Susceptibility statistical data, consisting of the cumulative and ongoing summary of the antimicrobial susceptibility patterns of clinically important microorganisms, are important to the practice of medicine on several levels. If the methods used to create, record, and analyze the data are not reliable and consistent, many of the most important applications and benefits of the data will not be realized. Clinical and Laboratory Standards Institute document M39—Analysis and Presentation of Cumulative Antimicrobial Susceptibility Test Data provides guidelines for medical laboratories and data analysis software providers for the routine generation and storage of susceptibility data and for the compilation of susceptibility statistics. This guideline also provides suggestions for medical laboratories, clinicians, and others involved in antimicrobial stewardship on effective use of their cumulative susceptibility statistics when empirical antimicrobial therapy is selected.

This guideline replaces the previous edition of the approved guideline, M39-A4, published in 2014. Several changes were made in this edition, including: • Adding definitions for "cumulative antimicrobial susceptibility test data report" and "antibiogram" • Adding considerations for extracting data from different sources (eg, automated antimicrobial susceptibility testing instrument, LIS, electronic health record) for antibiogram preparation • Combining results from rapid diagnostics and antimicrobial resistance marker testing with the antibiogram for empirical therapy selection • Developing antibiograms for yeast and antifungal agents • Developing antibiograms for multiple facilities, long-term care facilities, and veterinary practices • Describing ways in which antimicrobial stewardship programs may use antibiogram data • Adding considerations for preparing cumulative antimicrobial susceptibility test data for peer-reviewed publication • Using statistical analysis techniques including the calculation of percentiles, interquartile ranges, minimal inhibitory concentration (MIC) required to inhibit the growth of 50% of the organisms (MIC50), and MIC required to inhibit the growth of 90% of the organisms (MIC90) • Adding general comment explaining the use of the "^" with intermediate breakpoints for applicable antimicrobial agents known to have the ability to concentrate in the urine • Deleting recommendation to list percent intermediate in addition to percent susceptible for penicillin with viridans group streptococci

This guideline provides individuals involved with assessment of cumulative antimicrobial susceptibility test data with recommendations for the storage, analysis, and presentation of the data. The antimicrobial susceptibility test data from individual patient's isolates available for analysis are assumed to be final, accurate and in a usable format for health care providers. Recommendations cover the preparation of reports (eg, routine and enhanced antibiograms) to guide selection of empirical antimicrobial therapy. Reference to preparation of reports for other purposes is briefly discussed. This guideline is intended for use by individuals involved with: • Analyzing and presenting cumulative antimicrobial susceptibility test data generated from testing microbial isolates from both humans and animals from single or multiple facilities (eg, clinical microbiologists, pharmacists, physicians, veterinarians, epidemiologists, infection prevention practitioners) • Using antibiograms and other types of cumulative antimicrobial susceptibility test data to make clinical decisions, participate in antimicrobial stewardship programs, and/or participate in public health initiatives (eg, clinical microbiologists, infectious diseases specialists and other clinicians, infection prevention practitioners, pharmacists, epidemiologists, other health care personnel, and public health officials) • Designing information systems for the storage and analysis of antimicrobial susceptibility test data (eg, LIS vendors, electronic health record [EHR] vendors, manufacturers of diagnostic products that include epidemiology analysis software, and manufacturers of epidemiology analysis or surveillance software) This guideline does not include procedures for selecting isolates for antimicrobial susceptibility testing (AST), performing AST, interpreting AST results, nor confirming the accuracy of AST results.