Rates of bacterial meningitis dropped markedly among all age groups in the United States during the past decade but have declined most strikingly in children, according to a report in the May 26 issue of the New England Journal of Medicine.
This trend is probably the result of the success of pneumococcal and Hib conjugate vaccines in preventing these infections in early childhood. The epidemiology of bacterial meningitis has shifted, with the most obvious change being the increase in the average patient age at diagnosis, according to Dr. Michael C. Thigpen of the Centers for Disease Control and Prevention, Atlanta, and his associates.
The investigators tracked changes in the epidemiology of bacterial meningitis cases from 1998 through 2007 using data from two surveillance systems, one laboratory based and the other population based, in the CDC’s Emerging Infections Program network. The network covered approximately 17.4 million people residing in eight regions of the country during the study period.
The researchers identified 3,188 cases of bacterial meningitis resulting from the five most common causative organisims: Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, group B streptococcus, or Listeria monocytogenes. The overall fatality rate was 15%.
The overall incidence of these infections declined from 2.00 cases per 100,000 people to 1.38 per 100,000 – approximately 30%.
Rates of meningitis declined most dramatically among children, probably because of the introduction of the PCV7 vaccine. This decline correlated with a rise in the median age of bacterial meningitis patients, from about 30 years to 42 years.
The incidence of bacterial meningitis also declined among adults aged 65 and older and may decline further in this age group because of reduced exposure as more "children are vaccinated with the newly licensed PCV13," Dr. Thigpen and his colleagues said (N. Engl. J. Med. 2011;364:2016-25).
Nevertheless, the case fatality rate did not change significantly. It was 15.7% in 1998 and 14.3% in 2007.
Although the epidemiology of bacterial meningitis has changed, the ranking of causative organisms has not. "For clinicians, [this suggests] that current treatment guidelines ... targeting the major pathogenic causes are still appropriate."
S. pneumoniae was the most common causative pathogen among adults as well as children aged 1-11 years. Group B strep accounted for most cases among infants, and that rate did not decrease.
The rate of N. meningitidis infection decreased, but that organism still accounted for most cases of bacterial meningitis that developed in adolescents. "As the proportion of children receiving MCV4 continues to increase, we expect additional reductions in the incidence of meningococcal disease," the investigators said.
This study probably underestimates the true burden of bacterial meningitis for three main reasons.
First, the databases only included culture-proven cases, and the accuracy of that identification "depends on the diagnostic and therapeutic practices of those caring for patients," they said.
Second, the databases did not cover all the possible pathogens that cause bacterial meningitis, such as Escherichia coli and some species of staph.
Third, the databases do not routinely collect information on cases acquired in health care settings, "which may account for up to 40% of cases," Dr. Thigpen and his associates said.
The study was supported by the Centers for Disease Control and Prevention. Some of Dr. Thigpen’s associates reported financial ties to Merck, Wyeth, Sanofi Pasteur, Novartis, GlaxoSmithKline, and Pfizer.