Healthcare-Associated Infections — Written Clinical Reasoning

SAQ 1 — Integrated Management of Catheter-Related Bloodstream Infection with Concurrent Ventilator-Associated Pneumonia (20 marks, 30 minutes)

Prompt: Outline your integrated management plan for this patient with Pseudomonas aeruginosa catheter-related bloodstream infection and concurrent ventilator-associated pneumonia, including: (a) the interpretation of the culture results and the significance of the differential time to positivity; (b) the management of the central venous catheter; (c) the empiric and targeted antibiotic strategy, including agent, dose, route and duration; (d) the ventilator management and VAP prevention bundle; (e) the search for metastatic infection and complications; and (f) the prevention lessons and stewardship review. [1]

Model Answer

(a) Interpretation of culture results and differential time to positivity (3 marks): [1]

This patient has Pseudomonas aeruginosa catheter-related bloodstream infection (CRBSI) with concurrent ventilator-associated pneumonia (VAP). The key diagnostic findings are: paired blood cultures (peripheral and central) both growing the same organism (Pseudomonas aeruginosa), with the central line culture turning positive more than 120 minutes before the peripheral culture. This differential time to positivity (DTP) above 120 minutes strongly supports the central venous catheter as the source of the bacteraemia — the higher bacterial inoculum in the blood drawn through the infected line reaches the detection threshold sooner. The concurrent growth of the same Pseudomonas organism from the endotracheal aspirate, with the same sensitivity pattern, confirms VAP. Whether the patient has bacteraemia from TWO sources (the line and the lungs) or whether one is seeding the other is clinically important but does not change the immediate management — both foci must be treated. The negative urine culture rules out a urinary source. The clean surgical wound and absence of diarrhoea exclude SSI and C. difficile infection [3].

(b) Management of the central venous catheter (3 marks): [1]

The central venous catheter must be removed. Pseudomonas aeruginosa is NOT an organism for which catheter salvage should be attempted — like Staphylococcus aureus and Candida, Pseudomonas forms resilient biofilms on catheter surfaces that are extremely difficult to eradicate with systemic antibiotics alone, and attempted salvage is associated with high rates of persistent bacteraemia, relapse, and metastatic infection. The catheter should be removed, the tip sent for semi-quantitative culture (Maki roll-plate method), and a new central line inserted at a different site if ongoing central access is needed (preferably the subclavian vein to minimise the infection risk, if there are no contraindications) [3] [2]. A guidewire exchange of the infected catheter is contraindicated — the new catheter is placed through the infected track. I would document the removal, the tip culture result, and the indication for the new line. If central venous access is no longer needed (the patient can be managed with peripheral access), no replacement is necessary.

(c) Empiric and targeted antibiotic strategy (4 marks): [1]

Because cultures were obtained BEFORE starting antibiotics, and the organism and sensitivities are known from the initial cultures, I do not need to start broad empiric therapy — I can start targeted therapy directly. The organism is Pseudomonas aeruginosa; the appropriate agent is an anti-pseudomonal beta-lactam to which the isolate is susceptible — options include piperacillin-tazobactam 4.5 g IV every 6 hours, ceftazidime 2 g IV every 8 hours, cefepime 2 g IV every 8 hours, or meropenem 1 g IV every 8 hours (if the isolate is a carbapenemase producer, which is unlikely here without specific risk factors, therapy must be guided by susceptibility testing). I would NOT add vancomycin — there is no evidence of MRSA or other Gram-positive infection, and the blood cultures grew only Pseudomonas. I would NOT add an aminoglycoside routinely — combination therapy with an aminoglycoside does not improve outcomes in Pseudomonas bacteraemia and adds nephrotoxicity, which is particularly undesirable in a critically ill postoperative patient who may already have or be at risk of acute kidney injury. [1]

The duration of therapy is determined by the bloodstream infection and the lung infection. For uncomplicated Pseudomonas CRBSI after catheter removal, the duration is 7 to 14 days from the first negative blood culture. For VAP, the duration is typically 7 days with good clinical response. Since this patient has both, I would treat for 14 days from the first negative blood culture (or from the start of appropriate therapy if cultures clear rapidly), monitoring clinical response (fever, white cell count, oxygenation, inflammatory markers) and repeating blood cultures every 48 to 72 hours until clearance. If blood cultures remain positive beyond 72 hours despite catheter removal and appropriate therapy, I would search for metastatic infection and consider a longer duration [3].

