Gastroenterology
Small Intestinal Bacterial Overgrowth
소장세균과증식
Excess bacteria in small bowel causing malabsorption and gaseous symptoms
- How common
- 30%+ of IBS patients
- Typical age
- Middle-aged and older
What is it?
Impaired motility, reduced acid, anatomic abnormalities allow colonic bacteria to overgrow in small bowel.
Commonly affected: Small bowel (especially jejunum)
How it develops
- Defense impairmentReduced acid, dysmotility, ileocecal valve defect
- Bacterial overgrowthSmall bowel ≥10⁵ CFU/mL
- Nutrient fermentationBile acid deconjugation, B12 consumption, fat malabsorption
- SymptomsBloating, diarrhea, weight loss, micronutrient deficiency
Symptoms
- Bloating/gasWorse postprandial
- Diarrhea/steatorrheaBile acid/fat malabsorption
- Weight lossResult of malabsorption
- B12/iron deficiencyMicronutrient depletion
- Discomfort/nauseaNon-specific
How it is examined
- Assess risk factorsDM, gastrectomy, scleroderma, PPI, IBS, ICV resection
- H2/CH4 breath testGlucose or lactulose load
- Small bowel aspirate culture≥10³-10⁵ CFU/mL = positive (gold standard)
Imaging
SBFT for diverticula, strictures, blind loops.
- Diverticula
- Stricture
- Blind loop
CT/MR enterography for anatomic abnormalities.
- Bowel dilatation
- Anatomic abnormality
Non-surgical care
- Rifaximin x 14d550mg TID (first-line)
- Methane+: rifaximin + neomycinEffective for methane-predominant (IMO)
- Treat underlying causeProkinetic, taper PPI
- Low-FODMAP/elemental dietTry if refractory
- Micronutrient repletionB12, iron, vitamins ADEK
Conservative options are generally tried first. Medications listed here can have side effects — discuss them with your prescriber.
When surgery is considered
Anatomic cause (diverticula, blind loop, stricture)
Procedures that may be discussed
- Diverticulectomy
- Blind loop revision
- Strictureplasty
Outlook
Rifaximin response 60-70%; relapse common, may need repeat courses.