SAN FRANCISCO — Populationwide rates of bacterial meningitis declined significantly from 1.9 cases per 100,000 people in 1998 to 1.5 per 100,000 in 2003, largely due to a pediatric vaccine that seems to have no herd effect in older people, Michael C. Thigpen, M.D., said.
Dr. Thigpen of the Centers for Disease Control and Prevention, Atlanta, and his associates analyzed surveillance data from nine geographic areas covering a population of 17 million in 1998 and 25 million in 2002. The 2,039 cases of bacterial meningitis in the study killed 16% of patients.
The pneumococcal 7-valent conjugate vaccine (PCV-7) was recommended in 2000 for infants aged 2–23 months; the incidence of pneumococcal meningitis subsequently declined 65% in that age group. No decline in pneumococcal meningitis occurred in older people, as has been seen with other types of invasive pneumococcal disease after the introduction of PCV-7, he said at the annual meeting of the Infectious Diseases Society of America.
Cyclical changes in meningococcal disease also contributed to the reduced incidence of bacterial meningitis. Five pathogens cause 80% of bacterial meningitis: Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae type b, group B streptococcus (GBS), and Listeria monocytogenes.
Recommendations in 2002 for universal GBS screening of pregnant women and the 2005 licensing of meningococcal conjugate vaccine (MCV-4) for youths aged 11–17 years may further affect the incidence of bacterial meningitis. “It remains to be seen how universal GBS screening and MCV-4 will change the epidemiology of bacterial meningitis,” he said.
Among 781 cases of bacterial meningitis reported in 2002–2003, the most common pathogen was S. pneumoniae, accounting for 61% of cases and 76% of deaths. N. meningitidis caused 16% of cases, GBS caused 14%, H. influenzae caused 7%, and Listeria caused 2%.
Because of the success in reducing pneumococcal meningitis in the youngest age group, the median age of patients rose to 39 years. The disease killed 5% of patients younger than 2 months and 28% of patients aged 65 years or older.
“As bacterial meningitis has become even more a disease of adults, with S. pneumoniae causing disease across all ages, further reductions using a targeted approach may be difficult. … Broad strategies, including new vaccines to prevent adult cases of bacterial meningitis, should be considered,” he said.