Bacteriology of acute otitis media unresponsive to initial antimicrobial therapy.

To determine the microbiology of acute otitis media unresponsive to initial antimicrobial therapy, we performed tympanocentesis on 43 children. All had failed to improve after at least 36 hours of therapy. Initial therapy was ampicillin or amoxicillin (31), trimethoprim-sulfamethoxazole (5), erythromycin and sulfisoxazole (5), erythromycin (1), and ampicillin and gentamicin (1). Among these children, 19% had isolates from middle ear fluid resistant to initial therapy. Bacteria sensitive to initial therapy were isolated from ten children (24%). The majority of children (57%) had bacteriologically negative middle ear fluid. Resistant isolates from children initially treated with ampicillin or amoxicillin were sensitive to trimethoprim-sulfamethoxazole or to erythromycin and sulfisoxazole, and vice versa. Critically ill children should have tympanocentesis to guide therapy; other children who fail to respond to antimicrobial therapy may receive alternative therapy as indicated by the results of this study.