Background Pneumococcal conjugate vaccine (PCV7) is directed against the 7 most common serotypes of Streptococcus pneumoniae (Sp) causing invasive diseases. It has potential coverage for 57-85% of Sp serotypes causing acute otitis media (AOM). PCV7 reduces AOM incidence by 6-8% and reduces Sp- AOM by 34%. PCV7 may prevent AOM through reduction of nasopharyngeal (NP) colonization of vaccine serotypes of Sp; studies have shown this finding in healthy infants after PCV7 vaccination. No study compares NP bacterial colonization during AOM in the pre- and post-PCV7 vaccination eras.
Methods Children (6 mos.-6 yrs) were enrolled in AOM studies between 9/95 and 5/04. NP swab was obtained at the diagnosis of AOM. Bacterial cultures were performed by standard methods; Sp isolates were not serotyped.
Results Of 439 subjects, 215 were enrolled prior to PCV7 availability (historical controls); 224 were enrolled after PCV7 licensure: 126 of these were considered underimmunized, 98 were adequately immunized. Overall, Sp was isolated from 49% of cases, nontypeable H. influenzae (NTHi) from 34% and M. catarrhalis (Mc) 60%. NP colonization rate for Sp was not different between the 3 groups. (table)
There was no difference in penicillin-resistant Sp (PR-Sp) between groups, but there was a yearly trend for reduction in number and rate of colonization with PR-Sp in children diagnosed during the PCV 7 era. Colonization with NTHi tended to increase in PCV7 immunized children (p = .19). Colonization with Mc was significantly higher in immunized children (p = .0259). Combining 3 bacteria for each case, the mean number of bacteria in immunized children was significantly higher than controls (p = .05).
Conclusion In children with AOM, immunization with PCV7 did not reduce Sp colonization in the NP, although there was a trend for reduction in rates of PR-Sp. Increase in colonization by NTHi and Mc resulted in increased overall NP colonization with pathogenic bacteria. The clinical significance of this finding deserves further investigations.