Small intestinal bacterial overgrowth
Small intestinal bacterial overgrowth (SIBO) is an excessive bacterial growth in the small intestine which in contrast to the large intestine in healthy individuals contains relatively small populations of bacteria.
The rate of a positive lactulose test is low in healthy adults (0 to 20%).
Anecdotal reports suggest a high prevalence of SIBO among CFS patients. One study found 77% of CFS patients had SIBO and eradication lead to decrease in symptoms. Several studies have shown that up to 84% of patients with irritable bowel syndrome have SIBO and that symptoms improve after treatment, while others fail to replicate these results.
One study found that a 100% of fibromyalgia patients tested positive to a lactulose breath test, indicating SIBO, and that the degree of abnormality on the breath test correlated with the amount of pain reported. Patients with CFS have alterations in microbiota, including lower levels of bifidobacteria and SIBO
Risk factors include bowel resection, bariatric surgery, disordered motility, disorders of the immune system such as IgA deficiency, low stomach acid, the use of proton pump inhibitors and immunosuppressants, and recurrent antibiotic use.
SIBO is more common among the elderly.
SIBO can be diagnosed using a hydrogen breath test. The diagnosis of SIBO is controversial due to the species-dependent nature of breath tests and the lack of an agreed threshold for a positive test. It can also be diagnosed through bacterial culture, but this is rare as it requires intubation of the small intestine.
Bacteria commonly implicated in SIBO include Escherichia coli, Streptococcus, Lactobacillus, Bacteroides and Enterococcus. Higher levels of Enterococcus and Stretptococcus have been found in ME/CFS patients.
The symptoms of SIBO can vary greatly depending on the severity and the species of bacterial populating the small intestine. Symptoms include bloating, abdominal distension, abdominal pain or discomfort, diarrhea, fatigue, and weakness.
SIBO can also cause carbohydrate and protein malabsorption.
Standard treatment is a course of antibiotics.  The best evidence for patients without constipation is for the use of rifaximin, an antibiotic that is stays in the intestine and is not absorbed in the body. Some SIBO researchers recommend adding Neomycin to rifaxamin for patients with constipation, as neomycin appears to help kill methane-producing bacteria.  However, one study comparing two herbal formulations to standard treatment found herbs to be as or more effect as antibiotics for eradicating SIBO.
Probiotics may also be helpful. Lactobacillus casei has been found to improve breath hydrogen scores after six weeks of treatment. There is also evidence for VSL #3 in the treatment of SIBO. However, some probiotics may exacerbate SIBO, in particular those containing D-Lactate producing strains.
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