Once you determine your sampling plan (see blog post “Microbial Environmental Sampling: Developing an Air and Surface Sampling Plan”) you are ready to sample, incubate, record, and EVALUATE your results. Remember, once you have determined your facilities ideal sampling plan, you aren’t going to change it up much unless your workflow changes significantly. The only “true” way to track and trend your data is to have the same data points upon each sampling.
Before we continue, just a tip on physically conducting sampling and incubation: The 2021 USP <797> revision gives word-for-word direction for these processes. This is also a great resource for developing a thorough SOP on conducting sampling.
Synopsis
EVALUATION of data consists of:
Identification of microbial growth to assess if you have recovered any “objectionable” organisms (continue reading for more information)
Assessment of each microbial sample to determine if any one or more sample(s) has exceeded the “allowable” limits of growth (aka Action Levels)
Once this has been done, the pass/failure status of one or more samples will give direction to next steps:
Pass = Document growth for each location in a spreadsheet so that you can easily track and trend your data for future needs
Failure = Time to act by investigation, remediation and eliminate the source. This is where many get stumped and will be discussed in a future blog post: Microbial Environmental Sampling: Investigation, Remediation and Elimination of Failed Air/Surface Samples.
Evaluation of Data
This is straight forward if you know what will result in a pass/failure. Your sample will result in a failure under the following circumstances:
You exceed “action limits” established by USP <797> and outlined in the chart below
Your grow “objectionable” organisms that are highly pathogenic and include, but not limited to, the following:
a. Gram negative rods
b. Coagulase-Positive staphylococcus (coagulase-negative staph. is allowable)
c. Yeast
d. Mold
e. Fungus
Remember, per current 2008 version of USP <797>, your lab* must measure growth in “colony forming units” (CFU) and identify every CFU to the genus level. The new 2021 revision will remove the requirement to identity to the genus level UNLESS growth exceeds the action levels stated in USP <797>.
Once results are identified to the genus level, you will evaluate if any of the highly pathogenic “objectionable” organisms mentioned above have been grown. If you recover just one CFU of an objectionable organism, you must mark the sample as a failure and immediately investigate, remediate, and eliminate the source (again remembering once the new 2021 revision of USP is accepted, identification will not be required unless you exceed the action levels set by USP).
If no “objectionable” organisms are recovered, then it is as straight forward as following the action level chart in USP <797>. A simplified version of this chart for air and surface samples appears below. If one or more samples exceed the limits indicated, the sample fails and it is time to investigate, remediate and eliminate the source that caused the failure.
That’s it for EVALUATION of results! Now you are ready to place your results in a spreadsheet to track and trend results against other samplings and for future evaluation.
INVESTIGATION of failed results will be addressed in a new blog post (Microbial Environmental Sampling: Investigation, Remediation and Elimination of Failed Air/Surface Samples). This topic can be difficult for some since we are dealing with microorganisms that are not visible with the naked eye. However, there are key principles that can help lead the investigation to identification of the source. This will be addressed in our next post!
Remember: It is not a question of IF you fail but rather WHEN you fail. The key is to know how to manage your investigation, documentation and what to do in between action and resolve to keep patients safe.
*As a side note on your lab identifying these organisms: If you have a good environmental USP compliant lab, they will most likely call to your attention any “objectionable” organisms. However, not all labs will do this, so that requires us to do our research on every organism with which we are not familiar to ensure that it is not one of these highly pathogenic objectionable organisms.
**Note the figure highlighted in RED represents a change in the surface sampling action level for ISO 8 areas in the proposed 2021 USP <797> revision. The publication of this blog post is prior to the implementation of the revision, therefore, may change with the release of the new standard. Always refer to the most current version of USP <797> to get the most up-to-date action levels. Additionally, if documented in the facility’s SOPs, you can assign more restrictive action levels than those presented in USP <797>.
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