Emergence of 13-Valent Pneumococcal Conjugate Vaccine (PCV13) Nonvaccine-Specific Streptococcus pneumoniae Serogroups 15, 23, 33, and 35 Isolated From Children in Kansas City, Missouri

Abstract

Background. The 13-valent pneumococcal conjugate vaccine (PCV13) was licensed in February 2010 for the prevention of pneumococcal disease in children. This study examines the frequency of pneumococcal serotypes isolated from children ages 1 week to 19 years in our institution, with particular focus on emerging PCV13 nonvaccine-specific serotype strains. Methods. Active pneumococcal surveillance was conducted at Children's Mercy Hospital in Kansas City, Missouri from 2011 through 2015. All pneumococci isolated from clinical specimens were serotyped by the Quellung capsular swelling reaction. Patient demographic and clinical data were abstracted from medical chart reviews. Duplicate samples were not included in analysis. Results. From 2011 through 2015, 427 pneumococcal clinical isolates were evaluated: 122 (29%) invasive and 305 (71%) non-invasive strains. The most common non- PCV13 serogroups identified were 15 (9%), 23 (not F) (10%), 33 (4%), and 35 (8%). The most common PCV13-related serotypes were 3 (8%), 19A (11%), and 19F (7%). Except for serotypes 19A and 19F, the annual number of isolates with these serotypes/ serogroups remained relatively stable. Serotype 19A decreased from 22 isolates (19% of the yearly total) in 2011 to 0 isolates in 2015. Surprisingly, the number of serotype 19F isolates increased from 5 (4%) in 2011 to 11 (13%) in 2015. Overall, 75% of non-invasive isolates and 61% of invasive disease isolates had capsule serotypes not included in PCV13. Serotypes 19A, 19F, 23 and 35 were often penicillin nonsusceptible. The remaining serotype isolates were usually penicillin susceptible. Invasive pneumococcal disease was much less likely to occur in the third quartile compared to other yearly quartiles (p < 0.01). Conclusion. PCV13 nonvaccine-specific Streptococcus pneumoniae serotypes cause a considerable number of infections in children, and continued surveillance of pneumococcal serotype distribution is important to guide the development of future pneumococcal vaccines.