Antimicrobial Susceptibility Testing (AST) Reporting
One of the five key Challenges to Integrated Surveillance.
Problem
Results from antimicrobial susceptibility testing are often reported only as S/I/R classifications (susceptible, susceptible with increased exposure, resistant) without the underlying quantitative data. This loses valuable information on resistance trends.
Why This Matters
EUCAST breakpoints are updated regularly as scientific evidence evolves. When breakpoints change:
- Historical data interpreted under previous breakpoints are no longer directly comparable with current data
- If only S/I/R interpretations are stored (not raw MIC or disk zone diameter data), retrospective re-analysis is impossible
- Breakpoints are increasingly defined for specific clinical entities (UTIs, meningitis, endocarditis), meaning interpretations depend on clinical context
Additionally, in animal surveillance, epidemiological cut-off values (ECOFFs) are used instead of clinical breakpoints, creating another layer of complexity.
Proposed Solution
Implement a policy for storing raw MIC (minimum inhibitory concentration) and disk zone diameter data in national databases.
Benefit
- Preserves granularity of resistance data
- Allows reclassification if breakpoints change
- Provides richer insights into emerging resistance patterns
- Enables consistent trend monitoring over time