By Serena Gordon
WEDNESDAY, May 25 (HealthDay News) -- The incidence of bacterial meningitis dropped by 31 percent between 1998 and 2007, new government research shows.
The drop was led by reductions in infections by two powerful germs -- Neisseria meningitidis and Streptococcus pneumoniae -- that are covered by available immunizations. With fewer infections among young children, the burden of the disease is now mainly borne by older adults, the study authors found.
"The good news is that fewer people are getting bacterial meningitis. The bad news is that if you get it, it's still a very serious infection," said study co-author Dr. Cynthia Whitney, chief of the bacterial respiratory diseases branch at the U.S. Centers for Disease Control and Prevention in Atlanta.
"There are still at least 4,000 cases a year, including about 500 that are fatal," she noted.
Results of the study are published in the May 26 issue of the New England Journal of Medicine.
Bacterial meningitis is a dangerous bacterial infection that causes inflammation of the membranes that cover the brain and spinal cord, according to the CDC.
Signs of meningitis in people over the age of 2 include fever, headache and stiff neck, according to the CDC, while symptoms in newborns and infants can include fever, seizures, constant crying, a bulge in the soft spot on the head and stiffness in the body and neck. Bacterial meningitis can be contagious.
The five types of bacteria that were most responsible for bacterial meningitis in the 1970s and 1980s were Haemophilus influenzae, N. meningitidis, S. pneumoniae, group B streptococcus and Listeria monocytogenes, according to the study.
In the late 80s and early 90s, the incidence of bacterial meningitis dropped by 55 percent, likely because an infant vaccine was introduced in 1990 for H. influenzae type B (Hib).
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 common strains. The Hib vaccine, which covers H. influenzae, is part of routine childhood immunizations.
The meningoccocal vaccine (MCV4), which protects against N. meningitidis, covers against a form of bacterial meningitis that is often passed from person-to-person when many people are living in close quarters, such as a college dormitory or military barracks. The CDC recommends the first dose of this vaccine be given at 11 to 12 years old, and then a booster at 16 years old; it's also recommended for certain high-risk children aged 2 through 10. If you're over 16 when you first receive this vaccine, the CDC says only one dose is needed.