It is the clinical manifestation occurring when there is an abnormal proliferation in the small intestine of normal bacterial flora of the lower digestive tract.

Usually there is normal bacterial flora which colonizes the colon in particular and helps to absorb nutrients and aids in the synthesis of some proteins.

Overgrowth occurs when the bacteria in the colon invade determined parts of the small intestine.

Several etiological processes may alter the mechanisms which keep the number of these bacteria low:

• Structural anomalies (congenital or surgical)
• Disorders causing reduced gastric acidity
• Reduction of the intestinal motility
• Damaged or atrophic intestinal mucous

The clinical manifestations of the bacterial overgrowth syndrome are based on the increasing bacterial load which jeopardizes the normal functions of the upper gastrointestinal system.

The following symptoms, among others, stand out:

• Abdominal distension
• Weight loss
• Steatorrhea (foul-smelling feces)
• Watery diarrhea
• Megaloblastic anemia
• Neurological signs due to vitamin B12 deficiency

The early recognition and treatment of bacterial overgrowth syndrome must be targeted at preventing and reverting malabsorption processes.

The treatment frequently used in cases of bacterial overgrowth is usually broad-spectrum antibiotic therapy.

Treatment must always be that indicated by the prescribing physician.

There are different types of diagnostic tests:

• HYDROGEN BREATH TEST: This is a non-invasive test that is easy to perform and can also be useful in the diagnosis of diseases such as cystic fibrosis, hyperglycemia, orocecal transit time, gastroesophageal reflux and celiac disease. It can also be applied to evaluate the therapeutic efficacy of drugs against myeloid leukemia and to study the negative effects of lactose absorption due to HIV
• Collecting stools to check for the presence of steatorrhea
• X-rays of the small intestine
• Small intestine biopsy
• Aspiration and culture of proximal jejunum secretion

• H₂-LACTULOSE
• H₂-GLUCOSE
• H₂-XYLOSE
• ...

• Wetzel, KH2 Breath test for medical research and clinical diagnosis.
  
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  Gastroenterol J Taiwan Vol. 16, Nº 1.
• Perman, J.A. Clinical application of breath hydrogen measurements.
  (1991) Can. J. Physiol. Pharmacol. Vol. 69.
• Hsu HW, Butte NF, Wong WW et al. (1997): Oxidative Metabolism in Insulin-Treated Gestational Diabetes Mellitus.
  Am J Physiol 272, E 1099 – E 1107
• Stellaard F, Koetse A, Elzinga H et al. (2000): 13C-Carbohydrate Breath Test: Impact of Physical Activity on the Rate-limiting Step in Lactose Utilization.
  Scand J Gastroenterol 35, 819 – 823