Effect of pneumococcal conjugate vaccine on pneumococcal meningitis

Abstract

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.

Figure 1. Mean Annual Incidence of Pneumococcal Meningitis, According to Serotype Group and Time Period

Serotypes of the heptavalent pneumococcal conjugate vaccine (PCV7) were 4, 6B, 9V, 14, 18C, 19F, and 23F. PCV7-related serotypes were 6A, 9A, 9L, 9N, 18A, 18B, 18F, 19B, 19C, 23A, and 23B. Non-PCV7 serotypes were 3, 7F, 10A, 11A, 12F, 15A, 15B/C, 16F, 19A, 22F, 33F, 35B, 35F, and 38.

Figure 2. Percentage of Pneumococcal Isolates, from 1239 Cases, That Were Nonsusceptible to Various Antibiotics, According to Year and Degree of Nonsusceptibility

For 1998–2005, 140 isolates lacking serotype or susceptibility data were excluded. The total number of isolates tested was 147 in 1998, 191 in 1999, 179 in 2000, 154 in 2001, 161 in 2002, 155 in 2003, 119 in 2004, and 133 in 2005. In 2002, only 160 of the 161 isolates were tested for susceptibility to chloramphenicol.