Public health indication: diarrhoea in high-risk people, suspected food poisoning, outbreaks of diarrhoea in the family or community when isolating the organism may help pinpoint the source of the outbreak, contacts of people infected with certain organism or close house-hold contacts of a person with giardia infection.

Arrange emergency admission if the person is vomiting and unable to retain oral fluids or they have features of severe dehydrations/shock.

Investigations: send a faecal specimen for routine microbiological investigation if there is systemic illness, needs hospital admission, antibiotics, blood/pus in the stool, immunocompromised, recent antibiotic/PPI use/been in hospital, after foreign travel, need to exclude infectious cause. Consider blood test if infection/other causes of acute diarrhoea have been excluded and a chronic cause is suspected.

Consider older age group, home circumstances/level of support, fever, bloody diarrhoea, abdominal pain/tenderness, increased risk of poor outcome and drugs when considering admission.

If colorectal cancer suspected refer using suspected cancer pathway.

Carry out abdominal examination to assess for pain, tenderness, distension, mass, increased or decreased bowel sounds, liver enlargement. Consider rectal examination to assess for tenderness, stool consistency, blood, mucus, possible malignancy.

Refer if the diagnosis remains uncertain after a primary care assessment — if infection and the other common causes of acute diarrhoea have been excluded and it is suspected that an episode of acute diarrhoea is due to a chronic cause.

Determine onset, duration, frequency and severity of symptoms. Ask about red flag symptoms. Attempt to confirm the cause eg infection, travel etc. Ask about quantity/character of stool. Ask about fever, vomiting, contact, travel, exposure. New drugs. Stress/anxiety. Abdominal pain. History of radiation. Immunosuppression. Surgery/medical conditions. Assess for complications eg dehydration.

Look for red flag symptoms: unexplained weight loss, unexplained rectal bleeding, persistent blood in the stool, abdominal mass, rectal mass, severe abdominal pain, iron deficiency anaemia, raised inflammatory markers, nocturnal or continuous diarrhoea or both, fever, tachycardia, hypotension or dehydration.

Determine duration, frequency, pattern, severity of symptoms.

Consider features which may suggest an underlying cause - travel abroad, laxative use, other drugs, chronic fatty diarrhoea, previous abdominal surgery, family history of coeliac disease or inflammatory bowel disease, diet and relationship of symptoms to eating, excessive alcohol intake, abdominal pain, weight loss, anxiety, palpitations, tremor, lifelong history of constipation, immunocompromised person, features of systemic disease, systemic illness and rashes.

Investigations: Bloods - FBC, U&Es, LFTs, Calcium, Vitamin B12 and red blood cell folate, Iron status, TFTs, ESR, CRP, test for coeliac disease. Consider Ca125 if there are features of ovarian cancer. Consider HIV serology in immunodeficiency is suspected. Consider sending stool sample for routine microbiological investigation and examination for ova, cysts and parasites. C-diff testing. Faecal calprotectin testing. Testing for blood in faeces.

Perform an abdominal examination. Do a digital rectal examination.

Refer using cancer pathway if suspected colorectal cancer. Refer for further assessment and management if history/examination/investigation suggests coeliac disease, Crohn's disease, ulcerative colitis, bile acid diarrhoea, microscopic colitis or malabsorption, person <40 does not have typical symptoms, or the diagnosis is uncertain.