Try to assess whether this has an infectious basis.
Initial history is important. Include severity of diarrhoea, fever, passage of bloody stool, any upper GI symptoms, history of recent surgery, radiation, drugs (especially antibiotics) and overseas travel or infectious contacts. Also record the food eaten and occupation. Ask about similar symptoms in relatives or friends.
An urgent erect and supine abdominal X-ray may be required.
CBC + diff, urea, creatinine, Na, K.
Blood cultures if patient is febrile or has been abroad.
Stool examination - a freshly collected stool specimen should be examined and the specific requests should reflect the clinical setting:
Microscopy: Parasites (microsporidia, cryptosporidia in immunosuppressed).
Bacteria: Request cultures for Salmonella, Shigella, Yersinia, Aeromonas, Campylobacter and Plesiomonas. (Toxic forms of E. coli can be cultured on request).
Viruses: Norovirus. Rotavirus is looked for in paediatric samples and other viruses will be tested on request.
Cl. difficile toxin assay: Available on liquid stool if appropriate. Culture not routinely done.
Parasites: 3 faecal samples on separate days in PVA fixative for parasite examination.
Giardia antigen: Request specifically for this antigen if required. Fresh specimen needed.
Acute diarrhoea is not an indication for colonoscopy.
Enteric isolation procedures required if infection suspected (contact Infection Control).
IV fluids may be required. Remember faecal losses of electrolytes may be very high. 100-120 mmol sodium and 5-15 mmol potassium may be lost per litre of stool. An adult may lose more than 2-3 L of fluid per day.
Avoid constipating drugs (especially in children) as these may prolong symptoms.
Antimicrobials are not indicated for the majority of infective diarrhoeas.
Specific infections:
Salmonella/Shigella/Campylobacter are usually self-limiting and antibiotics should only be used when illness is severe with systemic upset/septicaemia. These are notifiable diseases.
Pseudomembranous colitis; always suspect when antibiotics have been taken within last few weeks. Sigmoidoscopy may sometimes be diagnostic but is usually unnecessary. If suspected, check for Clostridium difficile toxin and treat. Treatment of choice metronidazole 400 mg TDS PO 7-10 days. Is effective for relapse or recurrence. Alternative - vancomycin 125 mg PO QID.
HIV - always suspect in at risk populations. Almost all have some gut manifestation either directly due to HIV or secondary to CMV, Cryptosporidia, Giardia, Mycobacterium avium intracellulare, Kaposi's sarcoma, lymphoma etc. (see HIV and AIDS).
Toxic megacolon (diameter >5.5 cm) should be considered in any person with inflammatory bowel disease, systemic toxicity and increasing diarrhoea (can paradoxically be reduced). Requires CT scan abdomen and urgent review with early gastroenterology and surgical referral.
Steroids are drugs of choice in acute situation. Give IV hydrocortisone 100 mg q6h then prednisone 30-60 mg/day PO.
Sulphasalazine 1 g QID PO or mesalazine 1 g QID PO, may be of benefit pending diagnosis in less severe attacks.
IV fluids, nutrition and antibiotics may be needed. Always consider other causes of diarrhoea and/or bleeding.
Patients on immunosuppressive treatment - steroids, azathioprine, TNF-alpha inhibitors, etc., are at increased risk of infection.
Patients hospitalized with active inflammatory bowel disease should receive thromboprophylaxis with LMWH unless contraindicated. Discuss with Consultant if uncertain.
Note: Other causes of diarrhoea include carcinoma, ischaemic colitis, diverticulitis, and constipation with overflow. Laxative abuse may cause dehydration, muscular weakness and hypokalaemia. Consider this in chronic diarrhoea.