Non-PCV7 now causing AOM at prevaccine levels

Issue: May 2010

Acute otitis media and nasopharyngeal colonization rates related to nonvaccine-type Streptococcus pneumoniae have increased to levels similar to those seen during the pre-vaccine era, recently published study data indicate.

“This prospective study evaluated the [middle ear fluid] isolates and [nasopharyngeal] colonization patterns from PCV7-vaccinated (Prevnar, Wyeth) children 6 to 8 years after the introduction of PCV7 vaccine in the United States and compared the microbiology of AOM and [nasopharyngeal] colonization between their first or second AOM episode, and with children who are otitis prone,” Michael E. Pichichero, MD, an Infectious Diseases in Children editorial board member, and colleagues wrote.

The researchers enrolled 120 children who were aged 6 months and had no prior AOM and followed the children through 30 months of age. Researchers collected nasopharyngeal and oropharyngeal samples and tested middle ear fluid with tympanocentesis.

The researchers also included a second group of 80 children who experienced three AOM episodes in six months or four episodes in 12 months in their analysis. These otitis-prone children were aged younger than 36 months.

ll 200 children received appropriate doses of PCV7, according to the researchers.

Results revealed that only 0.9% of PCV7 serotypes were isolated from nasopharyngeal and middle ear fluid samples in both groups. The researchers noted, however, that prevalence of non-PCV7 serotypes was on par with that of non-typeable Haemophilus influenzae — the most common AOM isolate from 2001 to 2003. Moraxella catarrhalis and Staphylococcus aureus were low in both study cohorts.

Oxacillin-resistant S. pneumoniae isolated from nasopharyngeal and middle ear fluid samples was 19% for the absent/infrequent AOM group and 58% for the otitis-prone group (P<.0001), according to the researchers, although proportions of S. pneumoniae, non-typeable H. influenzae and M. catarrhalis were the same in both populations.

“In this current report, we described that the proportion of [S. pneumoniae] causing AOM has surged back to equal that of [non-typeable H. influenza] in otitis-prone children due to increasing AOM caused by non-PCV7 serotypes. The consequences of the anticipated introduction of an expanded pneumococcal vaccine, PCV13, should have a favorable, immediate and positive impact in reducing the most common non-PCV7 serotypes, especially 19A,” the researchers wrote.

Casey JR. Pediatr Infect Dis J. 2010;29:304-309.

Drs. Casey, Adlowitz and Pichichero have provided valuable information about otopathogens prior to and following the introduction of PCV7. The group’s latest publication identifies a marked decrease in AOM due to vaccine-type strains of S. pneumoniae but replacement by non-vaccine strains.

The result is that S. pneumoniae has regained its prominence as a cause of AOM — about equivalent to AOM due to non-typeable strains of H. influenzae. We know how the conjugate vaccines protect against invasive pneumococcal disease, and we have information about the concentration of antibody needed for protection.

We know far less about how PCV 7 protects against vaccine-serotype AOM. Perhaps the patient needs more antibody to prevent AOM than is necessary to protect against invasive pneumococcal disease. Are there surrogate immune markers that could be used to anticipate the efficacy of a new vaccine?

The availability of PCV13 raises questions about protection against new episodes of pneumococcal AOM. Will the availability of PCV13 result in a similar experience: decreased vaccine serotype pneumococcal AOM followed by replacement by non-vaccine serotypes, diminishing the overall benefit of the vaccine in decreasing the incidence of AOM? There is still a lot to learn about the immunology of the middle ear.

– Jerome O. Klein, MD
Infectious Diseases in Children Editorial Board

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