Changing epidemiology of bacterial meningitis.

Immunization against the most common meningeal pathogens is the leading factor associated with decreased incidence of bacterial meningitis in countries where routine vaccination is available. This is most dramatically illustrated by the reduction in the incidence of Haemophilus influenzae type b meningitis. The incidence of bacterial meningitis has decreased by 55% since the introduction of the H. influenzae type b conjugate vaccine in 1990. H. influenzae occurred primarily in children younger than 5 years of age, and so the median age of patients with bacterial meningitis has now increased to 39 years of age in the United States, and the leading pathogen is currently Streptococcus pneumoniae. Three other control measures (ie, universal screening and antibiotic prophylaxis of pregnant women for Group B streptococci and the implementation and availability of the S. pneumoniae and Neisseria meningitidis conjugate vaccines) have likely further decreased the incidence of these meningeal pathogens. Lastly, the worldwide emergence of multidrug-resistant pneumococci has complicated the empiric therapy of bacterial meningitis.