December 2017 Issue

Digestive Health: Postinfectious IBS — The Link Between Gastroenteritis and This Troublesome Digestive Disorder
By Carrie Dennett, MPH, RDN, CD
Today's Dietitian
Vol. 19, No. 12, P. 12

Irritable bowel syndrome (IBS) is a chronic functional bowel disorder that causes abdominal pain with diarrhea, constipation, or both, likely affecting around 10% of the US population.1,2 While most people with IBS can't pinpoint the onset of their symptoms, it's estimated that 10% of IBS patients can identify that symptoms started after an episode of acute infectious gastroenteritis caused by bacteria or another pathogen.1,2 This type of IBS has a name: postinfectious IBS (PI-IBS).

Here's what dietitians should know if patients wonder why they're having digestive distress long after recovering from a bout of food poisoning.

What Is PI-IBS?
PI-IBS was first identified in 1950, and researchers started to get a sense of its prevalence in 1962.3 Depending on the study, the percentage of individuals who develop IBS after a case of gastroenteritis may be as high as 30% to 40%.1,2,4 "We probably encounter PI-IBS more often than we realize," says Patsy Catsos, MS, RDN, LD, author of The IBS Elimination Diet and Cookbook: The Proven Low-FODMAP Plan for Eating Well and Feeling Great.

Several pathogens are thought to cause chronic gastrointestinal (GI) conditions such as IBS after the acute infection has passed. These include the bacteria Campylobacter jejuni, Salmonella enterica, Shigella sonnei, E coli 0157:H7, and Clostridium difficile. PI-IBS also may follow infection caused by norovirus or the protozoa Giardia lamblia. Roughly one-half of the studies on PI-IBS have involved infection with a single known organism, while the others have involved infections with more than one pathogen or have been associated with cases of traveler's diarrhea where the pathogen usually is unknown.5

Symptoms of PI-IBS tend to involve diarrhea rather than constipation and may persist for eight to 10 years after the initial infection. One study that followed up on an outbreak in which patients were infected by both E coli 0157:H7 and C jejuni found that 36% had PI-IBS after two years, and 15% still had symptoms at eight years. Bacterial infections are associated with longer duration of IBS symptoms,5 as well as a longer period of risk—one meta-analysis found that individuals who had an episode of bacterial gastroenteritis were six times more likely to develop IBS within one year of that episode, and had a four-fold risk three years after the episode.6 Catsos says because the risk of new onset IBS remains high for months after a bout of gastroenteritis, it can be difficult to determine any correlation.

Campylobacter, typically contracted from chicken or other poultry, is one of the top four organisms responsible for foodborne illness in the United States, and C jejuni infection is associated with a 9% to 13% risk of developing PI-IBS.5 Although research on the risk of PI-IBS following infection with C diff is minimal, one recent Mayo Clinic study involving 205 patients with confirmed C diff infection found that 25% reported symptoms consistent with IBS more than six months postinfection.7

Catsos cites one recent patient, a middle-aged, otherwise healthy female who contracted C diff while helping care for a relative in hospice. "The infection did respond to treatment and she is now negative for C diff. But she continues to have frequent loose stools, excessive gas, and bloating, and her doctor diagnosed her with postinfectious IBS," she says.

Norovirus causes as many as 21 million cases of acute gastroenteritis in the United States each year.8 Patients who develop IBS after a bout of gastroenteritis caused by norovirus tend to see resolution of IBS symptoms within one year, making it more transitory than PI-IBS caused by bacteria.5

Although it's difficult to determine incidence of PI-IBS following traveler's diarrhea, one meta-analysis developed a conservative estimate that individuals who suffer from traveler's diarrhea have three times the risk of developing IBS.9 Many epidemiologic studies have demonstrated that infection with G lamblia, which typically results from ingesting contaminated food or water, is a risk factor for PI-IBS, with one study finding a 36% PI-IBS rate following an outbreak.9

Another of Catsos' IBS patients is a young man with GI symptoms and unintentional weight loss two years after traveling extensively in Africa and Asia, where he'd drunk untreated water. "He had some diarrhea and fever while traveling, and by the time he returned to the United States, he had increasingly frequent bouts of symptoms and lost 20 lbs over a short period of time," she says, adding that the patient had excellent care at a world-class GI clinic, where providers found no evidence of parasites and no organic cause for his abdominal pain, excessive gas, bloating, and diarrhea. "Although not formally diagnosed with postinfectious IBS, this history might be consistent with the diagnosis."

