Infective endocarditis — formative SAQs

Question 1 (12 marks)

A nine-year-old girl with a history of repaired tetralogy of Fallot presents with two weeks of low-grade fever, fatigue and anorexia. On examination she has a new harsh diastolic murmur. Three sets of blood cultures drawn before antibiotics grow viridans streptococci. Echocardiography shows a vegetation on the aortic valve. [1]

a) List the two MAJOR criteria of the Modified Duke criteria and state how this case meets the definition of definite endocarditis. (4 marks) [3]

b) Outline the principles of targeted antibiotic therapy for this child, including the duration. (4 marks) [1]

c) Describe two clinical findings that would prompt urgent surgical referral during her admission. (4 marks) [1]

Question 2 (8 marks)

A neonate in the neonatal intensive care unit has a long-standing central venous catheter. Blood cultures grow Staphylococcus aureus that persists despite seventy-two hours of appropriate flucloxacillin. The cardiac murmur is unremarkable. [5]

a) What is the most likely diagnosis, and why is the murmur unremarkable? (3 marks) [1]

b) State the two key management actions beyond continuing antibiotics. (3 marks) [1]

c) Give one reason why Staphylococcus aureus has overtaken viridans streptococci as a leading cause of paediatric endocarditis in this setting. (2 marks) [5]

Model answer notes (for examiner use, not for candidates)

Q1a) The two major Modified Duke criteria are (1) a typical micro-organism in two separate blood cultures and (2) echocardiographic evidence of endocardial involvement (a vegetation, an abscess, or a new partial dehiscence of a prosthetic valve). This case is definite endocarditis: two major criteria (typical organism in separate cultures plus an echocardiographic vegetation). [3]

Q1b) Targeted therapy is narrowed to the organism and its sensitivities \u2014 viridans streptococci, penicillin-susceptible, answered by penicillin or ceftriaxone, with or without a short course of gentamicin for synergy. Therapy runs for four to six weeks intravenously because the biofilm within the vegetation shields the organism from a short course. [1]

Q1c) Heart failure from acute valve regurgitation (the commonest surgical indication) and a perivalvular abscess, signalled by a new atrioventricular block, both demand urgent surgical referral. [1]

Q2a) Right-sided infective endocarditis on a tricuspid or pulmonary valve from the central line. The murmur is often absent in right-sided disease, so the clue is the persistent staphylococcal bacteraemia and the line rather than the murmur. [1]

Q2b) Perform echocardiography to look for a vegetation, and remove the infected central line. Leaving the line in place converts a treatable bacteraemia into a destructive endocarditis. [1]

Q2c) The widespread use of indwelling central venous catheters in neonates and children with complex medical needs has made Staphylococcus aureus the leading organism, particularly in right-sided, line-associated disease. [5]