ from everyone who has a stomach bug, the true rate in the general population will be different.

In that study, most people who developed PI-IBS had IBS-mixed (54%) or IBS with diarrhoea (38%), and a small proportion (6%) had IBS with constipation. Female sex, younger age, bloody stools, abdominal cramps and hospitalisation during the acute illness were associated with increased risk, whereas fever was associated with lower risk. Antibiotic use and exposure patterns were similar between those who developed PI-IBS and those who did not.

The study also found that among people who already had IBS, 38% had increased frequency of abdominal pain after the Campylobacter infection, and that the IBS subtype could change after infection.

Symptoms are those of IBS in general. The NHS lists stomach pain or cramps, usually worse after eating and better after doing a poo; bloating; diarrhoea; and constipation. Guts UK says the pain happens, for diagnostic purposes, on average one day a week or more for at least three months and is associated with a change in bowel habit. Other symptoms the NHS lists include wind, mucus in poo, tiredness, feeling sick, backache, bladder problems and pelvic pain.

The distinguishing feature of PI-IBS is the timing: symptoms begin after a clear episode of infectious gastroenteritis in someone who did not have IBS before. The NHS notes that symptoms can be triggered by alcohol, caffeine, spicy or fatty food, stress and anxiety and regular antibiotic use.

The NHS says there is no test for IBS. The GP will ask about your symptoms, when they started and what makes them better or worse, and may feel your tummy. You might need blood tests to check for problems like coeliac disease and tests on a poo sample for infections and inflammatory bowel disease (IBD). Guts UK adds checks for anaemia and for how well the liver and kidneys are working, and a faecal calprotectin stool test which, if normal, can help show that symptoms are not caused by Crohn’s disease or ulcerative colitis.

Guts UK says that after ruling out other conditions with a few simple tests, doctors can be confident that the diagnosis is IBS. A clear history of an infectious illness shortly before the symptoms began is what leads to the post-infectious label; the sources used here describe the same approach to ruling out other conditions as for IBS in general.

Guts UK lists symptoms that are not typical of IBS and may signal other diseases: a persistent change of bowel habit for 4 weeks or longer, especially if you are over 40, are passing blood from the back passage, have unintentional weight loss of more than 2kg, have diarrhoea that wakes you from sleep, have a fever or have been diagnosed with anaemia. Tell your doctor about a family history of bowel cancer, colitis or Crohn’s disease. This applies even if you already have a diagnosis of IBS.

The NHS says to ask for an urgent GP appointment or contact NHS 111 if you have lost a lot of weight for no reason, are bleeding from your bottom or have bloody diarrhoea, find a hard lump or swelling in your tummy, or have shortness of breath, palpitations and paler skin than usual.

The sources used here do not describe a treatment that is specific to PI-IBS, so management follows that for IBS in general. Guts UK says most people can find effective ways to live with IBS once diagnosed, and that treatment may need to be altered according to the symptoms: regular exercise, healthy eating habits (three regular meals, limiting alcohol and caffeine, eating small portions slowly), and adjusting fibre according to whether diarrhoea or constipation predominates.

If simple dietary changes do not help, the GP may refer you to a dietitian. Guts UK says only state-registered dietitians are trained to advise on exclusion diets such as the low FODMAP diet, which it says works for about half to two thirds of people with IBS, and that you should not try exclusion diets on your own. It also says trying a probiotic for up to 12 weeks is recommended, with continuing only if there is improvement. Medicines for symptoms may be suggested by your GP depending on whether pain, diarrhoea or constipation is the main problem.

The NHS describes IBS as usually a lifelong problem, but one where diet changes and medicines can often help control the symptoms. The sources used here do not give a recovery time specific to post-infectious IBS, and individual experience varies. It is worth keeping a symptom and food diary and returning to your GP if the pattern changes or red-flag symptoms appear.

If your symptoms started after antibiotics or after foreign travel, tell your clinician, since Guts UK says antibiotic use can start IBS in some people and the NHS lists regular antibiotic use as a trigger of symptoms.