Pneumococcal Carriage and Invasive Disease in Children Before Introduction of the 13-valent Conjugate Vaccine: Comparison With the Era Before 7-valent Conjugate Vaccine

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Background:Nasopharyngeal (NP) carriage and invasive pneumococcal disease (IPD) attributable to serotypes in the 7-valent pneumococcal conjugate vaccine (PCV7) declined dramatically after vaccine introduction, whereas non-PCV7 serotypes increased modestly. Characteristics of pneumococcal carriage and IPD among children in Atlanta, GA, were compared during 2 time periods: before PCV7 introduction and before 13-valent PCV (PCV13) introduction.Methods:NP swabs from 231 and 451 children 6–59 months old receiving outpatient medical care were obtained in 1995 and 2009, respectively. A total of 202 and 47 IPD cases were identified in children younger than 5 years of age in 1995 and in 2008 to 2009, respectively, through active, population-based surveillance in Atlanta. Isolates were serotyped, sequence-typed (ST) and tested for antimicrobial susceptibility.Results:Forty percent (93/231) of children in 1995 and 31% (139/451) in 2009 were colonized with Streptococcus pneumoniae; 60% and 0.7% were PCV7 serotypes, respectively. In 1995, PCV7 serotypes accounted for 83% and 19A accounted for 5% of IPD compared with no PCV7 serotypes and 19A accounting for 49% of IPD in 2009 (P < 0.001). In 2009, PCV13 serotypes accounted for 22% of carriage (mostly 19A) and 60% of invasive isolates (P < 0.001). ST320 accounted for 66% and 52% of 19A carriage and IPD isolates in 2009, respectively; all ST320 isolates were multidrug-resistant. No ST320 NP or IPD isolates were identified before PCV7.Conclusions:Serotype distribution among NP and IPD isolates in Atlanta has shifted to non-PCV7 serotypes; 19A was the leading serotype for both. The multidrug-resistant ST320 strain was responsible for two-thirds of 19A carriage isolates and half of IPD isolates. The predominance of serotype 19A in carriage and IPD among children in Atlanta highlights the potential direct and indirect benefits anticipated by implementation of PCV13 in the community.

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