Microbiology of acute otitis media in Costa Rican children

Because of the increasing number of resistant middle ear pathogens reported from different centers worldwide, an active surveillance of the microbiology and susceptibility pattern of middle ear pathogens is required for proper antimicrobial recommendations among different regions of the world.

To study the microbiology and susceptibility pattern of middle ear pathogens obtained from Costa Rican children with acute otitis media.

Between 1992 and 1997 a diagnostic tympanocentesis was performed in 398 Costa Rican patients with acute otitis media. Middle ear fluid was obtained for culture and minimal inhibitory concentrations were determined by the E-test technique in those isolates obtained between October, 1995, and January, 1997.

The most common pathogens cultured were Streptococcus pneumoniae (30%), Haemophilus influenzae (14%), Staphylococcus aureus (4%) and Streptococcus pyogenes (4%). Moraxella catarrhalis was uncommon. Beta-lactamase production was low (3.7%) among the H. influenzae isolates but frequent among the Staphylococcus aureus (57.1%) and M. catarrhalis (100%) strains. Overall 9 of 46 S. pneumoniae isolates (19.6%) exhibited decreased susceptibility to penicillin of which 8 isolates (17.4%) showed intermediate and one strain (2.2%) high level resistance. Among the penicillin-susceptible S. pneumoniae isolates, susceptibility to the following antimicrobials was: 81%, azithromycin; 89%, clarithromycin; and 100%, ceftriaxone and trimethoprim-sulfamethoxazole (TMP-SMX). Among the penicillin-resistant S. pneumoniae isolates the percentage of susceptible strains was 89% for azithromycin, clarithromycin and ceftriaxone and 67% for TMP-SMX.

Based on this microbiologic information the agents considered first line drugs in the treatment of acute otitis media in Costa Rica remain amoxicillin or TMP-SMX.