Viable Sampling Challenges and Limitations
As you are well familiar with, USP General Chapter <797> currently requires viable air sampling every 6 months and surface sampling “periodically.” By default, many are collecting viable surface samples every 6 months as well. It just makes sense, right? Plus, nobody knows what periodically means anyway. But as we prepare for the release of a new version of the chapter, sampling frequencies will increase. Those preparing Category 1 and 2 preparations will be required to collect viable air samples every six months and surface samples monthly, while those preparing Category 3 preparations will be required to collect viable air samples monthly and surface samples weekly, and at the end of every batch prepared. This increased sampling frequency will likely result in more excursions and microbial investigations.
As you potentially face more excursions, there are few viable sampling challenges and limitations you need to keep in mind. These will help keep you grounded as you tackle your investigations.
Microbial contamination is inevitable and expected! People prepare sterile preparations, and we harbor microorganisms. We can’t eliminate people, so we need to mitigate risk through garbing, behavior, material movement, and cleaning. Even the engineering controls cannot prevent contamination.
The cleanroom suite is not sterile! EVER! Even after cleaning, under static conditions, there is chance microorganisms are present. Your goal is LOW contamination.
Compounders should review EM results frequently to ensure a state of control, but monitoring can neither prove nor disprove sterility. Viable sampling must not be used solely as a release test for compounded sterile preparations.
Viable sampling cannot and need not identify and quantify all microorganisms in the sterile compounding area. It is semiquantitative. This significant limitation exists because of the growth-based methods used in sample collection. We will only recover the microorganisms that like the media, incubation time, and incubation temperatures we provide. However, we need to remember that viable sampling is a spot check, a snapshot of what was happening during collection. If there are consistently exceeded levels, it indicates a loss of microbial control.
The sampling plan cannot prove absence of contamination, even when no growth was recovered. Microorganisms could still have been present during sampling. This won’t help you with excursion investigations, but it does reiterate that all zeros on your sampling report doesn’t mean you don’t have any microorganisms present. You just didn’t recover them. If you are getting consistent zeros during DYNAMIC operating conditions, it is going to be a red flag to inspectors. They will want to know why you haven’t recovered anything, as we expect to recover some growth during operations. Be sure you aren’t cleaning before sampling and that your media will support growth.
Remember, viable sampling is not perfect. It comes with its challenges and limitations but keeping these in mind will ensure you create and maintain a successful viable sampling program. Do you have questions about these challenges and limitations and how they might apply to your organization? Reach out!