Microbiology of acute otitis media recently treated with aminopenicillins

Introduction. Sparse recent data are available in the United States regardi ng the pathogens of acute otitis media (AOM) most likely to be recovered fr om children recently treated with the two most frequently prescribed antibi otics, amoxicillin or amoxicillin/clavulanate (AMC). Methods. Of the 704 rural Kentucky children with culture-positive AOM who u nderwent a single tympanocentesis or culture of otorrhea between 1992 and 1 998, 96 pathogens were recovered from 90 children during therapy or within 7 days posttherapy with an aminopenicillin. Identification and susceptibili ty testing of AOM pathogens were performed by routine National Committee fo r Clinical Laboratory Standards methods. Results. Pathogens recovered from children with AOM recently treated (0 to 7 days) with amoxicillin (n = 38) and AMC (n = 58), respectively, were as f ollows: Haemophilus influenzae (beta-lactamase-negative), 16 and 29%; H. in fluenzae (beta-lactamase-positive), 11 and 22%; penicillin-susceptible Stre ptococcus pneumoniae, 26 and 12%; intermediately penicillin-nonsusceptible S. pneumoniae (PNSP), 20 and 10%; resistant PNSP 13 and 17%; Moraxella cata rrhalis (betalactamase-positive), 13 and 7%; and Streptococcus pyogenes, 3 and 2%. H. influenzae was also isolated from 8 (75%) of 12 children treated with high dose AMC (similar to 80 mg/kg/day amoxicillin component). Signif icantly fewer children recently treated with amoxicillin were otitis-prone than those given AMC (24% vs. 74%, P < 0.0001). Conclusions. The predominant pathogen recovered from children with AOM rece ntly treated with amoxicillin was S. pneumoniae (59%) rather than beta-lact amase-producing organisms (24%). H. influenzae was the predominant (51%) pa thogen, rather than PNSP (27%), recovered from children recently treated wi th AMC.