In adults, the most common meningitis pathogens are which two organisms?

• A. Listeria monocytogenes and Escherichia coli
• B. Group B Streptococcus and Haemophilus influenzae
• C. Streptococcus pneumoniae and Neisseria meningitidis
• D. Neisseria meningitidis and Haemophilus influenzae

Answer: (C)

In adults with bacterial meningitis, the two most common pathogens are Streptococcus pneumoniae and Neisseria meningitidis. Streptococcus pneumoniae is the leading cause overall in adults, often arising from or following pneumonia or sinusitis, and it has a polysaccharide capsule that helps it invade the bloodstream and reach the meninges. Neisseria meningitidis is particularly common in adolescents and young adults who live in close-contact settings, like dormitories or military housing, and it can spread in the nasopharynx and cross into the meninges, sometimes presenting with meningococcemia. Vaccination has reduced Haemophilus influenzae type b as a cause, and Escherichia coli is more typical of neonatal meningitis, while Listeria monocytogenes is more likely in the elderly or immunocompromised. So, the two most common adult meningitis pathogens are Streptococcus pneumoniae and Neisseria meningitidis.