Back to top

Infectious Colitis

The presence of blood or mucous in stools, significant abdominal pain, fever and the presence of abdominal tenderness on examination would usually lead one to differentiate simple infectious gastroenteritis from the more complicated colitis. Most cases are caused by bacterial pathogens that invade the gut lining or produce mucosal inflammation. Common pathogens include C diff, Salmonella, Campylobacter, Shigella, E Coli, Yersinia, occasionally amoebic and viral infections (e.g. CMV).


  • Nausea, vomiting, abdo pain, fevers, diarrhoea, – watery/bloody.

  • Recent antibiotic use.

  • Recent inpatient/long term facility stay.

  • Travel history.


Look for signs of toxicity, sepsis and dehydration.

Assessing dehydration:

  • Mild dehydration: anorexia, nausea, light-headedness, postural hypotension; usually no signs.

  • Moderate dehydration: tiredness, dizziness, muscle cramps, dry tongue or sunken eyes, reduced skin elasticity, postural hypotension, tachycardia, oliguria.

  • Severe dehydration: profound apathy, weakness, confusion (leading to coma), shock, tachycardia, marked peripheral vasoconstriction, systolic blood pressure less than 90 mm Hg, oliguria or anuria.

Assessing dehydration in children:


  • Stool culture including for C diff.

  • For immunocompromised or systemically unwell patients FBC, EUC, lactate, blood cultures – raised WBC, electrolyte disturbance, renal failure associated with dehydration, poor tissue perfusion.

  • Consider imaging (X-ray or CT) especially in elderly, immunosupressed, septic.


  • Rehydrate with oral or IV solution keeping close eye on electrolytes and replace as required.

  • Antibiotic treatment generally only indicated when bacterial infection is severe eg signs dehydration or systemic toxicity. Empirical therapy may be considered in immunocompromised patients. In infants bacterial gastroenteritis is also often treated more aggressively due to risk of severe sepsis.

  • Please consult your local antibiotic guidelines.

  • Empirical treatment:

    • Ciprofloxacin 500mg (12.5mg/kg) PO 12 hourly for 3 days

    • Or Norfloxacin 400mg (10mg/kg) PO 12 hourly for 3 days

    • If quinolone resistance suspected (eg S & E Asia) – Azithromycin 500mg (10mg/kg) PO daily for 3 days

    • If oral not feasible – Ceftriaxone 2g (50mg/kg) IV daily for 3 days.

  • Low risk patients with mild to moderate illness can be discharged with GP follow up while awaiting formal culture results. Emphasise the importance of fluid and electrolyte intake, when to return and hand washing.

  • Issue patient with relevant patient factsheet:


  • Antibiotic therapy not recommended in children with suspected enterohaemorrhagic E coli due to increased risk of haemolytic uraemic syndrome (HUS).

  • May need to notify your Public Health Unit particularly if 2 or more cases of food bourne diarrhoea present.

Further References and Resources

© Agency for Clinical Innovation 2023