Nasopharyngeal carriage and transmission of Streptococcus pneumoniae in American Indian households after a decade of pneumococcal conjugate vaccine use

Background: Young children played a major role in pneumococcal nasopharyngeal carriage, acquisition, and transmission in the era before pneumococcal conjugate vaccine (PCV) use. Few studies document pneumococcal household dynamics in the routine-PCV7 era. Methods: We investigated age-specific acquisition, household introduction, carriage clearance, and intra-household transmission in a prospective, longitudinal, observational cohort study of pneumococcal nasopharyngeal carriage in 300 American Indian households comprising 1,072 participants between March 2006 and March 2008. Results: Pneumococcal acquisition rates were 2-6 times higher in children than adults. More household introductions of new pneumococcal strains were attributable to children <9 years than adults >17 years (p<0.001), and older children (2-8 years) than younger children (<2 years) (p<0.008). Compared to children <2 years, carriage clearance was more rapid in older children (2-4 years, HR_clearance 1.53 [95% CI: 1.22, 1.91]; 5-8 years, HR_clearance 1.71 [1.36, 2.15]) and adults (HR _clearance 1.75 [1.16, 2.64]). Exposure to serotype-specific carriage in older children (2-8 years) most consistently increased the odds of subsequently acquiring that serotype for other household members. Conclusions: In this community with a high burden of pneumococcal colonization and disease and routine PCV7 use, children (particularly older children 2-8 years) drive intra-household pneumococcal transmission: first, by acquiring, introducing, and harboring pneumococcus within the household, and then by transmitting acquired serotypes more efficiently than household members of other ages.