Survey, laboratory and statistical methods for the BSAC Resistance Surveillance Programmes.

The British Society for Antimicrobial Chemotherapy (BSAC) Bacteraemia and Respiratory Resistance Surveillance Programmes are designed for long-term surveillance of antimicrobial resistance in key pathogens of bloodstream and community-acquired respiratory infection in the UK and Ireland. This paper describes their methods in detail. Sentinel laboratories across the UK and Ireland contributed up to a fixed quota of isolates of defined bacterial groups. Collecting laboratories were compared with national benchmarks for size of Hospital Trust and distribution of bacteraemia pathogens. A central laboratory for each programme confirmed the identification of isolates, measured MICs by the BSAC agar dilution method and undertook further testing by standard methods. The variability of the MIC method was assessed by repeated annual testing of a panel of control isolates. Classification as susceptible, intermediate or resistant was by BSAC and European Committee on Antimicrobial Susceptibility Testing breakpoints. Statistical analysis was adjusted for inter-centre variation using random effects logistic regression. Thirty-two laboratories contributed 16 550 respiratory isolates from 1999-2000 to 2006-07; 30 laboratories contributed 15 812 bacteraemia isolates from 2001 to 2006. Although large and teaching hospitals were over-represented, the pattern of bacteraemia organisms seen in the collecting laboratories in England and Wales was similar to that in national data reported to the Health Protection Agency. Replicate MIC measurements showed that >/=90% agreed within +/-1, and >/=98% within +/-2, doubling dilutions. These surveillance programmes have provided reliable information on antimicrobial susceptibility in the UK and Ireland over six and eight seasons, respectively, so far. Detailed results showing non-susceptibility trends, and relationships with potential predictive factors, are presented in six linked papers in this Supplement.