Methods: 1142 isolates were recovered, serotyped by Quellung and tested for susceptibility to antimicrobials by disk diffusion or Etest.
Results: Among the 1142 isolates, 52 different serotypes were found and 59 isolates were non-typeable (5%). The most common were serotypes 3 (13%), 11A (8%), 19F, 9N and 23A (5% each), 23B, 16F and 6C (4% each). There were strong variations in the proportion of some serotypes, suggesting that factors other than vaccine pressure could also impact on serotype prevalence.
Although a considerable number of isolates still expressed the additional serotypes included in PCV13 (addPCV13=200), the overall proportion of addPCV13 serotypes remained relatively stable in this time period. However, when comparing with the previous period (2012-2014), there was a significant decrease in the proportion of addPCV13 serotypes, from 22% to 17.7% (p=0.007). Serotypes included in PCV7 (11%, n=122) and the serotypes exclusively found in the 23-valent polysaccharide vaccine (30%, n=339) did not change significantly in 2015-2017. Non-vaccine types were expressed by 42% of the isolates (n=481) and their proportion was also stable throughout the study.
Overall, resistance did not change relative to 2012-2014, with 22% erythromycin resistance and 18% penicillin non-susceptibility.
Conclusion: After the introduction of PCV13 in the National Immunization Plan for children, a significant decrease in the proportion of PCV13 serotypes was noted in the adult population, although a considerable fraction of disease is still caused by vaccine serotypes. Moreover, non-vaccine serotypes are becoming important causes of NIPP, emphasizing the importance of continued surveillance studies.
M. Ramirez, Pfizer: Speaker's Bureau , Speaker honorarium . GlaxoSmithKline: Consultant , Consulting fee . Merck Sharp and Dohme: Consultant , Consulting fee .
J. Melo-Cristino, Pfizer: Grant Investigator and Speaker's Bureau , Research grant and Speaker honorarium . Merck Sharp and Dohme.: Speaker's Bureau , Speaker honorarium .