Journal
JOURNAL OF INFECTIOUS DISEASES
Volume 195, Issue 3, Pages 347-352Publisher
OXFORD UNIV PRESS INC
DOI: 10.1086/510249
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Funding
- AHRQ HHS [R01 HS10247] Funding Source: Medline
- NIAID NIH HHS [R01 AI066304, AI048935, AI48935] Funding Source: Medline
- NIDCD NIH HHS [R01 DC005855, DC005855] Funding Source: Medline
- Wellcome Trust [030662] Funding Source: Medline
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Background. In response to the selective pressure of pneumococcal conjugate vaccine, increased asymptomatic carriage of antibiotic-nonsusceptible nonvaccine serotypes (NVTs) has been observed. Possible mechanisms include de novo acquisition of resistance, serotype switching, introduction of new clones, and expansion of existing clones. Methods. To investigate the process of increased antibiotic nonsusceptibility among replacing serotypes, we applied multilocus sequence typing to samples of 126 and 222 pneumococci collected in 2001 and 2004, respectively, from the nasopharynges of children < 7 years of age in 16 Massachusetts communities. Results. We found no evidence of penicillin resistance due to either serotype switching or de novo acquisition. Nonetheless, resistance increased through the expansion of previously recognized clones of NVTs, particularly in serotypes 19A, 15A, and 35B. In 19A, several unrelated clones increased in frequency, whereas, in the other 2 serotypes, single resistant lineages were responsible for the increased prevalence of resistant strains. Conclusions. The decreased prevalence of antibiotic resistance with the introduction of heptavalent pneumococcal conjugate vaccine is likely to be partially eroded over time as vaccine-included serotypes are replaced by resistant clones of NVTs. The clinical significance of this will depend on the pathogenic potential of replacing clones to cause local (e.g., otitis media) or invasive disease.
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