Abstract

We prospectively tabulated all isolates of Haemophilus influenzae at DeKalb Medical Center from 1987 through 1989 to assess the occurrence of antibiotic resistance in patients of different ages. Of 325 total strains isolated, 24% produced β-lactamase, rendering them resistant to ampicillin and amoxicillin. Antibiotic resistance was as common in patients older than age 60 (24%) as in younger patients (23%). Sensitivity testing by disk diffusion and microdilution techniques on 71 isolates (37 β-lactamase-positive) showed uniform susceptibility to cefuroxime, cefotaxime, amoxicillin/clavulanate, cefaclor, and chloramphenicol, but three β-lactamase-positive isolates were resistant to trimethoprim/sulfamethoxazole. The high rate of ampicillin resistance noted in elderly patients has implications for the choice of antimicrobial therapy for these infections.