What is the common causative agent of meningitis in adults?

Streptococcus pneumoniae is the most common causative agent of meningitis in adults. This encapsulated gram-positive bacterium is a leading cause of bacterial meningitis in individuals over the age of 18. It can be particularly prevalent in populations with higher rates of pneumonia, as it is also a major pathogen responsible for pneumonia and otitis media.

S. pneumoniae can invade the central nervous system following respiratory tract infections or sinusitis, leading to the development of meningitis. In addition to its virulence factors, the polysaccharide capsule of S. pneumoniae plays a crucial role in its ability to evade the host’s immune response.

In contrast, while other organisms such as Escherichia coli, Neisseria gonorrhoeae, and Haemophilus influenzae are associated with meningitis, they are less common in adult populations. E. coli is more frequently related to meningitis in neonates, N. gonorrhoeae primarily causes gonococcal infections, and H. influenzae, though historically significant, has seen a decrease in cases due to vaccinations targeting its type b strain. Thus, S. pneumoniae stands out as the predominant causative agent in adults.