Since that time, other vaccines have been introduced for strains of N. meningitidis and S. pneumoniae that appear responsible for the shrinking infection rate caused by those germs. The rate of one type of S. pneumoniae decreased by 92 percent during the study period, and the incidence of N. meningitidis dropped by 58 percent.
The findings were based on information from the CDC's Emerging Infections Programs Network, which included eight surveillance sites across the United States. These sites include data on about 17.4 million people.
During the surveillance period between 1998 and 2007, the incidence of bacterial meningitis dropped from two cases per 100,000 people to 1.38 cases per 100,000 people. The average age of those affected increased from 30.3 years to 41.9 years.
The incidence of meningitis was highest among blacks and children under 2 months old throughout the study period, the CDC reported.
In addition, rates of death caused by bacterial meningitis didn't change significantly over the study period. Among adults, those aged 65 or older were most likely to die from the illness.
The youngest and oldest people are typically more susceptible to infections from a variety of causes, but Whitney said that the CDC researchers aren't sure why blacks have significantly higher rates of bacterial meningitis.
Kenneth Bromberg, director of the Vaccine Study Center at the Brooklyn Hospital Center, said it can be difficult to tease out the reasons why certain groups have higher rates of some infections: Is it an inherent susceptibility? Is it an access-to-care issue? In this case, he said he thinks that black people may have a genetic susceptibility to certain bacteria that cause meningitis.
There are three different types of vaccines available for bacterial meningitis. These vaccines don't cover every strain that can cause meningitis, but they do offer protection against many of the com
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