COMMENTARY

Changing Incidence of Bacterial Meningitis

William T. Basco, Jr., MD

Disclosures

August 04, 2011

Bacterial Meningitis in the United States, 1998-2007

Thigpen MC, Whitney CG, Messonnier NE, et al; for the Emerging Infections Programs Network
N Engl J Med. 2011;364:2016-2025

Study Summary

Data for this study were obtained from a US Centers for Disease Control and Prevention-sponsored surveillance network. Data were collected between 1998 and 2007. For the purpose of this study, bacterial meningitis was defined as the presence of Streptococcus pneumoniae, Neisseria meningitidis, or Group B Streptococcus in a sample of cerebrospinal fluid. A patient was also considered to have meningitis if any of those bacteria were isolated from another sterile site when diagnosed with meningitis clinically by a healthcare provider. Cases of Listeria monocytogenes, obtained from a different surveillance network, were also included.

The surveillance networks identified 3188 cases of bacterial meningitis caused by the 4 pathogens. Over the time of the study, the incidence of bacterial meningitis declined by 31% (from 2.0 to 1.38 cases per 100,000 population). Age-related differences in the declining meningitis incidence were seen. No change in the incidence of bacterial meningitis was seen in children younger than 2 months of age. However, in all other pediatric age groups (2-23 months, 2-10 years, and 11-17 years of age) the incidence of bacterial meningitis dropped by 51%-64%.

The case-fatality rate for bacterial meningitis did not change significantly over the time period studied: from a rate of 17.9% in the first year of surveillance to 14.7% in the final year, a difference that did not reach statistical significance.

With the exception of Group B Streptococcus meningitis, the incidence of meningitis caused by all other pathogens declined over the study period. The incidence of bacterial meningitis due to S pneumoniae decreased by 26%, with the largest decline (92%) in S pneumoniae serotypes included in the 7-valent conjugate vaccine. Cases caused by nonvaccine pneumococci increased by 61% over the study period.

Qualitatively, Group B Streptococcus caused the overwhelming majority of bacterial meningitis cases in infants younger than 2 months of age. For all groups of older children, S pneumoniae comprised 45%-50% of cases of bacterial meningitis. This was followed by N meningitidis and a small but persistent proportion of cases caused by Haemophilus influenzae across the age ranges.

The investigators concluded that the incidence of bacterial meningitis caused by the pathogens studied declined in the past decade. The downward trend was primarily related to a decreasing incidence of bacterial meningitis caused by S pneumoniae. The largest reductions in cases of bacterial meningitis were in children, but case-fatality rates did not significantly improve.

Viewpoint

These data offer real encouragement to pediatric providers that we are gradually making progress in reducing the rate of this feared illness. However, many children still become ill with meningitis. It is very interesting that the relative contributions of the different pathogens did not change much over the study period. Group B Streptococcus remains the dominant organism in newborns with meningitis. S pneumoniae remains dominant in toddlers and young children, with almost equal contributions of S pneumoniae and N meningitidis in school-age children. Finally, the changing serotype mixture of S pneumoniae meningitis demonstrates the ability of the 7-valent pneumococcal conjugate vaccine to reduce pneumococcal meningitis. These data also indirectly support the expansion of the number of serotypes in the pneumococcal vaccine to the current 13-valent vaccine.

Abstract

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