Asplenic patients are at increased risk for meningitis due to which organism?

• A. Streptococcus pneumoniae
• B. Neisseria meningitidis
• C. Haemophilus influenzae
• D. Listeria monocytogenes

Answer: (A)

The spleen helps clear encapsulated bacteria from the bloodstream, using opsonizing antibodies against polysaccharide capsules. When the spleen is absent or nonfunctional, people become especially susceptible to invasive infections by encapsulated organisms. Among organisms that commonly cause meningitis and are encapsulated, Streptococcus pneumoniae is the classic one tied to asplenia. This organism is a leading cause of adult meningitis, and without splenic clearance and opsonization, the risk of pneumococcal meningitis rises notably in asplenic individuals.

Neisseria meningitidis can also cause meningitis and is encapsulated, but the strongest and most well-established link with asplenia is with pneumococcus. Haemophilus influenzae type b is another encapsulated pathogen that can cause meningitis, though vaccination and changing epidemiology have reduced its incidence. Listeria monocytogenes is not encapsulated and tends to affect the very young, the elderly, pregnant individuals, and those with certain immunocompromising conditions, rather than being specifically associated with absence of the spleen.