Pathogenic bacteria can disturb the resident microbial community and compromise the integrity of the epithelial cell barrier lining the intestines, increasing gut permeability.1,2,10 Increased gut permeability generally is considered to be an "early event" in IBS, especially IBS with diarrhea.2 Regardless of the pathogenic organism, it appears that exposure alters intestinal motility and triggers chronic inflammation and intestinal immune activation, leading to the persistence of symptoms even after the pathogen has cleared the body.1,3,11

Who's Most Likely to Get PI-IBS?
"The cause of IBS is still an open question. It's likely to be multifactorial," Catsos says. "A bout of gastroenteritis might interact with other factors, which predispose a person to IBS."

The risk of developing PI-IBS appear to be higher with more severe cases of infectious gastroenteritis, especially if prolonged or bloody diarrhea is involved.3,9 Fever and/or weight loss during the acute infection increases the risk of developing PI-IBS, as does treatment with antibiotics.9 Intestinal infection may trigger the initial symptoms, but certain psychological profiles may contribute to prolonging them,6 including depression, anxiety, hypochondria, or stressful life events in the preceding three months.2,5,9 In addition, researchers have found four genetic variants that may be associated with PI-IBS.11 Being younger and female is associated with increased risk.2,5,9 And all of these factors may pertain more to PI-IBS with a bacterial origin than with a norovirus origin.12

What Should RDs Consider?
Catsos says it's unusual for patients to have a positive diagnosis of PI-IBS. "The anecdotes I hear from patients with sudden-onset IBS seem to be related to bouts of foodborne illness more often than not," she says. "Most cases are simply chalked up to food poisoning unless there has been a communitywide outbreak, so patients aren't likely to know whether the specific pathogen involved was viral or bacterial."

Currently, there's no valid biomarker for IBS.2 Because of this, diagnosis often requires eliminating more serious GI diseases, such as inflammatory bowel disease (eg, Crohn's disease and ulcerative colitis), celiac disease, and nonceliac wheat sensitivity (formerly called nonceliac gluten sensitivity). While IBS may be diagnosed by eliminating other possibilities, diagnosis based on symptoms is in line with current recommendations. The Rome IV criteria for colorectal disorders specify that IBS is characterized by recurrent abdominal pain for at least one day per week in the last three months, on average, associated with two or more of the following criteria13,14:

• related to defecation;
• associated with a change in frequency of stool; and
• associated with a change in form (appearance) of stool.

Symptom onset must occur at least six months before diagnosis.13,14 Other symptoms that may support an IBS diagnosis include variations in stool consistency and frequency or an unpredictable bowel pattern, abnormal stool frequency (more than three bowel movements per day or less than three per week), excessive straining during bowel movements, urgency (needing to rush to the toilet), feelings of incomplete evacuation, and mucus with bowel movements.2

In most patients, PI-IBS will resolve gradually and spontaneously when untreated, but given that IBS can greatly affect quality of life, appropriate treatment is still warranted, and that treatment is the same as for other cases of IBS, including nutrition therapy, such as the low-FODMAP (fermentable oligo-, di-, monosaccharides and polyls) diet, or drug therapy. Because changes to the gut microbiota from gastroenteritis aren't completely understood, currently there's no definitive therapy.11

Catsos says dietitians who follow the evolving research on small intestinal bacterial overgrowth (SIBO) may be more aware of PI-IBS, because PI-IBS and SIBO may be closely entwined. "While it isn't within our scope of practice to evaluate whether a patient has PI-IBS or not, knowing a patient's history of foodborne illness might make me more likely to recommend the patient be evaluated or treated for SIBO if symptoms persist," she says.

— Carrie Dennett, MPH, RDN, CD, is the nutrition columnist for The Seattle Times and speaks frequently on nutrition-related topics. She also provides nutrition counseling via the Menu for Change program in Seattle.

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13. Mearin F, Lacy BE, Chang L, et al. Bowel disorders. Gastroenterology. 2016;150(6):1393-1407.e5.

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