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

• Bloating, flatulence, abdominal pain, diarrhea, and sometimes steatorrhea with weight loss

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

• Severe cases may result in clinically significant vitamin and mineral deficiencies, including

  • Fat-soluble vitamins A or D

  • Vitamin B₁₂

  • Iron

Diagnosis

• Noninvasive breath hydrogen and methane tests with glucose or lactulose as substrates are generally preferred because of their ease of use

• Following ingestion of glucose 75 g or lactulose 10 g,

  • A rise in exhaled breath hydrogen of 20 ppm or methane ≥ 10 ppm within 90 minutes suggests bacterial overgrowth

  • Has 65% diagnostic agreement with small bowel cultures

• 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

• A specific diagnosis can be established firmly only by an aspirate and culture of distal duodenal secretion that demonstrates over 10³ organisms/mL

Treatment

• Correct the anatomic defect when possible

• Otherwise, treatment for 7–10 days with oral broad-spectrum antibiotics improves symptoms in up to 90% of patients for weeks to months

• Recommended regimens include

  • Ciprofloxacin 500 mg orally twice daily

  • Norfloxacin 400 mg orally twice daily

  • Amoxicillin clavulanate 875 mg orally twice daily

  • Trimethoprim-sulfamethoxazole (one double-strength tablet) orally twice daily

  • Rifaximin 400–550 mg orally three times daily

  • A combination of neomycin 500 mg orally twice daily plus metronidazole 250 mg orally three times daily