How do you differentiate between Irritable Bowel Syndrome (IBS) and Post-Infectious Irritable Bowel Syndrome (PI-IBS)?

Differentiating Between Irritable Bowel Syndrome (IBS) and Post-Infectious Irritable Bowel Syndrome (PI-IBS)

Post-Infectious Irritable Bowel Syndrome (PI-IBS) is differentiated from general IBS by a clear temporal relationship between an episode of infectious gastroenteritis and the subsequent development of IBS symptoms in an individual without prior IBS. 1

Definition and Diagnostic Criteria

• PI-IBS is characterized by the acute onset of IBS symptoms (according to Rome criteria) following a documented gastrointestinal infection in a person who did not have IBS previously 2
• The diagnosis requires evidence of infectious gastroenteritis confirmed by stool culture, validated molecular biology analyses (e.g., PCR), or the presence of at least two of the following symptoms: fever, vomiting, or diarrhea 1

Key Differentiating Features

Temporal Relationship

• PI-IBS has a clear onset following an episode of infectious gastroenteritis, while conventional IBS typically has a more insidious onset without a clear triggering event 3
• Symptoms typically develop within 3-12 months after the infectious episode 2

Predominant Bowel Pattern

• PI-IBS is most commonly associated with diarrhea-predominant (IBS-D) or mixed bowel habit (IBS-M) patterns 1
• IBS-M is the most predominant pattern in PI-IBS (majority of studies), followed by IBS-D, with IBS-C (constipation-predominant) being relatively uncommon (<10% of cases) 1
• The IBS-D subtype in PI-IBS tends to remain stable over time 1

Pathophysiological Differences

• PI-IBS shows more evidence of ongoing low-grade inflammation and immune activation compared to non-PI-IBS 3
• Specific microbial signatures differ between PI-IBS and general IBS patients:
  • PI-IBS patients show increased levels of Bacteroidetes phylum bacteria 1
  • General IBS patients typically have an increased Firmicutes/Bacteroidetes ratio 1
• PI-IBS patients demonstrate persistent rectal hyper-reactivity and hypersensitivity following infection 1

Risk Factors Specific to PI-IBS

• Type of infectious agent: Bacterial infections (especially Campylobacter, Salmonella, Shigella, Yersinia) are more commonly associated with PI-IBS than viral infections 1
• Other notable pathogens associated with PI-IBS include:
  • Clostridium difficile (up to 25% of cases develop PI-IBS) 1
  • Vibrio cholerae (16.5% of cases) 1
  • Giardia (associated with both PI-IBS and post-infectious functional dyspepsia) 1
• Severity and duration of the initial infectious episode 2
• Female gender and younger age 2
• Psychological comorbidities such as anxiety and depression 2

Diagnostic Approach

• In typical cases of PI-IBS without alarm features, a positive clinical diagnosis can be made without extensive additional diagnostic assessment 1
• Limited testing may include:
  • Complete blood count 1
  • C-reactive protein 1
  • Fecal calprotectin 1
  • Fecal tests to exclude chronic parasitic or protozoal infections (especially giardiasis) 1
• More extensive investigations are warranted in cases with alarm symptoms such as significant weight loss (>10%), gastrointestinal bleeding, or failure to respond to standard IBS treatments 1

Prevalence and Prognosis

• The prevalence of PI-IBS among those suffering from infectious enteritis ranges from 4-36% 1
• A systematic review of 45 studies found a pooled prevalence of 10.1% at 12 months after infectious enteritis 1
• The risk of developing IBS is 4.2-fold higher in patients who have had infectious gastroenteritis compared to uninfected individuals at 12 months follow-up 1
• This risk decreases to 2.3-fold in studies with follow-up beyond 12 months 1
• PI-IBS has been observed in both adult and pediatric populations 1

Management Considerations

• Treatment approaches for PI-IBS are generally similar to those for IBS in general, guided by predominant symptoms 4
• Symptomatic relief can be achieved with:
  • Antidiarrheals 3
  • Antispasmodics 3
  • 5HT3 antagonists 3
  • Mesalamine 3
  • Probiotics 3
  • Low-dose antidepressants 3
• In difficult cases, combination therapy targeting the underlying pathophysiology may be beneficial 3

Common Pitfalls in Diagnosis

• Failing to obtain a clear history of infectious gastroenteritis, as patients may have limitations in recalling milder or remote episodes 1
• Not recognizing the overlap between PI-IBS and post-infectious functional dyspepsia (PI-FD), which can co-occur in up to 44% of patients 1
• Overlooking the possibility of chronic infection rather than post-infectious syndrome 1
• Assuming that all IBS symptoms following infection are PI-IBS without considering other organic causes, especially in patients with alarm features 1