A 28-year-old patient has been admitted to ICU intubated and ventilated with septic shock and multiorgan failure secondary to a methicillin sensitive Staphylococcus aureus bacteraemia. There is no known background medical history. Specific management has included intravenous flucloxacillin in appropriate dosages.
At day 7 they are stable requiring moderate vasopressor support, with ongoing dialysis. There is a persistent fever. Surveillance blood cultures continue to grow a methicillin sensitive Staphylococcus aureus.
Explain your assessment of this patient with regard to the positive blood cultures. (10 marks)
Syllabus topic/section:
2.1.3 Sepsis and Infections: Sepsis and septic shock: L1
Discussion:
Candidates that did well on this question recognised that it was an assessment of a patient with persistent MSSA bacteraemia without source control OR with an occult metastatic focus. Good answers provided a detailed examination to look for the potential sources and highlighted the significance of the investigation's requested by including the rationale for ordering them. For example, ECHO/TOE looking for endocarditis or MRI spine looking for epidural collection.
Some candidates interpreted the question as asking about a positive blood culture and therefore did not include a full assessment looking for other foci of infection. The question used the glossary of term “assessment”. Therefore, candidates needed to include information about the patient's history including risk factors for Staph bactereamias, a thorough examination specifically looking for source of recurrent staph, complications of septic shock and reversible elements of multiorgan failure with the relevant investigations to address this.
Candidates who scored poorly tended to have a very superficial approach to the examination and listed a large number of investigations without being more tailored to the specific question or including the rationale.
The marking rubric is included to aid the candidate’s future study.
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Below standard |
At Standard |
Above standard |
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Approach assessment in regard to positive blood cultures (10 marks) |
Insufficient assessment of specific patient described in stem. List only with no rationale for investigations provided. Basic / routine septic screen with not extended investigations. Omission of vital aspects of assessment (e.g. Staph risk factors, such as IVDU). Poorly structured. 0 – 4.5 marks |
Thorough approach with most assessments (general and specific to patient) outlined. Given the persistent Staph, and the direction to assess in regard to positive blood cultures: need to have extended search for metastatic/other foci of disease to achieve the standard required. Ie not just generic septic screen answer. some rationale provided. Not all assessments listed in ‘expected information’ are required for full marks, however some examples of further investigation based on history/exam findings would be expected. 5 -7 marks |
At standard plus Very clear approach containing the previous PLUS detailing the following
7.5 -10 marks |
The presence of the hidden ‘expected information’ in the rubric hints at the existence of a secret cheat sheet of information used by the examiners to mark these papers. Most likely these were lists of possible tests appended to the marking rubric to refresh the memories of the marking examiners, who were most likely not the same people who wrote the question, and who would not have had a recent opportunity to become content experts on this specific area of infectious disease. For these reasons, short refresher notes are occasionally made available, which make the grading easier, and which would not make any sense to release as "model answers" or anything such, mostly because they are not reflective of what is expected from the candidates nor representing a comprehensive list of expected knowledge (as they do not intend to cover every possible answer).
As in many of these questions, where a stem with history is offered, the answer should be tailored to the stem as much as possible, to avoid being criticised for being "generic". In this case the patient is:
So, they sound immunocompetent (as far as you know), and still shedding staph from somewhere. That sounds a lot like an uncontrolled occult source. The assessment is therefore focused on finding it.
History
Examination
Investigations
Foster, Timothy. "Staphylococcus." (1996).
Thwaites, Guy E., et al. "Clinical management of Staphylococcus aureus bacteraemia." The Lancet infectious diseases 11.3 (2011): 208-222.
Chong, Yong Pil, et al. "Persistent Staphylococcus aureus bacteremia: a prospective analysis of risk factors, outcomes, and microbiologic and genotypic characteristics of isolates." Medicine 92.2 (2013): 98.
Fowler, Vance G., et al. "Clinical identifiers of complicated Staphylococcus aureus bacteremia." Archives of internal medicine 163.17 (2003): 2066-2072.
Tong, Steven YC, et al. "Staphylococcus aureus infections: epidemiology, pathophysiology, clinical manifestations, and management." Clinical microbiology reviews 28.3 (2015): 603-661.