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Meningitis cases low, yet mortality high in older adults
Thigpen MC. NEJM. 2011;364: 2016-2025.
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Despite the significant decrease in bacterial meningitis among US children since the 1998 introduction of the pneumococcal and Haemophilus influenzae type b conjugate vaccines, older adults now bear the burden of the disease.
As the epidemiology of meningitis has changed since the early 90’s, Michael C. Thigpen, MD, and colleagues at the CDC pooled data on bacterial meningitis cases (n=3,155) to identify trends in meningitis in the US between 1998 and 2007.
Meningitis cases decreased from 2.0 cases per 100,000 population between 1998 and 1999 (95% CI, 1.85-2.15) to 1.38 cases per 100,000 population between 2006 and 2007 (95% CI, 1.27-1.50). Between 2003 and 2007, approximately 4,100 cases and 500 deaths occurred annually from meningitis.
Researchers observed no significant change in the overall case fatality rate among adults during 1998-1999 and 2006-2007 (15.7% during 1998-1999 and 14.3% during 2006-2007; P=.50). Moreover, the case fatality rate increased linearly with increasing age (8.9% among patients age 18 to 84 vs. 22% among those 65 years and older) (P<.001).
Compared with 587 cases of meningitis in children between 2003 and 2007, there were 1,087 cases among adults. Cases among adults were predominantly identified as Streptococcus pneumoniae (58%). This was followed by group B streptococcus (18.1%), Neisseria meningitidis (13.9%), Haemophilus influenzae (6.7%), and Listeria monocytogenes (3.4%).
“Although the epidemiology of bacterial meningitis has evolved from 1998 to 2007, the rank order of causative pathogens has changed relatively little,” according to the researchers.
“Our findings indicate that the incidence of bacterial meningitis caused by H. influenzae, S. pneumoniae, L. monocytogenes, or N. meningitidis decreased in the past decade, primarily due to declines in the rate of S. pneumoniae meningitis,” the researchers reported. “Rates of bacterial meningitis decreased most sharply among children, causing the median age at diagnosis of bacterial meningitis to increase. However, this achievement only reemphasizes the need for interventions targeting neonates and elderly persons — the two populations in which the meningitis burden remains greatest.”
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