Antimicrobial Stewardship and Resistance — Written Clinical Reasoning

SAQ 1 — Integrated Management of Severe Clostridioides difficile Infection (20 marks, 30 minutes)

Prompt: Outline your integrated management plan for this patient with severe recurrent Clostridioides difficile infection, including: (a) the severity stratification you are applying and its implications for therapy, with the exact first-line drug, dose, route and duration; (b) the additional pharmacological therapy you would consider given her recurrence risk; (c) the supportive and infection-control measures; (d) the surgical and microbiological escalation pathway if she deteriorates; (e) the prevention of further recurrence; and (f) the high-yield exam traps in CDI management. ^[1]

Model Answer

(a) Severity stratification and first-line therapy (4 marks): ^[1]

This patient has severe and fulminant Clostridioides difficile infection. Severity is defined by the IDSA/SHEA criteria: a white cell count of 15 x 10^9 per litre or above (she is 26) and/or a creatinine 1.5 times the baseline or above (her creatinine has risen from 78 to 165, more than double) define severe disease; fulminant disease adds hypotension, shock, ileus or toxic megacolon. She meets the fulminant criteria because of her hypotension (blood pressure 92/58) and clinical instability, on top of severe biochemical markers ^[2]. The most appropriate first-line therapy for fulminant CDI is oral vancomycin 500 mg four times daily PLUS intravenous metronidazole 500 mg every 8 hours, continued until the patient is improving and the diarrhoea is settling (typically 10 to 14 days). The reason for the higher vancomycin dose (500 mg rather than 125 mg) in fulminant disease is to achieve high intraluminal colonic concentrations in the face of an inflamed, oedematous mucosa and reduced gut motility; the addition of IV metronidazole provides systemic cover because oral vancomycin is not absorbed and may not reach the colon in adequate concentration if there is an ileus. Metronidazole is no longer first-line for any non-fulminant adult CDI (replaced by fidaxomicin and oral vancomycin for non-severe and severe disease), but it retains a role as an IV adjunct in fulminant disease.

(b) Additional pharmacological therapy for recurrence prevention (3 marks): ^[1]

This patient is at high risk of recurrence because she is over 65, has severe CDI, has had a prior CDI episode within the past year, and is immunocompromised by her acute illness. The MODIFY I and MODIFY II trials demonstrated that a single 10 mg/kg intravenous infusion of bezlotoxumab (a human monoclonal antibody against toxin B), given WITH standard antibiotic therapy, reduced 12-week recurrence from 26.6 to 16.5 per cent in the pooled analysis, with the greatest benefit in high-risk patients ^[4]. I would administer bezlotoxumab on day 1 of therapy. I would NOT use faecal microbiota transplantation in the acute fulminant episode — it is reserved for second or subsequent recurrence after clinical stabilisation, not for primary treatment of fulminant disease. I would not switch to fidaxomicin at this acute stage because fulminant disease with shock warrants the high-dose vancomycin plus metronidazole combination; fidaxomicin is preferred for non-fulminant severe CDI and for recurrence, but the evidence in fulminant shock is weaker. Once she stabilises, I would consider a transition to fidaxomicin or a vancomycin taper to complete the course.

(c) Supportive and infection-control measures (3 marks): ^[1]

Supportive measures include intravenous fluid resuscitation (crystalloid, guided by perfusion and urine output) for her hypovolaemia and acute kidney injury, electrolyte correction (potassium and magnesium losses through diarrhoea), and avoidance of antimotility agents (loperamide is contraindicated in acute severe CDI because it precipitates toxic megacolon). I would stop the inciting ceftriaxone immediately. I would not give probiotics routinely — the evidence is modest and the patient is acutely ill. Infection control requires single-room isolation with contact precautions (gown and gloves for all contact), dedicated equipment (stethoscope, blood pressure cuff, thermometer), hand hygiene with soap and water (not alcohol-based hand rub, which is less effective against C. difficile spores) before and after every contact, and environmental cleaning with a sporicidal agent (hypochlorite-based bleach). I would notify the infection-control team for surveillance and contact tracing if there are other cases on the ward. ^[1]

(d) Surgical and microbiological escalation (3 marks): ^[1]

I would request an urgent surgical review because fulminant CDI can progress to toxic megacolon (caecal diameter above 6 cm with systemic toxicity), colonic perforation, or refractory septic shock — all of which are indications for subtotal colectomy, which is life-saving in refractory fulminant CDI. The clinical signs of deterioration that mandate surgical review are: worsening abdominal distension and tenderness, haemodynamic deterioration despite maximal medical therapy, rising lactate, falling platelet count (suggesting DIC), and radiological evidence of toxic megacolon or perforation on abdominal CT or X-ray. I would order a CT abdomen with contrast if there is any doubt about toxic megacolon, perforation or an alternative diagnosis. Microbiologically, I would send the isolate for ribotyping and binary toxin testing to identify the NAP1/BI/027 hypervirulent strain, which carries higher morbidity, mortality and recurrence ^[2], although the result does not change the acute management. I would involve the infectious diseases team from the outset.

(e) Prevention of further recurrence (3 marks): ^[1]

Recurrence is the central long-term challenge: after one recurrence the risk of a further recurrence is 40 to 65 per cent. The prevention strategy has several layers. First, minimise further antibiotic exposure — every additional antibiotic course predisposes to recurrence, and stewardship is itself preventive. Second, if she recurs, treat with fidaxomicin (which has a recurrence advantage over vancomycin from the Louie trial, 15 versus 25 per cent ^[6]) or a tapered-and-pulsed oral vancomycin course. Third, for a second or subsequent recurrence, arrange faecal microbiota transplantation, which achieved 94 per cent cure after one or two infusions in the van Nood randomised trial ^[5]. Fourth, bezlotoxumab given in the acute episode reduces recurrence for the next 12 weeks. Fifth, there is emerging evidence for the extending-pulsed fidaxomicin regimen (every-other-day dosing after an initial course) for multiply-recurrent CDI. I would give her written information about CDI, counsel her to seek early review for any recurrence of diarrhoea, and communicate the plan to her general practitioner.

(f) High-yield exam traps (4 marks): ^[1]

The traps are: (1) metronidazole as first-line — metronidazole is no longer first-line for any adult CDI; use fidaxomicin or oral vancomycin for non-fulminant disease, and reserve IV metronidazole as an adjunct in fulminant disease; (2) the test of cure — do NOT repeat the toxin assay after clinical resolution; toxin persists for weeks and treating an asymptomatic patient with a positive result is futile and counterproductive; clinical resolution is the endpoint; (3) antimotility agents in acute severe disease — loperamide is contraindicated in severe CDI because it precipitates toxic megacolon; (4) alcohol-based hand rub for C. difficile — soap and water is required because alcohol does not kill spores; (5) under-dosing oral vancomycin in fulminant disease — the 500 mg four times daily dose is required in fulminant disease, not the 125 mg dose used for non-severe and non-fulminant severe CDI; (6) missing toxic megacolon — any clinical deterioration in a patient with severe CDI mandates a surgical review and abdominal imaging, because subtotal colectomy is life-saving in refractory fulminant disease; (7) not addressing recurrence prevention — bezlotoxumab, fidaxomicin, and faecal microbiota transplantation all have roles in patients at high recurrence risk, and a patient with severe recurrent CDI deserves a documented recurrence-prevention plan. ^[1]