Epidemiological analysis on two decades of hospitalisations for meningitis in the United States.

Bacterial meningitis is an important source of mortality and morbidity worldwide. Data exist on specific vaccines against Streptococcus pneumoniae and Neisseria meningitidis indicating that they reduce the incidence of meningitis, yet comprehensive information on the trend of bacterial meningitis is still lacking. We analysed the Kids' Inpatient Database and the National Inpatient Database considering all bacterial meningitides in the United States, excluding cases of tuberculosis and sexually transmitted diseases. We analysed the trend of meningitis incidence from 1993 to 2011 and in specific age groups before and after the introduction of the pneumococcal conjugate vaccine 7 (PCV-7) and the meningococcal conjugate vaccine 4 (MCV-4). Moreover, we analysed the prevalence of aetiological agents to assess their changes. We estimated 295,706 cases of meningitis having occurred in the United States and a reduction of the discharge rate of 21 %. We observed a significant reduction in cases of meningitis in children and elderly patients following the introduction of the PCV-7. We also found a reduction in subjects aged 10-14 years, an age span consistent with the introduction of MCV-4, although further analyses based on serotypes data are required to confirm this observation. By contrast, we observed an increased prevalence of cases of staphylococcal and streptococcal meningitides. The introduction of PCV-7 has reduced the incidence and changed significantly the aetiology of bacterial meningitis in the United States during the last two decades.