Epidemiology of acute otitis media caused by Streptococcus pneumoniae before and after licensure of the 7-valent pneumococcal protein conjugate vaccine.

We studied, by pulsed-field gel electrophoresis, multilocus sequence typing and penicillin-binding protein 2b amplicon-restriction profiles, pneumococcal isolates recovered from children with acute otitis media during 1 January-31 December 1999 and 2001. The proportion of nonvaccine serogroups increased from 14.8% (13/88) to 36.5% (23/63) from 1999 to 2001 (P<.01). Among children who received at least 2 doses of the pneumococcal 7-valent protein conjugate (PNC7) vaccine, 46.7% (7/15) of the isolates had nonvaccine serogroups, compared with 20.8% (26/125) of the isolates from children who did not receive the PNC7 vaccine (P=.05). Overall, the serogroups involved in capsular switching were 6-19-NT, 6-14-35, 15-19, and the 19-Spanish 23F clone. In 1999 and 2001, 30.8% (4/13) and 26.1% (6/23) of the nonvaccine serogroups were implicated in capsular switching, respectively. Continued surveillance will be of great importance as the distribution of the PNC7 vaccine increases.