Epidemiology of Streptococcus pneumoniae Serogroup 6 Isolates from IPD in Children and Adults in Germany

Mark Van Der Linden,Ralf René Reinert,Nadine Winkel,Stephanie Russo Perniciaro,Aron Farkas,Sharon Küntzel,Matthias Imöhl,Bernard Beall

doi:10.1371/journal.pone.0060848

Abstract

This study presents serogroup 6 isolates from invasive pneumococcal disease (IPD) before and after the recommendation for childhood pneumococcal conjugate vaccination in Germany (July 2006). A total of 19,299 (children: 3508, adults: 15,791) isolates were serotyped. Serogroup 6 isolates accounted for 9.5% (children) and 6.7% (adults), respectively. 548 isolates had serotype 6A, 558 had serotype 6B, 285 had serotype 6C, and 4 had serotype 6D. Among children, serotype 6B was most prevalent (7.5% of isolates) before vaccination, followed by 6A and 6C. After the 7-valent pneumococcal conjugate vaccine (PCV7), the prevalence of serotype 6B significantly decreased (p = 0.040), a pattern which continued in the higher-valent PCV period (PCV10, PCV13). Serotype 6A prevalence showed a slight increase directly after the start of PCV7 vaccination, followed by a decrease which continued throughout the PCV10/13 period. Serotype 6C prevalence remained low. Serotype 6D was not found among IPD isolates from children. Among adults, prevalence of both 6A and 6B decreased, with 6B reaching statistical significance (p = 0.045) and 6A showing a small increase in 2011–2012. Serotype 6C prevalence was 1.5% or lower before vaccination, but increased post-vaccination to 3.6% in 2011/12 (p = 0.031). Four serotype 6D isolates were found post-PCV7 childhood vaccination, and two post-PCV10/13. Antibiotic resistance was found mainly in serotype 6B; serotype 6A showed lower resistance rates. Serotype 6C isolates only showed resistance among adults; serotype 6D isolates showed no resistance. Multilocus sequence typing showed that sequence type (ST) 1692 was the most prevalent serotype 6C clone. Thirty-two other STs were found among serotype 6C isolates, of which 12 have not been previously reported. The four serotype 6D isolates had ST 948, ST 2185 and two new STs: 8422 and 8442. Two serogroup 6 isolates could not be assigned to a serotype, but had STs common to serogroup 6.

Highlights

Streptococcus pneumoniae remains a major cause of infectious disease globally, especially in children
A general recommendation for childhood pneumococcal conjugate vaccination was issued in Germany in July 2006
In this paper we evaluated the effects of this vaccination recommendation on invasive pneumococcal disease caused by serogroup 6

Summary

Introduction

Streptococcus pneumoniae remains a major cause of infectious disease globally, especially in children. Invasive pneumococcal disease (IPD) causes an estimated 0.5 million deaths among children worldwide [1]. 94 capsular types, or serotypes, have been described. Before the introduction of pneumococcal conjugate vaccination, serogroup 6 was one of the most common causes of IPD among children andadults. A new serotype, serotype 6C, could be identified among isolates previously typed as 6A. In serotype 6C, the capsular locus of the wciNa gene has been replaced through homologous recombination by the wciNb gene [2]. Serogroup 6 contains four serotypes, with serotype 6A having the wciPa gene and the wciNa gene, 6B (wciPb, wciNa), 6C (wciPa, wciNb) and 6D (wciPb, wciNb) [7]

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