Deciphering Requirements for Environmental Testing

Manufacturers should keep bioburden in mind at all times and use ISO 14644 and ISO 14698 to help satisfy environmental monitoring and testing requirements.

Scott Mackin

A technician at Microtest performs bioburden testing using the aseptic technique. There are no commonly accepted levels of environmental bioburden.
Industrial sterilization and contamination control programs are critical to medical device manufacturing. This article reviews the key elements of a best-practice environmental testing program, including sterilization standards and the critical factors in maintaining controlled environments.

The Challenges of Environmental Requirements

One of the biggest challenges facing medical device manufacturers in designing, implementing, and maintaining their sterilization and environmental monitoring programs is determining what exactly is required for compliance.

For parenteral manufacturers, environmental control parameters are stringent. A collaborative effort between the FDA Office of Compliance in the Center for Drug Evaluation and Research, the Center for Biologics Evaluation and Research, and the Office of Regulatory Affairs produced a guidance, “Sterile Drug Products Produced by Aseptic Processing—Current Good Manufacturing Practice.”

By contrast, device manufacturers have to piece together a coherent and defensible strategy by choosing bits and pieces from different standards, guidance documents, and corporate policies. For small or inexperienced device manufacturers, the task is daunting, and they might only know the strength of their program after it has been reviewed or audited externally.

If and when environmental controls are implemented, companies often have little confidence in their practicality or that the programs will pass regulatory muster (i.e., an FDA audit). When employees do not buy into the value of the program, it often results in a system of documenting control failure rather than a program that demonstrates continued control and compliance. In most cases, this will negatively affect the entire environmental system, ultimately resulting in loss of production.

Large companies often have solid programs in place for commissioning new production areas, continued monitoring, and sterilization validation. Additionally, because many of these companies are experienced in satisfying a variety of regulatory requirements to market their products globally, their programs tend to be more comprehensive.

Particulate Characterization: Viable versus Nonviable

Ideally, data collection and analysis should correlate bioburden, product contamination, and sterilization efficacy.

Since the early days of Federal Standard 209 (FS 209), cleanliness classes have been assigned to clean zones using measured levels of nonviable particulates. Microbiologists and regulatory professionals initially struggled to draw a correlation between the levels of nonviable particles and viable particles present in the environment. They concluded that no direct relationship could be defined. However, because of the relative ease and practicality of continuous monitoring for nonviables, it remains the most reliable method for real-time assessment of environmental control.

With the exception of Class 100 (ISO Class 5) areas, there is a lot of ambiguity in determining what satisfies the microbial sampling requirements called out in many standards. There are no commonly accepted levels of environmental bioburden, especially in Class 10,000 (ISO Class 7) and Class 100,000 (ISO Class 8) areas. Because FS 209 expired and ISO 14644 has taken its place, ISO 14644 is recognized as the current standard for the design and validation of controlled environments.1 In addition, ISO 14698 provides manufacturers with concrete guidance in setting up the microbial portions of their programs.2 Still, it stops short of providing a definitive method for determining just how much microbial sampling is sufficient. Many manufacturers use the same calculation for their microbial sampling that is set forth in ISO 14644 to sample for nonviable particulates. Even so, there is no indication of what sample locations in the environment are most critical and which types of organisms (e.g., aerobic, anaerobic, fungal) must be recovered. Sampling requirements are open to interpretation, and written justification for a firm’s sampling procedures must be provided in its overall environmental monitoring plan.

Unfortunately, as sterilization validation programs rely more and more upon bioburden control and monitoring, these missing pieces become even more critical. If possible, manufacturers should evaluate methods of collecting and analyzing data that could correlate environmental bioburden, product contamination, and sterilization efficacy.

Sampling Plans

Regulatory agencies generally defer to a table or calculation for determining sampling frequencies and volumes. Often manufacturers must design an environmental sampling scheme by identifying critical areas of product contact or manufacturing activities. At first glance, oversampling sounds like an easy solution. But for many manufacturers, it is simply not a feasible approach with respect to budgetary or personnel resources. The expense associated with purchasing, validating, and maintaining sampling equipment, plus buying supplies and training personnel, is often prohibitive. In addition, many sampling schemes and control parameters are only verified quarterly or semiannually as set forth in ISO 14644, especially in Class 100,000 areas.3 For small and start-up medical device companies, it makes sense to outsource—that way they can draw on resources and expertise that might be too expensive to staff internally.

Validation: Controlling Costs and Understanding Requirements

Testing firms can help manufacturers develop a tailored monitoring program that is both fiscally reasonable and able to withstand external audits.

Before a cleanroom is commissioned, it’s necessary to plan for the collection of data required for validation, as well as the source of those data. Vendor responsibilities need to be clearly defined, managed, and documented in an agreement to avoid costly retesting. Having a clear understanding of the regulatory requirements and managing vendor activities effectively shortens project timelines, reduce expenses, and jumpstart production. ISO 14644 offers an overview of important performance parameters. It also provides guidance including requirements for start-up and qualification.4

Sterilization Method Selection

The method of selecting the most appropriate environmental monitoring and terminal sterilization programs should not only be a function of process method (e.g., gamma versus ethylene oxide); it should also take into account the level and nature of both the environmental and the product bioburden.

