Increased antimicrobial resistance in organisms recovered from otitis media with effusion

Previous studies concerning the microbiology of otitis media with effusion (OME) did not correlate the past use of antimicrobial agents with the recovered organism's antimicrobial susceptibility. A retrospective analysis of cultures obtained from aspirates of 129 children with OME was performed. The study identified the isolated organisms and determined their susceptibility to the most recently administered antimicrobials. Bacterial growth was noted in 58 (45 per cent) patients. Aerobic organisms only were recovered in 37 aspirates (63 per cent of the culture-positive aspirates); anaerobic bacteria in seven (12 per cent); and mixed aerobic and anaerobic bacteria in 14 (24 per cent). A total of 92 bacterial isolates were recovered, accounting for 1.6 isolates per specimen (1.1 aerobes and 0.5 anaerobes). There were a total of 66 aerobic isolates, including Haemophilus influenzae non type-b (20 isolates), Streptococcus pneumoniae (17), and Staphylococcus spp. (seven). Twenty-six anaerobes were recovered, including Peptostreptococcus spp. and Prevotella spp. (eight each) and Propionibacterium acnes (four). Resistance to the antimicrobial used was found in 60 (65 per cent) isolates, recovered from 41 (71 per cent) of the patients. Of the 41 patients in whom resistance was detected, 37 (90 per cent) had been treated within three months of culture and four (10 per cent) had completed treatment more than three months before the cultures were taken (p < 0.01). The highest rate of recovery of resistant organisms was following trimethoprim-sulfamethoxazole (96 per cent), amoxycillin (71 per cent), and azithromycin (56 per cent). Of the patients treated with amoxycillin, H influenzae predominated. S pneumoniae was recovered from four of the seven (57 per cent) after trimethoprim-sulfamethoxazole, four of 14 (29 per cent) following amoxycillin, and three of 11 (27 per cent) after azithromycin. The data illustrate the relationship between resistance to the antimicrobials given to children and their recovery from the middle ear of patients with OME.