Characterization of pneumococcal isolates before and after PCV7 vaccine introduction in Peruvian children Open Access

Law, Caitlin Shay (2014)

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Infection caused by Streptococcus pneumoniae is a major preventable global public health issue severely affecting young children, especially those in developing countries. The purpose of this project is to examine the effect of the rollout of the 7-valent pneumococcal conjugate vaccine (PCV7) on pneumococcal strains in response to vaccine introduction in developing countries, specifically isolates from Peru. This was done via comparison of serotypes and clonal complexes of 525 carriage isolates and 215 invasive isolates before and after vaccination.

We found a pre-PCV7 carriage rate of 24.73% (525/2123) and predominant serotypes for the carriage population were 19F (18.7%), followed by 6B (14.7%), 23F (9.1%), and 14 (6.9%). Antibiotic resistance was seen in mostly vaccine-type serotypes and 108 of 525 (20.6%) carriage isolates were multidrug resistant.Out of 214 isolates from cases of IPD, the predominant serotypes were 14 (20.9%), 6B (14.9%), and 19F (12.6%). Vaccine-type serotypes accounted for 66.95% of the invasive pneumococcal population. For the 2 years and under age group, the predominant serotype before PCV7 introduction was 14 and remained dominant after vaccination. In the over 2 age group, 23F was the predominant serotype before PCV introduction, and 19F became prevalent post-vaccination. Oxacillin non-susceptibility significantly changed (p=0.001) after vaccination in the under 2 age group, but there was no substantial change with resistance in any other antimicrobial class in either age group. Sequence type 156 was prevalent in both the carriage and invasive populations. 82 out of 208 (39.4%) isolates in the invasive population were global resistance-conferring PMEN clones, and 21.9% (114/521) of carriage isolates were PMEN clones.

Molecular epidemiology is an extremely useful tool for understanding population dynamics following the use of vaccines for control and prevention of S. pneumoniae infection. Future studies using whole genome sequencing would provide an increased level of sensitivity to further investigate these changes for vaccine evasion at a population level.

Table of Contents

Table of Contents

Abstract i

Cover Page ii

Table of Contents iii

List of Tables iv

List of Figures v

Background 1

Methods 8

Results 12

Discussion 17

Strengths and Weaknesses 21

Future Directions 23

References 25

Tables 31

Figures 37

Appendix A: Institutional Review Board Protocol Exemption Letter 42

Appendix B: Circulating PMEN clones and sequence types 43

Appendix C: Additional figures 44

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