INTRODUCTION: Acute otitis media (AOM) is the most common microbial respiratory tract infection in early childhood: Streptococcus pneumoniae is a common pathogen isolated from patients with AOM. The American Academy of Pediatrics advises immunization with a 7-valent pneumococcal conjugate vaccine for children with recurrent AOM.

OBJECTIVE: We aimed to establish the most common S pneumoniae serotypes present in the middle-ear fluid of Mexican children with AOM and to analyze antimicrobial susceptibility patterns and assess the potential protection provided by the new conjugated S pneumoniae vaccines.

METHODS: During 2002 and 2003, 72 S Pneumoniae isolates were obtained from 138 Mexican children with AOM. Serotyping distribution was performed by the quellung reaction with antisera from Statens Serum Institute (Copenhagen, Denmark). Tests for susceptibility were performed by using the agar-dilution method according to Clinical and Laboratory Standards Institute protocol for 18 antibiotics.

RESULTS: The most common S pneumoniae serotypes isolated were 6B and 19F (16.67% each) and 6A, 14, and 23F (15.27% each). The overall rate of resistance (defined as the rate of intermediate resistance plus the rate of resistance) for penicillin was 65.38% (intermediate and resistant categories were 29.17% and 36.11%, respectively), for cefotaxime was 19.45%, for azithromycin and erythromycin was 23.61%, for trimethoprim/sulfamethoxazole was 61.11%, for amoxicillin was 5.5%, and for clindamycin was 12.5%. With amoxicillin/clavulanate, ceftriaxone, imipenem, meropenem, teicoplanin, telithromycin, and vancomycin, we found susceptibility for 100% of the isolates. The most common resistant serotypes were 19F and 23F.

CONCLUSIONS: The serotype distribution of S pneumoniae that causes pediatric AOM in Mexico is similar to that reported from developed countries. The current heptavalent pneumococcal conjugate vaccine covers 63.89% of AOM episodes in Mexican children.

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