Effect of Pneumococcal Conjugate Vaccine on Pneumococcal Meningitis

Background Invasive pneumococcal disease declined among children and adults after the introduction of the pediatric heptavalent pneumococcal conjugate vaccine ( PCV7) in 2000, but its effect on pneumococcal meningitis is unclear. Methods We examined trends in pneumococcal meningitis from 1998 through 2005 using active, population- based surveillance data from eight sites in the United States. Isolates were grouped into PCV7 serotypes ( 4, 6B, 9V, 14, 18C, 19F, and 23F), PCV7- related serotypes ( 6A, 9A, 9L, 9N, 18A, 18B, 18F, 19B, 19C, 23A, and 23B), and non- PCV7 serotypes ( all others). Changes in the incidence of pneumococcal meningitis were assessed against baseline values from 1998- 1999. Results We identified 1379 cases of pneumococcal meningitis. The incidence declined from 1.13 cases to 0.79 case per 100,000 persons between 1998- 1999 and 2004- 2005 ( a 30.1% decline, P< 0.001). Among persons younger than 2 years of age and those 65 years of age or older, the incidence decreased during the study period by 64.0% and 54.0%, respectively ( P< 0.001 for both groups). Rates of PCV7- serotype meningitis declined from 0.66 case to 0.18 case ( a 73.3% decline, P< 0.001) among patients of all ages. Although rates of PCV7- related- serotype disease decreased by 32.1% ( P = 0.08), rates of non- PCV7- serotype disease increased from 0.32 to 0.51 ( an increase of 60.5%, P< 0.001). The percentages of cases from non- PCV7 serotypes 19A, 22F, and 35B each increased significantly during the study period. On average, 27.8% of isolates were nonsusceptible to penicillin, but fewer isolates were nonsusceptible to chloramphenicol ( 5.7%), meropenem ( 16.6%), and cefotaxime ( 11.8%). The proportion of penicillin-nonsusceptible isolates decreased between 1998 and 2003 ( from 32.0% to 19.4%, P = 0.01) but increased between 2003 and 2005 ( from 19.4% to 30.1%, P = 0.03). Conclusions Rates of pneumococcal meningitis have decreased among children and adults since PCV7 was introduced. Although the overall effect of the vaccine remains substantial, a recent increase in meningitis caused by non- PCV7 serotypes, including strains nonsusceptible to antibiotics, is a concern.