We applied MLST to 267 non-vaccine type pneumococcal carriage and invasive disease isolates from Navajo and White Mountain Apache children from 2006 to 2008, and compared them to those from 1998 to 2000. Microarray was used to confirm capsule switching events.
The primary mechanism of ST replacement among Navajo and White Mountain Apache children was expansion of existing STs, although introduction of new STs was an important secondary mechanism. ST199, a majority being serotype 19A, was the most common ST in both eras. Only ST193 (serotype 21) was preferentially expanding in the PCV7 era. Three examples of capsule switching were identified. No variability in vaccine effectiveness by ST was observed.
We did not observe an influence of ST on PCV7 serotype-specific effectiveness, although some STs may be favored in replacement.