Irritable bowel syndrome with diarrhea (IBS-D) is commonly encountered in clinical practice. The underlying pathophysiology is multifactorial. We talked with Ali Rezaie, MD, recently about why physicians should be aware of a certain subgroup of IBS-D patients: those with post infectious IBS.

PW: What evidence is emerging on postinfectious IBS as it relates to IBS-D?

AR: This generally occurs after a bacterial infection. Viral infections are not as strongly associated with IBS. The bacteria that generally lead to IBS are gram-negative bacilli. Whenever a patient picks up infectious gastroenteritis from these bacteria, there is a roughly 12% chance they will develop IBS.

A proportion of IBS patients who are postinfectious after an incident of infection move on, their symptoms go away, and they live a healthy life. However, for some, symptoms become chronic, resulting in long-term IBS that requires therapy.

It’s not clear how the dots line up for chronic GI disorders like IBS, Crohn’s disease, or even celiac disease. However, for those with postinfectious IBS, we can track the development from cause to onset, which doesn’t happen in many diseases and makes postinfectious IBS captivating.

How common is infectious gastroenteritis as a clear cause of IBS-D?

If a patient develops post infectious IBS as a result of infectious gastroenteritis, generally they will develop IBS with diarrhea (IBS-D) or a mixed type of IBS (IBS-M) that alternates between diarrhea and constipation. Rarely, infectious gastroenteritis can cause IBS with constipation (IBS-C).

The Millennium Cohort Study—which examined the risk factors of military veterans coming home with IBS—found that food poisoning in the field was the main risk factor for developing IBS, higher than any other risk factor, including life stressors, and you can imagine going to war is not a stress-free experience. Essentially, you have a 200% higher chance of IBS if you develop infectious gastroenteritis when deployed.

We know that a certain group of patients, on average 12%, will develop, without a doubt, IBS. The link is 100% established: infectious gastroenteritis causes IBS.

In your practice, is it standard to ask a patient about a history of food poisoning if they are experiencing IBS-D symptoms?

Yes, it is standard. You have to dig a little deeper, though, when questioning the patient. Many patients don’t necessarily recall a bout of infectious gastroenteritis, but test positive for exposure to gram-negative bacilli. It is important to remember to bring this up. It is no surprise that patients don’t always remember experiencing a couple days of diarrhea a year prior, especially because IBS symptoms can take weeks, or even months, to occur. There is an underestimation of postinfectious IBS. I also always ask if the symptoms started with traveling somewhere and if their bowel habits changed when they came back. Those are all clues that infectious gastroenteritis was the lead cause.

Do IBS symptoms related to infectious gastroenteritis have a specific treatment?

Generally speaking, treatment remains relatively similar as with “regular” IBS; however, understanding of the difference of responsive therapies in these patients is emerging. Dietary modifications are the first step. Removing some fermentable foods from the diet can improve symptoms significantly. However, it should be noted that excessively restricted diets can lead to macronutrient and micronutrient deficiencies, and food items must be reintroduced within a few weeks. When these approaches are unsuccessful, OTC medications are used to treat some mild GI symptoms. Prescription medications, like Rifaximin can help with symptoms of diarrhea and abdominal pain. Other medications are available, but these are generally the initial approaches to treatment.

How has recent research on the microbiome impacted the way IBS-D symptoms are addressed?

While the microbiome has been associated with conditions from obesity to psychological disorders to even heart disease, in my opinion, the poster boy of microbiome-associated conditions is IBS. I’ve experienced success with a newly available microbiome-modulating agent in patients with IBS-D, and studies have shown a high response rate in this patient population.