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Small bowel bacterial overgrowth

Small bowel bacterial overgrowth is a condition in which very large numbers of bacteria grow in the small intestine.

Causes

Unlike the large intestine, the small intestine does not have a high number of bacteria. When there are too many bacteria in the small intestine, these organisms use up the nutrients that would otherwise be absorbed into the body. A person with small bowel bacterial overgrowth may become malnourished as a result.

The breakdown of nutrients in the small intestine by the excess bacteria can also damage the intestinal lining. This can make it even harder for the body to absorb nutrients.

Conditions that can lead to overgrowth of bacteria in the small intestine include:

  • Complications of diseases or surgery that create pouches or blockages in the small intestine. Crohn's disease is one of these conditions.
  • Diseases that lead to movement problems in the small bowel, such as diabetes and scleroderma
  • Immunodeficiency such as AIDS or immunoglobulin deficiency
  • Short bowel syndrome caused by surgical removal of part of the small intestine
  • Small bowel diverticulosis, in which small sacs occur in the inner lining of the intestine. These sacs allow too many bacteria to grow. These sacs can occur anywhere along the intestinal tract, but they are much more common in the large bowel.
  • Surgical procedures that create a loop of small intestine where excess bacteria can grow. An example is a Billroth II type of stomach removal (gastrectomy).
  • Some cases of irritable bowel syndrome (IBS)

Symptoms

The most common symptoms are:

  • Abdominal fullness
  • Abdominal pain and cramps
  • Bloating
  • Diarrhea (usually watery)
  • Gassiness

Other symptoms may include:

  • Fatty stool
  • Weight loss

Exams and Tests


  • Blood chemistry tests (such as albumin level)
  • Complete blood count (CBC)
  • Fecal fat test
  • Small intestine x-ray
  • Vitamin levels in the blood
  • Small intestine biopsy or culture
  • Special breath tests

Treatment

The goal is to treat the cause of the bacterial overgrowth. Treatment most often consists of antibiotics. In some cases, drugs that speed intestinal movement (motility-speeding drugs) may be used. A low carbohydrate diet can be helpful.

Treatment also involves getting enough fluids and nutrition. A person who is dehydrated may need intravenous (IV) fluids in a hospital. A person who is malnourished may also need nutrition given through a vein (total parenteral nutrition -- TPN).

Possible Complications

Severe cases lead to malnutrition. Other possible complications include:

Alternative Names

Overgrowth - intestinal bacteria; Bacterial overgrowth - intestine

References

Semrad CE. Approach to the patient with diarrhea and malabsorption. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 142.

Update Date: 5/15/2014

Updated by: Jenifer K. Lehrer, MD, Department of Gastroenterology, Frankford-Torresdale Hospital, Aria Health System, Philadelphia, PA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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