Question

A post-splenectomy patient is at greatest risk of overwhelming sepsis from which organism?

• A. Streptococcus pneumoniae
• B. Staphylococcus aureus
• C. Escherichia coli
• D. Pseudomonas aeruginosa

Hint:

No spleen = no clearance of encapsulated bugs; the top one is pneumococcus.

Answer 1

The Correct Option is A

Step 1: Understand the immune role of the spleen. The spleen is the principal site for clearing encapsulated bacteria from the blood and for mounting opsonising IgM/complement responses. Loss of the spleen (asplenia) markedly impairs clearance of capsular organisms.

Step 2: Recall the encapsulated organisms. The classic asplenia/OPSI triad is Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitidis. Among these, Streptococcus pneumoniae is by far the most common cause of overwhelming post-splenectomy infection (OPSI), responsible for roughly 50-90% of cases.

Step 3: Clinical relevance. Because of this risk, asplenic patients receive pneumococcal, Hib, and meningococcal vaccination (ideally before elective splenectomy) plus often prophylactic penicillin.

Step 4: Why the others are wrong. S. aureus, E. coli and Pseudomonas are not predominantly capsule-dependent for splenic clearance and are not the signature OPSI pathogens; they cause sepsis through different, non-asplenia-specific mechanisms.

Key fact: The commonest cause of overwhelming post-splenectomy sepsis is Streptococcus pneumoniae.