What are the diagnosis criteria for post-infectious irritable bowel syndrome (IBS) in a patient with a recent gastrointestinal infection and chronic abdominal pain, bloating, and changes in bowel habits?

Diagnostic Criteria for Post-Infectious IBS

Post-infectious IBS is diagnosed when a patient develops recurrent abdominal pain (at least 1 day per week) associated with changes in defecation, stool frequency, or stool form, with symptoms beginning immediately after documented acute infectious gastroenteritis and no prior IBS diagnosis before the infection. 1

Essential Diagnostic Requirements

Temporal Relationship to Infection

• The critical distinguishing feature is the patient's ability to recall a precise date of symptom onset following an infectious episode 1
• Symptoms must develop immediately following resolution of acute infectious gastroenteritis 1, 2
• The patient must not have met IBS criteria prior to the acute infectious illness 1, 2

Documented Infection Criteria

• Either positive stool culture OR presence of ≥2 acute symptoms during the initial gastroenteritis episode (fever, vomiting, diarrhea) is necessary for diagnosis 1, 3
• Approximately 10% of IBS patients report onset following acute enteric infection 4

Rome IV Symptom Criteria

• Recurrent abdominal pain occurring on average at least 1 day per week in the last 3 months 1
• Symptom onset must be at least 6 months before diagnosis 1, 2
• Pain must be associated with ≥2 of the following:
  • Related to defecation 1, 2
  • Associated with a change in frequency of stool 1, 2
  • Associated with a change in form (consistency) of stool 1, 2

Characteristic Clinical Features

Predominant Symptom Patterns

• Most post-infectious IBS cases present as diarrhea-predominant or mixed-type, rather than constipation-predominant 1
• Mixed-type symptoms are characterized by alternating between diarrhea and constipation, with variable stool consistency 1
• Post-infectious IBS differs from non-infective IBS by having more diarrheal features 5

Supportive Clinical Features

• Bloating is not required for diagnosis but, if present, is highly suggestive of IBS and often accompanied by visible abdominal distension 4
• The diagnosis is more likely if the patient is female and aged <45 years 4

Baseline Investigations

Required Initial Testing

• Full blood count, C-reactive protein or erythrocyte sedimentation rate, and coeliac serology 4
• Faecal calprotectin if diarrhea is present and age <45 years 4

Exclusion of Red Flag Features

• Ensure absence of weight loss, rectal bleeding, nocturnal symptoms, or anemia 4, 6
• Normal physical examination is expected 4

Common Diagnostic Pitfalls

Critical Errors to Avoid

• Failing to document the temporal relationship between infectious gastroenteritis and IBS symptom onset is a common pitfall in diagnosis 1
• Not recognizing that some patients may experience irregular bowel movements prior to the acute illness and can still be defined as developing post-infectious IBS 2
• Failing to distinguish between symptom improvement and complete resolution when determining ongoing diagnostic criteria 2, 7

Important Considerations

• The diagnostic label of post-infectious IBS is removed after complete symptom resolution, as it is defined by the presence of ongoing symptoms that meet Rome IV criteria 2
• Recovery is defined as resolution of symptoms to the point where Rome IV criteria are no longer met 2, 7

Prognosis and Natural History

Recovery Timeline

• Patients face a 4.2-fold increased risk of IBS within the first 12 months after infection, which decreases to 2.3-fold beyond 12 months 7
• Less than half of post-infectious IBS cases recover over six years 5
• A history of anxiety and depression severe enough to warrant treatment may impair recovery 5, 7