Bacterial Overgrowth, Small Intestine

Key Features

• Overgrowth of bacteria in normally sterile segments of small bowel; may result in malabsorption of fat with steatorrhea

• Causes include

  • Gastric achlorhydria

  • Anatomic abnormalities of the small intestine with stagnation (afferent limb of Billroth II gastrojejunostomy, resection of ileocecal valve, small intestine diverticula, obstruction, blind loop)

  • Small intestine motility disorders (vagotomy, scleroderma, diabetic enteropathy, chronic intestinal pseudo-obstruction)

  • Gastrocolic or coloenteric fistula (Crohn disease, malignancy, surgical resection)

  • Miscellaneous disorders

Clinical Findings

• Many patients are asymptomatic

• Flatulence, weight loss, abdominal pain, diarrhea, and sometimes steatorrhea

• May also be present in a subset of patients with irritable bowel syndrome

• Advanced cases associated with deficiencies of iron or vitamins A, D, and B₁₂

Diagnosis

• Stool fecal fat: corroborates presence of steatorrhea

• Small bowel CT or MR enterography or barium radiography: identifies mechanical factors predisposing to intestinal stasis

• Small intestinal biopsy

  • Excludes other mucosal malabsorptive conditions (eg, celiac disease)

  • Detects intestinal inflammation

• Aspirate and culture of proximal jejunal secretion

  • > 10⁵ organisms/mL establishes the diagnosis

  • However, this test is not widely available

• Noninvasive breath tests are reported to have a sensitivity of 60–90% and specificity of 85% compared with jejunal cultures

Treatment

• Correct the anatomic defect when possible

• Ciprofloxacin, 500 mg twice daily orally, norfloxacin, 400 mg twice daily orally, amoxicillin clavulanate, 875 mg twice daily orally, or combination of metronidazole, 250 mg three times daily orally, and trimethoprim-sulfamethoxazole 160/800 mg twice daily orally, or cephalexin, 250 mg four times daily orally, for 1–2 weeks

• Rifaximin, 400 mg three times daily orally, is a nonabsorbable antibiotic that is effective and appears to have fewer side effects than systemic antibiotics

• If symptoms recur off antibiotics, cyclic therapy (eg, 1 week of every 4) may be sufficient

• Avoid continuous antibiotics to prevent bacterial antibiotic resistance

• Octreotide in small doses may be of benefit