Infections in the Immunocompromised Host — Viva

Long Case Viva Defence

Candidate's opening statement (model answer)

"Mr David Tran is a 62-year-old retired engineer with newly diagnosed acute myeloid leukaemia, admitted on day 12 of 7+3 induction (cytarabine and daunorubicin). He presented on the ward with a fever to 38.8 degrees Celsius and a neutrophil count of 0.1 x 10^9 per litre, in the setting of severe oral mucositis and a tunnelled central venous catheter. He was managed as febrile neutropenia, with blood cultures drawn from a peripheral vein and from each lumen of the central catheter followed by immediate empiric piperacillin-tazobactam 4.5 g intravenously, and vancomycin was added for severe mucositis on ciprofloxacin prophylaxis and possible line-site infection. ^[1]

His main problems are:

1. Febrile neutropenia complicating AML induction, currently day 5 of persistent fever despite broad-spectrum antibacterials.
2. Invasive pulmonary aspergillosis, confirmed today on chest CT (a halo sign in the right upper lobe), a serum galactomannan of 2.1, and a bronchoalveolar lavage positive for Aspergillus galactomannan and culture.
3. Severe chemotherapy-induced mucositis.
4. Central venous catheter in situ, with ongoing assessment for line-related infection.
5. The underlying acute myeloid leukaemia, for which the timing of re-induction or consolidation must be reconsidered in light of the fungal infection. ^[1]

His management to date has been the febrile neutropenia protocol on day 0, the addition of empiric liposomal amphotericin B on day 4 for persistent fever, and confirmation of invasive aspergillosis on day 5 with a plan to switch to voriconazole as first-line therapy, reduce immunosuppression where possible, and continue antifungal treatment for a minimum of 6 to 12 weeks with galactomannan and imaging monitoring." ^[1]

Examiner probing questions and model answers

Q1: "Walk me through why the empiric regimen for febrile neutropenia is an antipseudomonal beta-lactam as monotherapy, and why you do not add an aminoglycoside or vancomycin routinely." ^[1]

"The empiric regimen must cover the highest-risk organism from the first dose, and in neutropenia that organism is Pseudomonas aeruginosa — its bacteraemia in the neutropenic patient can kill within hours. The IDSA 2011 guideline recommends an antipseudomonal beta-lactam — piperacillin-tazobactam, cefepime, or a carbapenem — as empiric monotherapy ^[1]. The move away from beta-lactam plus aminoglycoside combination is driven by a Cochrane review of 71 trials, which found that beta-lactam monotherapy is as effective as combination therapy for mortality and treatment failure, with significantly less nephrotoxicity ^[2]. The aminoglycoside era for routine empiric febrile neutropenia is over. Vancomycin is added only for specific indications — suspected catheter-related infection, severe sepsis or shock, pneumonia, skin or soft-tissue infection, MRSA colonisation, severe mucositis on fluoroquinolone prophylaxis, or a positive Gram-positive blood culture — because routine vancomycin increases nephrotoxicity without improving outcomes. In Mr Tran I added it for two of those indications: the severe mucositis on ciprofloxacin prophylaxis, where viridans streptococci are the concern, and the possible line-site infection."

Q2: "He is now day 5 and persistently febrile. How did you make the diagnosis of invasive aspergillosis, and what is your treatment?" ^[1]

"Persistent fever beyond 3 to 5 days despite broad-spectrum antibacterials mandates evaluation for invasive fungal infection. I ordered a high-resolution chest CT rather than a chest X-ray, because the chest X-ray is often normal early — the CT is the test that finds the halo sign, which is a nodular lesion surrounded by a ground-glass halo of haemorrhage, the early radiological signature of angioinvasive aspergillosis. The right upper lobe halo sign, combined with a serum galactomannan of 2.1 (positive, above 0.5), a bronchoalveolar lavage galactomannan positive, and a culture growing Aspergillus fumigatus, meets the EORTC/MSG criteria for proven invasive aspergillosis. My treatment is voriconazole first-line — established by the seminal randomised trial showing a survival benefit over amphotericin B deoxycholate — loaded at 6 mg/kg every 12 hours for two doses then 4 mg/kg every 12 hours, transitioning to oral 200 mg every 12 hours once he can absorb. I will monitor the voriconazole level (target trough 1 to 5.5 mg/L) because of its variable pharmacokinetics, watch for hepatotoxicity and the visual disturbances, and monitor the galactomannan and CT for response. Isavuconazole is an equivalent alternative. I will reduce his immunosuppression where the haematology team permits, and continue treatment for a minimum of 6 to 12 weeks, with the duration guided by clinical and radiological response, galactomannan clearance, and immune reconstitution. The mortality of invasive aspergillosis in the neutropenic and transplant population is 50 to 60 per cent despite treatment, so this is a serious turn in his admission." ^[1]

