Regional variation in ampicillin and trimethoprim resistance in Escherichia coli in England from 1990 to 1997, in relation to antibacterial prescribing

Over 200 hospitals in England report resistance data for bacteraemia and me ningitis isolates to the Public Health Laboratory Service. We reviewed ampi cillin and trimethoprim resistance rates from 1990 to 1997 for Escherichia coli, which is the species reported most frequently from these bacteraemias . Ampicillin resistance was relatively stable over time, but varied between Health Regions. The proportion of ampicillin-resistant E. coli in the East Anglia region remained less than or equal to 42% in all years except one a nd that in the South Western region always remained <50%. At the other extr eme, the proportions of ampicillin-resistant isolates in the Northern and T rent regions never fell below 59%. The prevalence of resistance to trimetho prim rose over time in most regions; again, however, the prevalence of resi stant isolates was lowest in the East Anglia and South Western regions, whe reas the highest resistance rates were reported from Mersey, NW Thames, NE Thames and North Western regions. These observations were related to data f or community prescribing, which accounts for most ampicillin and trimethopr im use. Prescribing data for ampicillin and trimethoprim from 1987 to 1997 were obtained from the IMS-HEALTH Medical Data Index, and data for all anti bacterial drugs between 1995 and 1997 from the Prescription Pricing Authori ty. Correlations between resistance rates and prescribing of specific antib iotics were weak, although there was some trend for regions with high total prescribing to have higher rates of ampicillin resistance. The South Weste rn region was conspicuous both for low rates of resistance and low prescrib ing. Several factors may determine the lack of wider and more obvious relat ionships between resistance and prescribing. In particular, regions may be inappropriately large areas to test the relationship, isolates from bactera emias may not be representative of those experiencing selection pressure in the community and the resistance data may have been distorted by nosocomia l strains, although this seems unlikely with E. coli.