AKT · Gastroenterology/Colon & rectum

Infectious diarrhoea & gastroenteritis

Acute GI infection — viral (norovirus/rotavirus), bacterial, or protozoal

Overview

Acute infective diarrhoea ± vomiting, usually viral (norovirus, rotavirus in children) and self-limiting; bacterial (Campylobacter — commonest UK bacterial cause, Salmonella, Shigella, E. coli, C. difficile) and protozoal (Giardia, Cryptosporidium, Entamoeba) in specific contexts. Management is rehydration; antibiotics are reserved for specific pathogens/severe disease; the priorities are hydration, public-health notification and recognising the dysentery/HUS/typhoid red flags.

Recognise

Acute diarrhoea ± vomiting, cramps, fever; watery (viral/toxin) vs BLOODY (dysentery — invasive bacteria/amoebae)
Clues: norovirus (winter outbreaks, projectile vomiting), Campylobacter (undercooked poultry, can trigger Guillain-Barré/reactive arthritis), Giardia (travel, prolonged, malabsorptive, flatulence), Salmonella/typhoid (travel, fever)
Dehydration is the main risk (esp. extremes of age)

Red flags

Severe dehydration/shock; bloody diarrhoea (dysentery); EHEC O157 → HUS (no antibiotics); enteric fever (typhoid — travel, fever, relative bradycardia)
Immunocompromised, recent hospital/antibiotics (C. diff), or systemic sepsis

Differentials & how to tell them apart

C. difficile colitisrecent antibiotics, raised WCC, toxin-positive

Inflammatory bowel diseasechronic relapsing, raised calprotectin

Appendicitis/surgical abdomenlocalised peritonism rather than diffuse diarrhoeal illness

Giardiasisprolonged, malabsorptive, travel — stool antigen/microscopy

Investigations

Usually clinical. Stool culture/PCR if bloody, severe, prolonged (>7 days), recent travel, immunocompromised, or public-health relevant; C. diff testing if antibiotic-associated. U&Es/FBC if dehydrated; ova/cysts/parasites for persistent/travel diarrhoea.

Management

Rehydration (oral/IV); targeted antibiotics only for specific pathogens

1Rehydrate (oral rehydration solution or IV); most viral/bacterial gastroenteritis is self-limiting and needs NO antibiotics. Hygiene/isolation; advise off work/school until 48 h symptom-free.Gate: Do NOT give antibiotics for simple gastroenteritis or suspected EHEC O157 (HUS risk); reserve antibiotics for specific pathogens (severe Campylobacter, Giardia/amoebae with metronidazole, typhoid) — and avoid antimotility agents in bloody diarrhoea/C. diff
2Notify relevant pathogens to public health; investigate persistent/travel diarrhoea (parasites); manage complications (HUS, reactive arthritis, Guillain-Barré after Campylobacter).

Oral rehydration / IV fluids — the mainstay — replace losses

Targeted antibiotics ONLY for specific cases — e.g. severe Campylobacter (clarithromycin), Giardia/amoebae (metronidazole), typhoid; NOT for simple/EHEC

Avoid antimotility agents in dysentery/C. diff — loperamide risks toxic megacolon/HUS

Key points

Rehydrate first; most need no antibiotics. Campylobacter (chicken; GBS/reactive arthritis), norovirus (outbreaks), Giardia (travel, malabsorptive), EHEC (no antibiotics → HUS). Bloody diarrhoea = invasive/dysentery.

Monitor & prognosis

Hydration; stool results; complications.

Usually self-limiting.

Source: NICE CKS Gastroenteritis; UKHSA