Background: A pneumococcal polysaccharide vaccine (PPSV23) has been recommended for adults ≥65 years old (y/o) since 1997, with vaccination rates ~65% in the past decade. A conjugate vaccine (PCV13) had been recommended since 2014. The serotype (ST) distribution and susceptibility profiles of pneumococci causing infections in adult patients in the US prior to and after the PCV13 introduction (2009-2013) were evaluated.
Methods: 4,491 S. pneumoniae originated from patients (≥18 y/o) seen/hospitalized in 87 US centers. Isolates were recovered primarily (79.0%; 3,549/4,491) from lower respiratory tract specimens. Serotyping was performed by cpsB sequencing, multiplex PCR and/or Quellung. Susceptibility testing applied CLSI methods.
Results: PCV7 ST (4.6% - 4.9%) remained stable during 2009 - 2012, decreasing to 2.9% in 2013. 19F (62.4%, all years) represented the majority of PCV7 pneumococci with rates of 2.8%, 2.9%, 3.0% and 3.2% in 2009, 2010, 2011 and 2012, respectively, and declined to 1.7% in 2013. Overall, PCV13 comprised 31.1% of ST but declined from 38.5% in 2009 to 24.7% in 2013. Rates of 19A (15.0% - 17.5%) remained consistent in 2009 - 2011 and declined to 12.7% and 11.5% in 2012 and 2013, respectively. ST 6A decreased to 0.2% in 2013, whereas ST 7F increased from 4.6 to 5.5% during 2009 and 2010 before decreasing in the following years to 1.8%. ST 3 showed consistent rates (8.1% - 9.9%) over time. The proportion of non-PCV ST increased during the study period, as did PPSV23 (not PCV13). Among non-PCV, 23A (8.6%) was the most common ST in 2013, followed by 35B (7.3%), 11A/11D (6.3%), 22F/22A (6.0%), 15A/15F (5.5%) and 6C/6D (4.8%). The latter showed a decreased prevalence from 12.9% in 2009 to 6.6% in 2013, whereas 35B and 15B/15C rates increased during the four initial years but had lower rates in 2013. Overall, susceptibility rates for penicillin (MIC, ≤2 µg/ml; +3.0%) and tetracycline (+10.1%) increased between 2009-2010 and 2012-2013 periods.
Conclusion: PCV7 rates were stable during the four initial years before decreasing in 2013. PCV13 rates declined over time, mostly due to decreasing rates of 19A, 6A and 7F suggesting the presence of an indirect effect. Continued surveillance is needed to constantly assess the dynamic changes of ST affecting this older USA population.
R. E. Mendes,
H. Sings, Pfizer Inc.: Employee , Salary
R. K. Flamm, Pfizer Inc.: Research Contractor , Research grant
R. E. Isturiz, Pfizer Inc.: Employee , Salary