Final answer:
The most common causative organisms of meningitis in adults include Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae, with Streptococcus pneumoniae being the leading cause post-Hib vaccine era.
Step-by-step explanation:
The most common causative organisms of meningitis in adults are Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae. Specifically, Streptococcus pneumoniae has become the leading cause of meningitis from the age of 2 months through adulthood following the introduction of the Hib vaccine. These bacteria can traverse the mucous membranes and enter the bloodstream, leading to infections, such as meningitis. Without treatment, bacterial meningitis can be fatal, and survivors may suffer from permanent disabilities.
While the prevalence of Neisseria meningitidis, also known as meningococcal meningitis, is higher among certain age groups, such as infants, adolescents, and young adults, the incidence of meningococcal meningitis epidemics has decreased significantly in many areas due to the use of vaccines. Meanwhile, Haemophilus influenzae mainly affects young children and neonates. Prompt treatment with appropriate antibacterial therapy significantly lowers the mortality rates of bacterial meningitis.