Distributions and Annual Changes of Streptococcus pneumoniae Serotypes Causing Infections in Adult Patients: Eight Years of US Surveillance (2009–2016)

BACKGROUND: A pneumococcal polysaccharide vaccine (PPSV23) has been available for use in adults ≥65 years old since 1983 with vaccination rates of ~65% in the past decade. A conjugate vaccine (PCV13) has been recommended for adults since 2014, and for children since 2010 (replaced PCV7 which was used since 2000). The serotype distribution of pneumococci causing infections in adult patients in the US was evaluated. METHODS: 6,491 S. pneumoniae isolates were collected from patients (≥18 years old) seen/hospitalized in 105 US centers and recovered primarily (77.8%; 5,052/6,491) from lower respiratory tract specimens. Identification was performed by biochemical algorithms and/or PCR. The cpsB sequence was obtained by PCR or next genome sequencing for serotype determination. Multiplex PCR and/or Quellung reaction were performed, as needed. RESULTS: 19F was the most prevalent PCV7 serotypes with annual rates of 1.6–3.1%, but no trends were observed for this serotype during the period. Overall, PCV13 serotype prevalence declined considerably from 38.6% in 2009 to 23.1% in 2016, but rates remained stable during 2013–2016 (21.5–24.6%). Serotype 19A (12.4%) and 3 (9.1%) were the most common PCV13 serotypes (2009–2016), followed by 7F (2.4%). Prevalence of 19A and 7F declined from 17.5% to 7.1% and from 4.6% to 0.7%, respectively, while the prevalence of serotype 3 remained stable. The proportion of non-vaccine serotypes increased, as did PPSV23 (non-PCV13). Among non-vaccine serotypes, 35B (8.1%), 23A (6.2%), and 6C/6D (5.8%) were the most common, followed by 23B (4.8%) and 15A/15F (4.8%). Prevalence of serotype 35B (from 3.9% to 12.6%) and 23B (from 3.7% to 7.8%) increased considerably during the study period. Serotypes 23A and 15A/15F remained stable throughout; however, serotype 6C/6D decreased from 7.6% to 3.4%. CONCLUSION: Prevalence of serotype 19F remained low and stable during the study period. PCV13 serotypes declined considerably, but serotypes 19A and 3 remained elevated. The consistent increase of non-vaccine serotypes, especially 35B, may be a reason for concern since it exhibits decreased susceptibility to β-lactams. Continued surveillance is needed to constantly assess the dynamic changes of serotypes affecting the adult US population. DISCLOSURES: R. E. Mendes, Pfizer, Inc.: Research Contractor, Research grant; H. L. Sings, Pfizer, Inc.: Employee, Salary; B. Hilton, Pfizer, Inc.: Employee, Salary; T. P. Doyle, Pfizer, Inc.: Research Contractor, Research grant; L. N. Woosley, Pfizer, Inc.: Research Contractor, Research grant; R. K. Flamm, Pfizer, Inc.: Research Contractor, Research grant; R. E. Isturiz, Pfizer, Inc.: Employee, Salary