Small bowel bacterial overgrowth
Small bowel bacterial overgrowth is a condition in which very large numbers of bacteria grow in the small intestine.
Overgrowth - intestinal bacteria; Bacterial overgrowth - intestine; Small intestinal bacterial overgrowth; SIBO
Most of the time, the small intestine does not have a high number of bacteria. Excess bacteria in the small intestine may use up the nutrients needed by the body. As a result, a person may become malnourished.
The breakdown of nutrients by the excess bacteria can also damage the lining of the small intestine. 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 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 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 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).
The most common symptoms are:
- Abdominal fullness
- Abdominal pain and cramps
- Diarrhea (usually watery)
Other symptoms may include:
- Fatty stool
- Weight loss
Exams and Tests
Your health care provider will perform a physical exam and ask about your medical history. Tests may include:
- 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
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).
Severe cases lead to malnutrition. Other possible complications include:
Manolakis CS, Rutland TJ, Di Palma JA. Small intestinal bacterial overgrowth. In: McNalley PR, ed. GI/Liver Secrets Plus. 5th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 44.
Quigley EMM. Small intestinal bacterial overgrowth. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 105.
Reviewed By: Subodh K. Lal, MD, gastroenterologist with Gastrointestinal Specialists of Georgia, Austell, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.