Overkilling Uncertainty, New TIR Seeks Clarity for Interpreting Bioburden Data
When companies are testing a medical device’s bioburden — a measure of how much and what types of viable organisms are in or on it after manufacturing — they might question how exact their results should be or what to do if the numbers seem off.
by Anna Medaris, AAMI Array Magazine | October 12, 2023
Sopheak Srun, Principal Sterilization Scientist at Cretex Medical | QTS, was featured in an AAMI News in Conversation interview.
When companies are testing a medical device’s bioburden—a measure of how much and what types of viable organisms are in or on it after manufacturing—they might question how exact their results should be or what to do if the numbers seem off.
However, the current international standard related to the topic, ISO 11737-1, Sterilization of health care products — Microbiological methods — Part 1: Determination of a population of microorganisms on products, remains a fairly high-level document to account for its broad scope. To touch on more granular topics and issues, device manufacturers currently rely on their best judgement and shared best practices.
That’s why members of AAMI Microbiological Methods working group under the Sterilization Standards Committee (ST-WG08) are developing a new technical information report (TIR), AAMI TIR106: Microbiological methods — Understanding and use of product bioburden data, which curates this disparate scientific and industry knowledge. Their goal is to provide clarity for medical device manufacturers with user and patient safety in mind.
“A lot of companies would have issues with just knowing how to interpret [bioburden] data, or they run into issues with notified bodies or regulators in having some of these conversations about their data,” Sopheak Srun, co-chair of ST-WG08, told AAMI Digital Staff Editor Brian Stallard during a recent AAMI News in Conversation interview.
Sometimes, Srun added, these conversations can get “contentious.” The new document, which is intended to be used in conjunction with international standards, is designed create consistency across the industry, he said.
Srun’s co-chair and convenor for International Organization for Standardization (ISO) technical committee 198/WG08 (Microbiological methods), Amy Karren, of W.L. Gore and Associates, also joined the conversation. She first explained that the new TIR specifically addresses the natural bioburden, or what’s contributed to a device during the manufacturing process.
“Even in clean rooms, when you make a device, it has viable microorganisms on them,” she said. “We try to control the number and the types, but we still need to know what they are, and that's why we do bioburden testing.”
One key element of the document, Karren said, is its differentiation of the criticality of bioburden data among sterilization modalities.
“Some sterilization methods are bioburden-based and so bioburden is incredibly critical—you need to have it as accurate and estimated as best you can,” she said. But in other situations, like with overkill sterilization methods (e.g., moist heat), “bioburden is really for monitoring—you need to know what it is and that it's a consistent and a controlled level.”
Another part of the new report addresses what to do when a bioburden count seems suspiciously high.
“When that happens, you have to investigate it. You have to look at: Is this a true result? Did the lab screw up? Was there something wrong in the manufacturing process? Was a critical process skipped if – let's say your manufacturing process involves cleaning – did they forget to clean it right? Or it could even be: Was there a change in the process that caused the bioburden to become higher?” Srun asked. “It could be any number of things, and doing these investigations can be really difficult if you don't know where to start.”
According to Karren, AAMI TIR106 is intended to guide professionals on where to do just that.
“I’m very proud of this document. I think it's going to be great,” she said. “It is one of the few documents that has a lot of guidance also for labs on data interpretation. For instance, if they're not in an accountable range, what do you do for an estimate? Those kinds of things.”
Karren said the soon-to-be published new TIR was developed by a working group whose membership includes bioburden experts from both labs and industry, and has seen many iterations on its way to becoming a comprehensive document.
But what if ISO 11737-1 were to change? The soon-to-publish TIR is intended to stand on its own, even if and when the international standard is revised, Karren added. “The intent of the TIR was more to understand the output of that standard,” she said. “And so what we were hoping is that the TIR can influence that the output is clearer in the standard.”
