Which organisms are the common causes of meningitis in adults aged 18-65 years?

• A. Streptococcus pneumoniae and Neisseria meningitidis
• B. Listeria monocytogenes and Escherichia coli
• C. Haemophilus influenzae and Neisseria gonorrhoeae
• D. Pseudomonas aeruginosa and Bacillus cereus

Answer: (A)

In adults aged 18–65 who develop meningitis, the most common culprits are Streptococcus pneumoniae and Neisseria meningitidis. Streptococcus pneumoniae is the leading cause across age groups and often sits in the nasopharynx as a colonizer that can invade the meninges, especially in people with risk factors like asplenia, alcoholism, or other immune risks. Neisseria meningitidis is another frequent cause, particularly in younger adults and in crowded settings, where transmission is more common.

Other organisms listed are less typical for this age range. Listeria monocytogenes is more a concern in older adults and immunocompromised individuals. Escherichia coli is primarily a neonatal pathogen. Haemophilus influenzae incidence has dropped in adults due to vaccination. Neisseria gonorrhoeae can cause meningitis but is rare. Pseudomonas aeruginosa and Bacillus cereus are usually associated with hospital- or device-related infections or specific risk factors rather than community-acquired meningitis in this age group.

So the combination of Streptococcus pneumoniae and Neisseria meningitidis best represents the common causes of meningitis in adults 18–65.