(d) Ventilator management and VAP prevention bundle (3 marks): [1]

The ventilator management focuses on treating the VAP and preventing further ventilator-associated complications. The patient should continue on appropriate respiratory support, with daily assessment for readiness to extubate. The VAP prevention bundle should be applied [4]:

• Head of bed elevation to 30 to 45 degrees to prevent further microaspiration.
• Daily sedation interruption with a spontaneous breathing trial to minimise the duration of ventilation and identify readiness for extubation as early as possible.
• Oral chlorhexidine mouthwash or gel.
• Subglottic secretion drainage if the endotracheal tube has a dedicated suction port (or consider exchanging to a subglottic suction tube at the next opportunity, weighing the risk of tube exchange against the benefit).
• Peptic ulcer prophylaxis and DVT prophylaxis as part of the overall ICU care bundle.
• Daily review of the need for ongoing intubation — the single most effective VAP prevention measure is extubation as soon as the patient can safely be weaned. [1]

I would also ensure the ventilator circuit is managed appropriately (change only if visibly soiled or malfunctioning — routine circuit changes do not prevent VAP and may increase it). [1]

(e) Search for metastatic infection and complications (3 marks): [1]

Pseudomonas aeruginosa bacteraemia can cause metastatic infection, though less commonly than Staphylococcus aureus. I would monitor for: [1]

• Persistent or relapsing bacteraemia — repeat blood cultures every 48 to 72 hours until clearance. If bacteraemia persists beyond 72 hours despite catheter removal and appropriate therapy, I would search for a deep source: echocardiography to exclude endocarditis (particularly right-sided endocarditis in a patient with bacteraemia and an intravascular device), CT imaging to identify occult abscesses (psoas, hepatic, splenic, pulmonary), and consideration of metastatic seeding to skin (ecthyma gangrenosum in immunocompromised patients).
• Septic emboli — particularly to the lungs (new infiltrates, cavitation, necrotising pneumonia) in the setting of right-sided endocarditis.
• Acute kidney injury — Pseudomonas sepsis and aminoglycoside therapy (if used) both carry nephrotoxicity risk.
• Ongoing intra-abdominal source — given the perforated diverticulum, I would have a low threshold for repeat CT imaging if the patient does not improve, to exclude a residual collection or leak requiring drainage. [1]

(f) Prevention lessons and stewardship review (4 marks): [1]

The prevention lessons from this case are several. First, the central line had been in situ for 7 days — was it still needed? Every central line should have a documented daily indication, and the single most effective prevention measure is removal as soon as it is no longer needed. I would audit the documentation of the daily line indication on this patient and on all ICU patients. [1]

Second, was the central line insertion performed with the full barrier precautions bundle — sterile gown, gloves, cap, full-body drape, chlorhexidine skin preparation, and avoidance of the femoral site? The Pronovost Michigan study demonstrated that reliable implementation of this bundle reduced CLABSI by up to 66 per cent [1]. I would review the insertion documentation and the unit's bundle adherence data.

Third, was the ventilator bundle applied reliably — head of bed elevation, daily sedation interruption, oral chlorhexidine, and subglottic secretion drainage? VAP is preventable with reliable bundle implementation [4].

Fourth, the stewardship review: the patient received 5 days of piperacillin-tazobactam postoperatively. Was this appropriate (perforated diverticulum with peritonitis does require broad-spectrum cover initially), and was it de-escalated and stopped promptly when cultures returned? The broad-spectrum antibiotic exposure predisposes to subsequent multidrug-resistant colonisation and infection (this patient's Pseudomonas may have been selected by the preceding antibiotic exposure), and to Clostridioides difficile infection. I would ensure the antibiotic course is reviewed daily, narrowed to the narrowest effective agent, and stopped as soon as clinically indicated [6].

