infectious diarrhoea
in review
4 min read
Updated 2026-09-29
infectious diarrhoea
Most acute diarrhoea is viral and self-limited — rehydrate, no stool testing, no antibiotics. Test (stool culture/multiplex PCR) if fever, blood, severe dehydration, sepsis, immunocompromise, >7 days, or outbreak; C. difficile if recent antibiotics or hospitalisation; ova and parasites if >14 days, travel, or immunocompromise. Empiric antibiotics only for dysentery with fever, severe traveller’s diarrhoea, or sick immunocompromised hosts — azithromycin preferred. Never give antibiotics or antimotility agents for suspected STEC (HUS risk).
do not miss
- STEC (O157:H7): bloody diarrhoea, little fever → no antibiotics, monitor CBC and creatinine for HUS (days 5–10)
- enteric fever presents with fever and constitutional symptoms, often without diarrhoea — blood cultures (see fever in the returned traveller)
- C. difficile in any patient with recent antibiotics — see Clostridioides difficile infection
local antibiogram
Campylobacter and Shigella (especially XDR Shigella in GBMSM) are frequently fluoroquinolone-resistant; South and Southeast Asian travel → azithromycin, not ciprofloxacin.
who to test
| test | indication |
|---|---|
| stool culture / multiplex GI PCR | fever, bloody or mucoid stool, severe pain, dehydration, sepsis, immunocompromised, symptoms >7 days, outbreak, food handler/healthcare worker |
| C. difficile | antibiotics in past 3 months, hospitalisation, ≥3 unformed stools/24 h |
| ova and parasites ×3 / parasite PCR | diarrhoea >14 days, travel, immigrants, GBMSM, daycare exposure, immunocompromised |
| blood cultures | fever/sepsis, suspected enteric fever, immunocompromised, age >50 with suspected Salmonella |
| Shiga toxin testing | all bloody diarrhoea |
management
- oral rehydration first; IV if severe dehydration
- loperamide acceptable in adults with watery, non-bloody, afebrile diarrhoea — avoid with fever, blood, or suspected STEC/C. difficile
- empiric antibiotics only for: febrile dysentery (suspected Shigella), severe traveller’s diarrhoea, immunocompromised with severe illness, sepsis
- azithromycin 1 g PO × 1 (or 500 mg daily × 3 days) — preferred, including for dysentery and Asia travel
- ciprofloxacin 750 mg × 1 or 500 mg BID × 3 days — where susceptibility likely
- rifaximin — non-invasive (watery) traveller’s diarrhoea only
pathogen-directed therapy
| pathogen | clues | treatment |
|---|---|---|
| Campylobacter | undercooked poultry; fever, bloody diarrhoea, pseudoappendicitis | azithromycin if severe/immunocompromised; → Guillain–Barré, reactive arthritis |
| Shigella | low inoculum, person-to-person (GBMSM, daycare); dysentery | treat — azithromycin, ciprofloxacin, or ceftriaxone per susceptibility; XDR → ID |
| non-typhoidal Salmonella | poultry, eggs, reptiles | no antibiotics unless age <3 months or >50 with atherosclerosis/prosthetic valve/endovascular graft, immunocompromised, severe/bacteraemic → ciprofloxacin, ceftriaxone, or azithromycin |
| STEC (O157:H7) | ground beef, produce; bloody diarrhoea, minimal fever | no antibiotics, no antimotility; monitor for HUS |
| Yersinia | pork, milk; mesenteric adenitis mimicking appendicitis; iron overload (deferoxamine) | usually none; severe → ciprofloxacin or TMP-SMX |
| Vibrio cholerae | endemic travel, rice-water stool | aggressive rehydration; doxycycline 300 mg × 1 (or azithromycin) |
| Vibrio parahaemolyticus | raw shellfish | supportive |
| norovirus | outbreaks, vomiting predominant | supportive; contact precautions, soap and water |
| Giardia | camping/untreated water, daycare; bloating, steatorrhoea, prolonged | metronidazole 500 mg TID × 5–7 days or tinidazole 2 g × 1 |
| Cryptosporidium | water/pools, animals; severe chronic in advanced HIV | nitazoxanide; ART in HIV |
| Cyclospora | imported produce; prolonged watery diarrhoea, fatigue | TMP-SMX DS BID × 7–10 days |
| Entamoeba histolytica | travel; dysentery, liver abscess | metronidazole → paromomycin (luminal) |
traveller’s diarrhoea
- mostly enterotoxigenic E. coli; self-limited 3–5 days
- mild: hydration ± loperamide; moderate: loperamide ± single-dose azithromycin; severe or dysentery: azithromycin
- prophylactic antibiotics not recommended for most travellers (resistance, ESBL colonisation)
- persistent (>14 days) → Giardia, other parasites, post-infectious IBS, coeliac, IBD
complications
- HUS (STEC): microangiopathic haemolytic anaemia + thrombocytopaenia + AKI, typically days 5–10 after diarrhoea onset
- Guillain–Barré (Campylobacter); reactive arthritis (Campylobacter, Shigella, Salmonella, Yersinia)
- post-infectious IBS; lactose intolerance
- endovascular infection with non-typhoidal Salmonella bacteraemia in older adults → image aorta if persistent bacteraemia
traps
- antibiotics for bloody diarrhoea before STEC is excluded
- ciprofloxacin for dysentery acquired in Asia
- treating uncomplicated non-typhoidal Salmonella (prolongs carriage)
- forgetting C. difficile testing in a patient with recent antibiotics
- a single negative O&P excluding parasites