- Objective. To determine the relation between early bacteriologic eradication and clinical outcome of acute otitis media (AOM) in infants and young children treated with various antibiotics. Study design. The study group consisted of patients ages 3 to 24 months seen at the Pediatric Emergency Room with: (1) symptoms and physical findings consistent with AOM of ≤7 days duration; (2) no spontaneous perforation or tympanostomy tubes; (3) positive initial middle ear fluid culture; and (4) a follow-up to at least Day 10 ± 2 of the study with a second culture performed 72 to 96 h after initiation of antibiotic treatment. Any patient with a positive middle ear fluid culture 72 to 96 h after initiation of antibiotic treatment was considered to have bacteriologic failure. Otologic evaluation was done by an otolaryngologist unaware of the culture results and of the study drug allocation. A clinical score based on body temperature, report of irritability and ear tugging observed by the parents and the appearance and redness of the ear drum as observed by the otolaryngologist was also used for clinical evaluation. Results. The study group consisted of 123 patients, of whom 57 (46%) had positive middle ear fluid 72 to 96 h after initiation of antibiotic treatment. Clinical failure was observed in 21 of 57 (37%) patients in whom bacteriologic eradication did not occur vs. only 2 of 66 (3%) patients with bacteriologic eradication after 3 to 4 days of treatment (P < 0.001). Clinical score for both moderate and severe disease decreased significantly faster in those with bacteriologic eradication than in those in whom middle ear fluid was still culture-positive 72 to 96 h after initiation of treatment. Conclusion. Clinical failures in our population were associated with inability to eradicate the causative organisms of AOM from the middle ear fluid within 3 to 4 days after initiation of antibiotic therapy. Most patients (including those without bacteriologic eradication) improved after 3 to 4 days of treatment, but patients with sterile middle ear fluid felt better after 3 to 4 days of treatment than patients in whom middle ear fluid was still culture-positive.