USP and Its Implications for Measuring Microbial Recovery Rates

USP and Its Implications for Measuring Microbial Recovery Rates


Following the last blog, which discussed the specifics of chapter <1116>, we move on to discuss the Case for CRR in more depth.

This chapter emphasizes that if human operators are present, microbial contamination at some level is inevitable. The following points on the conventional way to evaluate microbial contamination are discussed:

  • Real-time active monitoring of Total Particulate, even if run continuously, does not provide direct information on the microbiological content of the environment.
  • Airborne microorganisms are enumerated as CFU, but a great diversity of physical states (single cells, aggregates associated to particles, microbial cells associated to inert particles, etc.) make the counts subject to significant variability.
  • A microbial monitoring sample represents only the microorganisms captured during a narrow length of time at a particular location.
  • The absence of growth on a microbiological sample means only that growth was not discovered. It does not mean that the environment is free of contamination.
  • Numerical differences between Alert and Action Levels have become quite small in ISO 5 and other areas.
  • Those differences are not significant considering the large variability in microbiological assay recovery (±0.5 log₁₀) (1).

Based partly on the above points, <1116> proposes a new perspective on environmental control relying on incident rates rather than Action/Alert Levels. The proposal emphasizes that “rather than isolated events, analysis of data upon time would detect changes in the contamination recovery rate (CRR) that may be indicative of changes in the state of control within the environment”. Because of the inherent variability of microbial sampling methods and the CFU values, recommends the use of CRR as a more useful measure of trending results than the number of colonies recovered from a given sample.

To read a case study, download the entire paper here.

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