Changing Epidemiology of Bacterial Meningitis in the United States.

Bacterial meningitis is an important cause of morbidity and mortality in the United States and throughout the world. Over the past 20 years, there have been significant changes in the epidemiology of bacterial meningitis. The most important change is the decrease in the frequency of Haemophilus influenzae type b as the most common etiologic agent of bacterial meningitis, since the H. influenzae type b conjugate vaccine was introduced. Streptococcccus pneumoniae is now the major cause of bacterial meningitis in the US and bacterial meningitis is now a disease predominantly of adults, rather than of infants and children. Emergence of antimicrobial resistance in S. pneumoniae has also altered the approach to antimicrobial therapy in patients with pneumococcal meningitis, indicating the need to use preventive strategies to reduce the frequency of this serious infection. Recent licensure of the heptavalent pneumococcal conjugate vaccine will likely decrease the overall incidence of pneumococcal meningitis.