Bacterial Overgrowth Syndrome Clinical Presentation

Updated: Mar 07, 2023
  • Author: Chinelo N Animalu, MD, MPH, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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No specific symptoms are pathognomonic for bacterial overgrowth syndrome (BOS). Nonetheless, various nonspecific GI symptoms are common in affected individuals. Clinicians should have a heightened clinical suspicion for bacterial overgrowth syndrome in patients who present with the following:

  • Bloating

  • Flatulence

  • Abdominal pain

  • Diarrhea

  • Dyspepsia

  • Weight loss

Advanced cases of bacterial overgrowth syndrome may manifest as malabsorption findings, as follows:



Disorders or structural abnormalities that disrupt the protective mechanisms that guard against increasing bacterial burden can lead to bacterial overgrowth syndrome.

Patients with the following medical conditions are at increased risk for bacterial overgrowth syndrome:

  • History of upper intestinal tract surgery

  • Irritable bowel syndrome [7]

  • Liver cirrhosis [2, 4]

  • Celiac disease [8, 9]

  • Immune deficiency (eg, AIDS, IGA deficiency, severe malnutrition) [2, 4]

  • Short bowel syndrome [2]

  • End stage renal disease [4]

  • Gastrojejunal anastomosis

  • Vagotomy, but not selective parietal cell vagotomy

  • Antral resection

  • Pancreatic exocrine insufficiency

Abnormal small intestinal motility due to the following may result in bacterial overgrowth syndrome:

Blind pouches from the following may result in bacterial overgrowth syndrome:

  • Side-to-side or end-to-side anastomoses

  • Intra-abdominal reservoirs

  • Duodenal or jejunal diverticula

  • Segmental dilatation of the ileum

  • Blind loop syndrome

  • Biliopancreatic diversion

Abnormal bowel communication due to the following may cause bacterial overgrowth syndrome:

Partial obstruction caused by the following may result in bacterial overgrowth syndrome:

Reduced gastric acid secretion from the following may result in bacterial overgrowth syndrome:

  • Vagotomy

  • Long-term administration of proton pump inhibitors [10]

Prevalence of BOS rises with age. [4, 11]


Physical Examination

A complete physical examination should be performed with emphasis on abdominal examination and examination for signs of malabsorption of various nutrients. No specific physical examination techniques are required for bacterial overgrowth syndrome.



Complications of bacterial overgrowth syndrome are possible in patients with prolonged and untreated symptoms, potentially leading to increased morbidity and mortality in higher-risk patients (eg, the very young and elderly).

Malabsorption of iron, vitamin B-12, and folate can lead to anemia

Persistent diarrhea can lead to volume loss and electrolyte disturbances.

Decreased fat absorption can lead to further diarrhea.