Molecular epidemiology of pediatric pneumococcal empyema from 2001 to 2007 in Utah

Abstract

Utah had a high rate of pediatric pneumococcal empyema (PPE) prior to licensure of the pneumococcal conjugate vaccine (PCV-7) in 2000. The majority (62%) of PPE cases was due to nonvaccine serotypes, primarily Streptococcus pneumoniae serotype 1, multilocus sequence type (MLST) 227. PPE in Utah children has increased over the last decade. It is unclear whether the increase was due to serotype replacement or switch. In this study, we describe the incidence and molecular epidemiology of PPE by MLST in Utah children after the licensure of PCV-7. Empyema rates increased from 8.5/100,000 children in the state of Utah in 2001 to 12.5/100,000 children in 2007 (P = 0.006). Ninety-eight percent was due to nonvaccine serotypes (P < 0.001 when compared to the pre-PCV-7 period). PPE was primarily due to serotypes 1, 3, 19A, and 7F, with MLST demonstrating sequence types (ST) that were commonly present in the United States prior to licensure of PCV-7. Serotype switch was not documented. Replacement disease with common ST of serotypes 1,3, 7F, and 19A rather than serotype switch was responsible for the increase in PPE in Utah children.

FIG. 1.

(A) eBURST “population snapshot” showing the clusters and unlinked ST of the Streptococcus pneumoniae isolates of serotypes 1, 3, and 19A included in this study. The numbers indicate the ST-serotype designations. (B) eBURST diagram depicting the serotype 1 isolates in this study and related ST available in the MLST database (http://www.mlst.net) hosted at Imperial College London. Circle sizes demonstrate the relative prevalence of each ST in the database. Lines indicate one allele difference between connected circles. A predicted founder ST is in the center of a group and SLV radiate from the founder.