Small intestinal bacterial overgrowth (SIBO) is a condition where a person's own good and useful germs, live in parts of the bowel where there should not be any germs. It may cause difficult tummy and bowel symptoms in a wide variety of patient groups. Increasing evidence suggests that sometimes small intestinal bacterial overgrowth can also trigger or worsen diseases which do not have any bowel symptoms at all.

It is hugely under-diagnosed in clinical practice. Part of the reason for this is that current available diagnostic tests - culture of fluid sampled from the upper part of the gastrointestinal tract or breath testing, are complicated to do, difficult for the patient, and are not completely accurate. Therefore, the potential for a simple, more accurate test to revolutionise the diagnosis and aid with the treatment of this condition is immense.

When it is accurately diagnosed, treatment with antibiotics can cure the patient of their tummy or bowel symptoms.

Based on previous research the investigators have conducted, it is believed that it might be possible to diagnose this condition in a simpler and more accurate way by examining urine samples. This study will also investigate whether the condition could be diagnosed more accurately using a blood test, a different sort of breath test or using a mouth swab.

The proposed study will be conducted at Lincoln County Hospital, in collaboration with Joseph Banks Laboratory at the University of Lincoln. Additional urine, blood, swab and breath samples from patients with and without small intestinal bacterial overgrowth, before and after antibiotic treatment to identify specific molecular markers in urine, blood and saliva samples which diagnosis small intestinal bacterial overgrowth accurately.

Inclusion Criteria:

1. Adults aged ≥ 18 and ≤ 50
2. Absence of red flag symptoms i.e. unexplained weight loss, a palpable mass, unexplained iron deficiency anaemia or rectal bleeding
3. GI symptoms which are due to possible SIBO
4. Capacity to give informed consent

Exclusion Criteria:

1. Presence of red flag symptoms (specified above in inclusion criteria)
2. Previous GI surgery including cholecystectomy (except appendicectomy, inguinal/femoral hernia repair or Caesarean sections)
3. Past history of inflammatory bowel disease, coeliac disease or pancreatic disease
4. Past history of cancer (except basal cell carcinoma)
5. Female patients who are pregnant
6. Inability to adequately understand verbal or written information
7. Inability or unwillingness to give informed consent
8. Unwilling to consider taking antibiotics to treat SIBO
9. Incapacity to comply with the demands of the study

All patients who are referred to Lincoln County Hospital for assessment of chronic diarrhoea will be considered eligible. They will be further assessed in a gastroenterology clinic using the inclusion and exclusion criteria