Community antibiotic therapy, hospitalization and subsequent respiratory tract isolation of Haemophilus influenzae resistant to amoxycillin: a nested case-control study.

The study objective was to determine whether recent community antibiotic prescribing and hospitalization are associated with beta-lactam resistance in respiratory isolates of Haemophilus influenzae. Data obtained for hospitalization and community prescribing (in the previous 3 months) from 412 adults (>15 years) in whom an episode of respiratory tract infection had been described, during which H. influenzae was isolated, were analysed. Seventy-three (17.7%) isolates of H. influenzae were resistant to amoxycillin. Resistance was associated with recent hospitalization [odds ratio (OR) 3.2, 1.8-5.6] and antibiotic exposure in the community (2.1, 1.2-3.6). These variables were independently associated with amoxycillin resistance [hospitalization (OR 4.5, 1. 7-12.5) and community beta-lactam antibiotic exposure (3.9, 1.6-9. 8)]. Hospitalized patients probably received antibiotics during their admission although aquisition of the organism or the beta-lactamase via plasmids from other Gram-negative organisms in the hospital could also be a factor. Control measures to reduce the inappropriate use of antimicrobials in the community and in hospital need to be reinforced.