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Breakthrough OPSI — SCE Infectious Diseases MCQ

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ModerateInfection Prevention & ControlBreakthrough OPSISCE Infectious Diseases

A 60-year-old man with a prosthetic aortic valve has been taking prophylactic Phenoxymethylpenicillin after splenectomy. He develops Streptococcus pneumoniae bacteraemia despite prophylaxis. What is the most likely explanation?

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Correct answer: A — Penicillin-resistant S. pneumoniae — breakthrough pneumococcal infection can occur with resistant strains despite prophylaxis

Penicillin-resistant S. pneumoniae is an important cause of breakthrough infections in asplenic patients on penicillin prophylaxis. While penicillin prophylaxis significantly reduces OPSI risk, it does not eliminate it — particularly with rising penicillin resistance rates. This is why vaccination (PCV13 plus PPV23) is equally important. If breakthrough occurs, empirical treatment should include agents active against resistant pneumococci (IV Ceftriaxone ± Vancomycin for meningitis). Adherence to prophylaxis should also be verified, and patients should carry emergency standby antibiotics.

Reference: UKHSA 2024 – Green Book Ch 7: Asplenia; NICE 2024 – Asplenia