- Background. Information on the causative agents of acute otitis media (AOM) in infants <2 months of age is limited. Objectives of the study. To analyze the etiology, pathogen susceptibility patterns, clinical presentation and frequency of serious bacterial infections in infants <2 months of age with AOM and to determine the relationship between the organisms isolated systemically and those isolated from the middle ear fluid in the patients with serious bacterial infections in the presence of AOM. Methods. The medical records of 137 infants <2 months of age with AOM who underwent tympanocentesis in the emergency room of Soroka University Medical Center between January 1, 1995, and May 30, 1999, were reviewed. The main variables analyzed included demography, frequency of serious bacterial infections, bacteriologic results, susceptibility patterns of the pathogens and clinical presentation. Results. Median age was 38.7 ± 13 days; 112 of 137 (82%) infants were hospitalized. Six (4%), 27 (20%), 46 (34%) and 58 (42%) episodes were recorded at age 0 to 2, 3 to 4, 5 to 6 and 7 to 8 weeks, respectively. Fever (temperature >38°C) was present in 96 (70%) of the cases. Culture-negative (bacterial) meningitis was diagnosed in 3 cases. Blood and urine cultures were positive in 1 and 6 infants, respectively. None of the afebrile infants developed serious bacterial infection. One hundred twenty-two bacterial pathogens were isolated from the middle ear fluid of 109 of 137 (80%) patients:Streptococcus pneumoniae in 56 (46%), Haemophilus influenzae in 41 (34%), group A Streptococcus in 12 (10%), enteric Gram-negative bacilli in 9 (7%), Moraxella catarrhalis in 3 (2%) and Streptococcus faecalis in 1 (1%). Eleven (20%) of the 56 S. pneumoniae isolates were nonsusceptible to penicillin. Serious bacterial infections were diagnosed in 6 of 137 (4%) patients. Whereas blood and urine grew pathogens typical for blood and urinary tract infections, the middle ear fluid isolates represented different pathogens usually isolated in AOM without any correlation between these 2 groups of pathogens. Conclusions. (1) Most cases of AOM in infants <2 months of age are caused by pathogens similar to those causing AOM in older children; (2) antibiotic resistance may already be present at early age and should be considered in the empiric treatment of AOM in infants <2 months of age; (3) the presence of AOM does not predict a higher risk for serious bacterial infections in afebrile and febrile infants <2 months of age.