Q3: "Would you give him G-CSF now?" ^[1]

"No, not routinely. A Cochrane review of 14 randomised controlled trials by Mhaskar and colleagues (2014) found that adding colony-stimulating factors to antibiotics for established febrile neutropenia did not significantly reduce overall mortality (hazard ratio 0.74, 95 per cent confidence interval 0.47 to 1.16) ^[3]. Although G-CSF does modestly shorten the duration of neutropenia, this does not translate into a survival benefit. I would reserve it for selected patients with features predicting a poor outcome — profound and prolonged neutropenia expected to last beyond 10 days, pneumonia, invasive fungal infection, or haemodynamic instability — as a considered decision. Mr Tran does now have an invasive fungal infection, so I would discuss G-CSF with the haematology team as an adjunct, but I would not present it as routine or as a substitute for the antifungal therapy. His legitimate G-CSF role is primary prophylaxis for the next cycle if the regimen's expected febrile neutropenia risk is above 20 per cent, and secondary prophylaxis after this confirmed episode to allow maintenance of dose intensity."

Q4: "How does the diagnosis and the timing of invasive fungal infection change the plan for his leukaemia treatment?" ^[1]

"This is the central conversation with the haematology team. Invasive aspergillosis is a relative contraindication to further intensive chemotherapy in the immediate term, because the next cycle will prolong the neutropenia and worsen the fungal infection. The principles are: complete the antifungal induction and achieve a clinical and microbiological response first; consider whether a less myelosuppressive regimen, a delayed consolidation, or a bridging strategy is appropriate; and continue secondary antifungal prophylaxis throughout subsequent chemotherapy cycles and through any haematopoietic stem cell transplant. If he is a candidate for allogeneic transplant, the aspergillosis must be controlled beforehand, and antifungal prophylaxis (posaconazole or voriconazole, given their mould cover) continues through the transplant — the CDC/IDSA/ASBMT guidelines underpin this ^[4]. The decision is a multidisciplinary one between haematology, infectious diseases, and clinical microbiology, and it is guided by the response of the fungal infection (galactomannan trend, CT resolution, immune recovery) and the leukaemia kinetics."

Q5: "He recovers from the aspergillosis. What prophylaxis will he need for the rest of his treatment course?" ^[1]

"During subsequent neutropenic phases he should receive mould-active antifungal prophylaxis — posaconazole or voriconazole — because he has now had invasive aspergillosis and is at very high risk of recurrence with the next cycle. He should continue co-trimoxazole for PCP prophylaxis during and after any corticosteroid-containing regimen and through any transplant. He should continue aciclovir for HSV/VZV. He should be screened for CMV, HBV (HBsAg and anti-HBc), HCV, and HIV before any future chemo or biologic, and receive HBV prophylaxis if positive. He should receive his age-appropriate vaccinations (influenza annually, pneumococcal, COVID-19, recombinant zoster) during remission and off intensive therapy, with the inactivated vaccines given at least 2 weeks before the next cycle and live vaccines deferred entirely until immune reconstitution is documented. The principle is that the infection history drives the prophylaxis plan, and that the plan must be explicit, written, and communicated to the patient and the general practitioner." ^[1]

Q6: "How will you counsel him and his family about what has happened, and the road ahead?" ^[1]

"I will be honest and clear. I will explain that the chemotherapy lowered his white cells to a point where he could not fight infection, that a fever was the warning sign, and that we treated it immediately with antibiotics through the drip. I will explain that the persistent fever led us to look for a fungal infection, which we found in the lung, and that we are now treating it with a targeted antifungal that we will continue for several months. I will be honest that this is a serious complication and that it changes the timing of his leukaemia treatment, but that we have a clear plan with the haematology team. I will ask about his values and goals — what matters most to him, what his understanding of prognosis is, and whether he wishes to continue intensive treatment — and I will involve the palliative care team early for symptom support alongside disease-directed therapy if he wishes. I will give written information and a clear point of contact for questions, and I will arrange a family meeting with haematology, infectious diseases, and nursing. The communication is as important as the antibiotics." ^[1]