June 23, 2014
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Serotypes 15, 35B prevalent among PCV13-vaccinated children with AOM

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Recent data showed unpredictable changes in nasopharyngeal pneumococcal colonization among children who received the 13-valent pneumococcal conjugate vaccine.

Judith M. Martin, MD, of the Children’s Hospital of Pittsburgh of the University of Pittsburgh Medical Center, and colleagues assessed nasopharyngeal cultures of 228 children, aged 6 to 23 months, who presented with a new episode of acute otitis media and were enrolled in an ongoing trial of antimicrobial efficacy. All children had received at least two doses of PCV13 (Prevnar13, Pfizer) and 90% had received three or more doses. Streptococcus pneumoniae isolates were serotyped and tested for antimicrobial susceptibility. Researchers compared findings with results obtained in three previous studies.

Judith M. Martin, MD 

Judith M. Martin

S. pneumoniae was found in half (113 of 228) of the study cohort. PCV7 (Prevnar, Pfizer) serotypes accounted for 2% of pneumococcal isolates (2 of 113), whereas PCV13 serotypes accounted for 12% (14 of 113). Of the 14 PCV13 serotypes, eight were serotype 19A.

Non-vaccine serotypes accounted for 69% (78 of 113) of pneumococcal isolates. Of these, 33% (26 of 78) were serotype 15, and 13% (10 of 78) were serotype 35B. Serotype 15 accounted for 23% (26 of 113) of pneumococcal isolates and serotype 35B accounted for 9% (10 of 113).

Of the 113 pneumococcal isolates, 37 were penicillin-non-susceptible; 23 were penicillin-intermediate; and 14 were penicillin-resistant. Serogroups 15 and 35B accounted for 49% of penicillin-non-susceptible isolates. Seventy percent of the 35B isolates had a penicillin minimum inhibitory concentration of 2 g/mL and ceftriaxone MIC of 1 g/mL. Six isolates of serotype 19A had a penicillin MIC at least 4 g/mL.

A similar percentage of children exhibited S. pneumoniae when diagnosed with AOM among the four cohorts included in this study. The overall percentage of non-susceptible isolates did not differ with time between cohorts. However, the proportions of PCV7 serotypes declined with time.

“It seems concerning that in [this study cohort] the newly emergent serotypes 15 and 35B not only predominated among the non-vaccine serotypes recovered, but also accounted for 49% of the pneumococcal isolates that were penicillin-non-susceptible. Among these non-vaccine serotypes, particularly concerning were the serotype 35B isolates, all of which were penicillin-non-susceptible. On the other hand, the overall proportion of pneumococcal isolates that were penicillin-non-susceptible appears not to have increased over time. … Continued surveillance will be required to monitor the effect of PCV13 on the burden of pneumococcal disease, and to monitor [nasopharyngeal] colonization as a potential marker of AOM and [invasive pneumococcal disease] pathogens and as a potential guide in planning vaccine modifications,” the researchers concluded.

Disclosure: For a full list of researchers’ financial disclosures, see the study.