Clones of Streptococcus pneumoniae isolated from nasopharyngeal carriage and invasive disease in young children in central Tennessee

To determine whether nasopharyngeal carriage isolates of Streptococcus pneumoniae are of the same genetic background as isolates that caused invasive disease in one community, IS1167 and boxA genotypes were obtained for 182 pneumococcal isolates from children living in central Tennessee. The isolates represented 70 combined IS1167-boxA genotypes. The genotypic diversity of the invasive isolates was significantly less than that of the total population ( ). Most of the carriage isolates belonged to genotypes unique to carriage, whereas P p .003 most of the invasive isolates belonged to genotypes common to carriage and disease (P p ). Monte Carlo simulations showed a greater number of genotypes unique to carriage than .02 can be explained by chance ( in all cases). Two genotypes were identified by multilocus P ! .05 sequence typing as members of globally disseminated clones, and one such genotype that was strictly carriage in this sample caused disease in other studies. Thus, clones can have different propensities for carriage and invasion. Streptococcus pneumoniae can be carried asymptomatically in the human nasopharynx, but little is known about the clones involved in carriage and their genetic relationships to clones associated with invasive disease. Invasion is correlated with at least transient carriage [1, 2]. Several studies have reported a link between carriage of pneumococci and the occurrence of acute otitis media [3–5]. Moreover, carriage isolates can exhibit the same capsule serotypes and genetic backgrounds as invasive isolates. For example, in a study by Takala et al. [6], the serotype 7 and 14 pneumococci were mostly clonal and invasive; however, there were 2 carriage isolates each of serotypes 7 and 14, and these belonged to the same genotypes as the isolates from disease. In a