Finally, I would communicate the management plan, the infection control measures, and the prevention lessons to the treating team, the nursing staff, and the infection control team, and I would document the case for the unit's HAI surveillance and quality improvement programme. [1]

SAQ 2 — Outbreak of Carbapenem-Resistant Enterobacteriaceae on a Surgical Ward (10 marks)

Prompt: Over a 4-week period, three patients on a 30-bed surgical ward are found to have rectal surveillance swabs positive for carbapenemase-producing Klebsiella pneumoniae (NDM-type). None of the three had known CRE colonisation on admission. Outline: (a) your immediate infection control response to the outbreak; (b) the screening strategy for ward contacts; (c) the environmental investigation; (d) the antimicrobial stewardship dimension; and (e) the communication plan with patients, staff, and hospital administration. [1]

Model Answer

(a) Immediate infection control response (2 marks): [1]

This is a cluster of healthcare-acquired CRE colonisation suggesting cross-transmission on the ward. The immediate response is: place all three patients in single-room isolation with contact precautions (gown, gloves, dedicated equipment, soap-and-water hand hygiene before and after every contact), notify the infection control team and the clinical microbiologist immediately, and convene an outbreak investigation meeting. I would review the ward's hand hygiene adherence data, the cleaning and disinfection practices, and the equipment sharing practices (shared glucometers, shared thermometers, shared BP cuffs, shared ultrasound machines). The principle is that CRE spreads on the hands of healthcare workers and on shared equipment, and the control measures must interrupt both routes [7].

(b) Screening strategy for ward contacts (2 marks): [1]

I would perform rectal surveillance swabs on all patients who shared the ward with the three index cases during the exposure period (the 4 weeks of the outbreak). Patients who had direct bedside contact (adjacent beds, shared nursing care, shared bathrooms) are the highest priority. I would screen on the day of the investigation and repeat at 48 to 72 hours (to account for the incubation period and the sensitivity of a single swab). Patients found to be colonised would be isolated and managed with contact precautions. I would maintain surveillance on the ward (admission screening for all new admissions and weekly surveillance swabs for all current patients) until no new cases are identified for a defined period (typically 2 to 4 weeks), and I would flag all colonised patients in the hospital electronic record for isolation on future admissions — CRE gut carriage is prolonged and the patient remains a transmission risk indefinitely [7].

(c) Environmental investigation (2 marks): [1]

CRE can persist on inanimate surfaces for prolonged periods, and environmental contamination is a recognised reservoir for cross-transmission. I would commission an environmental investigation including: enhanced terminal cleaning of all affected patient rooms and shared areas with a sporicidal or appropriate disinfectant (hypochlorite-based); targeted environmental cultures of high-touch surfaces (bed rails, call buttons, bedside tables, shared equipment, sinks, and especially the sink traps and drain pipes — hospital sinks are a recognised reservoir for Gram-negative organisms including CRE); and review of the cleaning protocols and cleaning adherence. If the environmental cultures identify a contaminated sink or shared equipment, the source must be addressed (replacement of sink traps, dedication of equipment to individual patients, or removal of the contaminated item). Molecular typing (whole-genome sequencing or pulsed-field gel electrophoresis) of the three isolates would determine whether they are clonally related (supporting cross-transmission from a common source or patient-to-patient spread) or unrelated (suggesting independent acquisition). [1]

(d) Antimicrobial stewardship dimension (2 marks): [1]

CRE colonisation and infection are driven by antibiotic selection pressure — carbapenem exposure and broad-spectrum cephalosporin exposure select for carbapenemase-producing organisms. I would review the antibiotic prescribing on the ward: what proportion of patients are on broad-spectrum antibiotics, are they being de-escalated at 48 hours based on culture results, and are durations appropriate? The stewardship interventions that reduce CRE selection pressure are: restricting carbapenems and broad-spectrum cephalosporins to infectious diseases approval, mandatory 48-hour review of all antibiotics with de-escalation, IV-to-oral switch protocols, and facility-specific treatment guidelines that favour narrow-spectrum first-line therapy and short durations. I would also review whether there has been a recent increase in carbapenem or piperacillin-tazobactam use on the ward that might explain the emergence of CRE [6].

(e) Communication plan (2 marks): [1]

I would communicate the outbreak to: the ward staff (urgently, with clear instructions on isolation, hand hygiene, and equipment cleaning); the infection control team and clinical microbiologist (for surveillance, typing, and outbreak management); the hospital executive and the infectious diseases department (for resource allocation and institutional response); the patients (explanation of the screening process and the isolation precautions, with sensitivity to the stigma associated with MDRO colonisation); and the general practitioners and receiving facilities of colonised patients (for continuity of care and isolation on future admissions). The communication should be transparent, factual, and action-oriented, and it should include clear contact points for staff and patients with questions. I would document the outbreak investigation, the control measures implemented, and the outcome for the hospital's infection control records and quality improvement programme. [1]