Risk of resistance related to antibiotic use before admission in patients with community-acquired bacteraemia.

We analysed the association of antibiotic therapy before admission and antibiotic resistance of blood isolates in a total of 1717 community-acquired bacteraemias in the County of Northern Jutland during 1992-96. Antibiotics had been prescribed to 14% of the patients during the 30 days before admission and to 37% during the 6 months. The most frequently prescribed antibiotics within 30 days were ampicillin (28%), penicillin G (27%), sulphonamides and/or trimethoprim (16%) and macrolides (14%). The most frequent blood isolates were Escherichia coli (33%), other Enterobacteriaceae (8%), Streptococcus pneumoniae (23%) and Staphylococcus aureus (10%). Of the 575 isolates of E. coli, 425 (74%), 432 (75%) and 518 (90%) were susceptible to ampicillin, sulphonamides and trimethoprim, respectively. Previous antibiotic prescriptions were strongly associated with resistance to ampicillin, sulphonamides and trimethoprim in E. coli. The association was less pronounced for S. aureus and enteric rods other than E. coli. Antibiotic prescriptions within the last 3 months predicted antibiotic resistance, and this should be taken into account when selecting empirical antibiotic therapy of severe community-acquired infections.