Distribution of Streptococcus pneumoniae serotypes in isolates collected from sterile body sites in the United States (US), 2004-2015

Abstract

Background: Streptococcus pneumoniae remains a leading cause of disease in children and adults. Serotypes differ in invasiveness, virulence and antibiotic resistance; therefore, serotype surveillance is necessary to monitor the seroepidemiology of invasive pneumococcal disease. The serotypes and antibiotic susceptibilities of 2,105 S. pneumoniae isolates (from sterile body sites) collected in the US through the Tigecycline Evaluation Surveillance Trial, (TEST) 2004-2015, were evaluated. Methods & Materials: Serotypes were determined by PCR; isolates non-typeable by PCR were serotyped by the Quellung reaction. Minimum inhibitory concentrations were determined by broth microdilution and interpreted using CLSI guidelines. Results: In the US, in the 2010-2015 time period, serotypes 19A (27.3%), 35B (18.2%), 3 (9.1%), and 34 (6.8%) were the most common in children under 2 y. In adults ≥65 y, serotypes 19A (10.0%), 22F (8.2%), 23A (8.2%), 35B (7.8%), and 3 (7.3%) were most common. Overall, the proportion of isolates with PCV13 serotypes declined when comparing the pre-PCV13 and post-PCV13 time periods [Figure 1]. The proportion of isolates of serotype 19A that were penicillin-susceptible (PSSP) decreased in the post-PCV13 period (74.8% (2004-2009) compared to 44.6% (2010-2015)). However, the overall proportion of PSSP changed only modestly between 2004-2009 (92.5%) and 2010-2015 (91.2%). The proportion of erythromycin-resistant isolates increased in the later time period and shifted in serotype distribution, with the highest percentages found in serotypes 19A, 33F, 15A, 33A, and 35B in 2010-2015, compared to 15A, 9 V, 19F, 14, and 19A in 2004-2009. Conclusion: These data, although limited in numbers, demonstrate that vaccination of infants with PCVs has resulted in reductions in invasive disease caused by PCV7/13 serotypes, but some residual disease remains in all age groups. The 2014 recommendation to vaccinate all adults ≥65 with PCV13 was warranted to further reduce invasive disease in this age group. Susceptibility of S. pneumoniae to antimicrobial agents commonly used as part of empiric therapy further documents the value of vaccination programs and the need for ongoing monitoring of the seroepidemiology of this important pathogen.