Acute & Chronic Diarrhoea — classification, red flags, dehydration, and C. difficile management

(a) Classification and severity

This is acute (under 14 days) infectious diarrhoea, by mechanism inflammatory/secretory, and the presentation is highly suggestive of Clostridioides difficile infection (CDI): recent clindamycin exposure (a classic high-risk antibiotic), care-home residence, age over 65, profuse watery diarrhoea with cramps and fever.^[4]

Severity (two parallel scales):

• WHO/IMCI dehydration — she has SEVERE dehydration: two or more of lethargy/confusion, sunken eyes, unable/unlikely to drink, skin pinch going back very slowly (Plan C = IV resuscitation).^[1]
• C. difficile severity (SHEA/IDSA 2021) — severe (WBC over 15 x 10^9/L and creatinine over 1.5 mg/dL/133 micromol/L relative to baseline). She is not fulminant (no hypotension refractory to fluids, ileus or megacolon yet).^[4]

She also has acute kidney injury (KDIGO stage 2) from pre-renal dehydration, hypokalaemia (K 3.0) and mild hyponatraemia from gut loss.

(b) Immediate investigations

• Stool — send for C. difficile testing using a two-step or algorithmic approach: GDH (glutamate dehydrogenase) plus toxin A/B EIA, with NAAT (PCR) as a reflex arbiter, or a NAAT plus toxin strategy. Never test formed stool. Also send stool culture (Salmonella, Shigella, Campylobacter, E. coli O157) and ova/cysts/parasites (Giardia, Cryptosporidium, Entamoeba), and faecal calprotectin/lactoferrin as inflammatory markers, because the differential includes other infective colitides.^[1][4]
• Bloods — FBC, U&E (track creatinine and potassium), venous bicarbonate and lactate (assess acidosis/sepsis), CRP, albumin, glucose; blood cultures (fever and possible bacteraemia); group and save.
• ECG — hypokalaemia risk.
• Imaging — plain abdominal X-ray to look for colonic dilatation (toxic megacolon) or thumbprinting; CT abdomen if tenderness worsens or to exclude perforation/ischaemia.
• Lower GI endoscopy (flexi-sig) only if stool testing is negative but suspicion remains — to look for pseudomembranes (pseudomembranous colitis); avoid in unstable patients (perforation risk).

(c) Time-critical management (drug, dose, route, rationale)

1. Resuscitate — WHO Plan C / ABC. IV access, 0.9% sodium chloride or balanced crystalloid (Ringer's lactate/Hartmann's) 10-20 mL/kg boluses titrated to perfusion and blood pressure, then maintenance with potassium replacement guided by serial U&E (correct K to over 4.0 mmol/L; ~40 mmol per litre of fluid, cautious if AKI). Insert a urinary catheter to monitor output. Correct acidosis with fluid; avoid premature bicarbonate.^[1]
2. Stop the offending antibiotic — discontinue clindamycin and review all antimicrobials and a PPI (an independent CDI risk factor — deprescribe if not essential).
3. Specific anti-C. difficile therapy (SHEA/IDSA 2021): because she meets severe criteria, give fidaxomicin 200 mg orally twice daily for 10 days (preferred); alternative vancomycin 125 mg orally four times daily for 10 days. (Metronidazole 400 mg TDS is now reserved only when fidaxomicin and vancomycin are unavailable.) If she were fulminant (ileus, hypotension, megacolon), escalate to vancomycin 500 mg orally/NG four times daily PLUS IV metronidazole 500 mg TDS and obtain urgent surgical review for possible colectomy.^[4]
4. Symptomatic — avoid loperamide/antimotility (risk of toxic megacolon in inflammatory/C. difficile diarrhoea); analgesia with paracetamol; antiemetics if vomiting; NBM only if peritonism or for procedures.
5. Electrolyte and renal — repeat U&E every 6-12 h; nephrology input if AKI worsens; adjust all renally-cleared drugs.

(d) Complications and public-health measures

Complications to anticipate: toxic megacolon and perforation (monitor abdominal girth, repeat X-ray, surgical review), refractory hypovolaemic shock, AKI progression, electrolyte disturbance (hypokalaemia, hyponatraemia), hypoalbuminaemia and ascites/oedema from a protein-losing enteropathy, recurrence (15-30 percent after a first episode; multiple recurrences managed with vancomycin taper/pulse, fidaxomicin or faecal microbiota transplant), bacteraemia in the immunocompromised, and post-infectious IBS.^[4]

Public-health and infection-control measures:

• Isolate in a single room with contact precautions for the duration of diarrhoea; dedicated equipment.
• Hand hygiene with soap and water — alcohol hand-rub does NOT kill C. difficile spores.
• Environmental cleaning with a sporicidal agent (e.g. chlorine-releasing/bleach 1000 ppm).
• Notify the local health protection unit / Integrated Disease Surveillance Programme where required.
• Exclusion: care-home staff, food-handlers, healthcare workers and the patient herself should not return to group/sensitive settings until 48 h after the first normal stool; longer for specific organisms.
• Antibiotic stewardship review — audit and restrict clindamycin, fluoroquinolones and broad-spectrum cephalosporins; reassess the original cellulitis antibiotic choice.