Clonal Distribution of Invasive Pneumococcal Isolatesfrom Children and Selected Adults in the United States Prior to7-Valent Conjugate VaccineIntroduction

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Abstract
Theseven-valent pneumococcal conjugated polysaccharide vaccine PC7V was licensed for use among children in 2000. Since 90 serotypes of pneumococci exist, an increase in nonvaccine serotypes could occur through immune selection for capsular type switching. Eleven hundred sixty-eight invasive isolates (24 serotypes), recovered primarily from pediatric patients (855 isolates = 73%) and 22 reference strains of known multilocus sequence types (STs) were subjected to macrorestriction profiling (pulsed-field gel electrophoresis [PFGE]). The correlation of 187 ST results (including 49 newly discovered STs) with the PFGE data assigned 1,042 (89.2%) study isolates to 46 defined clonal complexes or genetic lineages based on related multilocus STs (BURST). Seventeen clonal complexes were represented by 2 to 10 related allelic profiles (STs), while 33 lineages (including reference strains) consisted of single STs with 4 or fewer allelic identities to other STs found in the study. Expansion of the BURST analysis to a global analysis of all known pneumococcal STs (as of 27 November 2002) reduced the number of single ST lineages from 33 to 8, and the number of multi-ST clonal complexes was reduced from 17 to 13. In this work, we established the basic genetic structure within individual serotypes prior to PC7V use. The resultant database will be useful for detecting potential selective effects of this vaccine in postvaccine surveillance.

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