Population snapshot of Streptococcus pneumoniae serotype 19A isolates before and after introduction of seven-valent pneumococcal Vaccination for French children

Abstract

Serotype 19A Streptococcus pneumoniae strains are now more frequent in French children than before the introduction of a seven-valent conjugate vaccine (PCV7). By applying multilocus sequence typing to 144 serotype 19A isolates collected before and after beginning PCV7 vaccination, we detected clonal expansion of the preexisting penicillin-intermediate sequence type 276.

FIG. 1.

Population snapshot of 144 isolates from France (1992 to 2007), based on eBURST analysis. Each ST encountered is indicated by a circle, with diameters proportional to numbers of isolates (extracted from Table 1). The blue circle for ST276 corresponds to the founder of the clonal complex 276. The lines join single locus variants (SLVs). Two data sets were compared: a data set with the STs of the prevaccine period (1992 to 2002) and a data set with the STs of the vaccine period (2003 to 2007). STs are colored differentially depending on their membership in the two data sets: black (STs found only during the prevaccine period), green (STs found only during the vaccine period), or cyan (STs found during both periods). For ST276, the percentages of isolates before and during the vaccine period are indicated. Some STs of this study are related to STs of major clones described in the Pneumococcal Molecular Epidemiology Network (http://www.sph.emory.edu/PMEN) and indicative of potentially capsular switching. For each of these 10 STs, the name of the clonal type was indicated (e.g., Greece²¹-30). When a clonal type was related but not identical to an ST of this study, the degree of relatedness between them was specified (SLV or double locus variant [DLV]) and the ST no. of the clonal type was followed by an asterisk if it was not present in the study data set. ST320, ST202, and ST3259 are linked to the clonal type Taiwan^19F-14. However, ST202 and ST3259 could be considered relatives of ST320 in this context because it is known that ST320 already exists as a 19A serotype and it is more parsimonious to assume fewer cases of serotype switching.