Influence of recent antibiotic therapy on antimicrobial resistance of Streptococcus pneumoniae in children with acute otitis media in Spain

Background. Despite the high prevalence of penicillin resistance among Streptococcus pneumoniae strains in Spain (40 to 60% with MIC greater than or equal to 0.1 mu g/ml), the data on acute otitis media (AOM) isolates are scarce. We conducted a prospective, longitudinal study to determine the rates of antimicrobial resistance of S. pneumoniae isolates from children with AOM in our country and to analyze the effect of previous antibiotic therapy on these rates. Methods. Tympanocentesis was performed on 169 children diagnosed with AOM (age range, 1 month to 14 years). Two groups were considered: Group A, 113 patients with non-antibiotic-treated AOM, subdivided into Group Al (collected from 1989 to 1992) and Group A2 (1992 to 1996); Group B, 56 patients from the period 1992 to 1996, with AOM clinical failure, defined as worsening or persistent symptoms after at least 2 days of appropriate antibiotic therapy, Amoxicillin-clavulanate was the most frequent antibiotic used (68%), followed by azithromycin (21%), cefaclor and cefixime (11%). Results. A total of 63 S. pneumoniae isolates were recovered, 42 in Group A and 21 in Group B. Resistance to penicillin (MIC greater than or equal to 0.1 mu g/ml) was found in 38% of strains in Group A (32% in Al and 50% in A2), but in Group B the rate of resistance reached 90% (P = 0.0002). Erythromycin resistance was also increased from 35% (Group A2) to 62% (Group B), and trimethoprim-sulfamethoxazole resistance rose from 64% to 81%. Conclusions. Resistance to penicillin among S. pneumoniae AOM isolates is frequent and is increasing in Spain. After failure of standard antibiotic: therapy, the rates of penicillin resistance reached 90% of the isolates.