Device manufacturers have increasingly become aware of the importance of the relationship between their environmental monitoring and sterilization programs. This is especially true given the increased use of the VDmax method for sterilization validation. In fact,

Testing firms can help manufacturers establish training programs and protocol for working in a controlled environment.

ISO 11137, ISO 11737, ISO 13409, and AAMI TIR-33 all refer to the need to have an environmental monitoring program in place.

The VDmax method for gamma sterilization validation and control was developed by established manufacturers in the industry with numerous historical data regarding the normal ranges of environmental and product bioburden. It reduces costs associated with testing by reducing the number of samples required for sterility release (testing is damaging to product). The verification dose (release) test is performed at a high dose, decreasing the risk of failure at 25 kGy, a common dosing value.

It was easy for the experienced manufacturers to document their justification for using this method because they could review previous trends and had a good understanding of what could be considered a state of control. Such manufacturers already felt confident that the environmental programs they had in place were sufficient to support product bioburden control, reducing the potential of verification dosing failures. Now more and more start-up firms and component manufacturers are using the VDmax method for new product sterilization validations.

Bioburden Control

The use of the VDmax method reduces the amount of product required during quarterly dose audit testing, which in turn reduces the annual cost of product release testing. This makes the method especially attractive to start-up manufacturers. However, this method is not always the best option, especially for companies with limited experience with controlling bioburden. AAMI TIR-33 states that this method cannot be used when the estimated average bioburden exceeds the limit for the selected sterilization dose.5

Cost and product savings can quickly vanish during quarterly audits if there are high bioburdens. It is important to remember that the verification dose is performed at a sterility assurance level of 10–1, which indicates the probability of a microorganism being present on product after it has been sterilized. The dose is performed on a statistically smaller sample set.

An influx of unobserved resistant organisms can ultimately result in retests, if not revalidation—even in situations in which the bioburden count does not increase over historical levels. This makes understanding the nature of the typical bioburden as important as the levels themselves. Trending seasonal bioburden variations and identifying in-house isolates are two examples of how to gain this understanding.

Other Critical Factors

A number of other factors not always obvious to manufacturers are vital to an effective bioburden control program.

Raw Materials. Precautions should be taken to ensure that external bioburden does not travel into the production areas along with components and materials. Although specifications will vary, these materials should usually be removed from the original shipping containers and cleaned with a non-residue-forming disinfectant.

However, the level of disinfectant activity required is a function of the cleanliness class and its associated requirements. All materials should be stored for staging in controlled areas within or adjacent to manufacturing suites. In addition, every effort should be made to reduce or eliminate cardboard and paper products from the controlled environment. Process flow should be clearly defined and qualified. Adhering to a plan helps manufacturers avoid surprises and deal with unknowns.

Personnel Training. There should be written and posted procedures for proper gowning and hand washing, and the basic microbiological principles involved in minimizing contamination should be understood by manufacturing personnel. Elements such as the location and placement of equipment and operators can significantly affect the risk of product contamination.

Some laboratories help manufacturers establish protocols for use in personnel training. Training documentation should be in place for all personnel who will work in the manufacturing area. For example, it is common to require workers to execute some type of gowning validation, using touch plates or swabs, before they are allowed to work in the controlled environment. An understanding of the types of clean garments that are appropriate for the specific activities and environment is important as well. This can affect cost and operator performance as well as environmental bioburden.

Housekeeping. There should also be written and posted housekeeping procedures and training documentation. Close attention should be paid to cleaning materials such as mop heads and disinfectants as well as the frequency of cleaning and documentation of cleaning activities. For example, a strong disinfectant can destroy the integrity of a nonporous surface. Mop heads and wipes must not shed or leave particulate. In addition, these cleaning materials must have use and rotation limits.


Unfortunately, there is not yet a single reference document for manufacturers to rely upon to design, validate, and demonstrate environmental testing compliance. ISO 14644 and ISO 14698 documents have eased the task significantly and are good resources for manufacturers of terminally sterilized products. The key is to keep bioburden in mind at all times. Step back and look at the manufacturing process, personnel, and environment as a whole when drafting a sterilization validation program.

The path to a solid understanding of bioburden starts with defining traffic patterns and identifying and limiting product and personnel contact areas. Characterizing, controlling, and understanding environmental bioburden levels and trends are the cornerstones of defining and implementing a solid environmental monitoring program that fully supports sterilization validation and release activities.

Scott Mackin is a project manager at Microtest Laboratories (Agawam , MA). He can be contacted at


1. ISO 14644, “Cleanrooms and Associated Controlled Environments—Part 1: Classification of Air Cleanliness” (Geneva: International Organization for Standardization, 1999).

2. ISO 14698, “Cleanrooms and Associated Controlled Environments—Part 1: Biocontamination Control—General Principles and Methods” (Geneva: International Organization for Standardization, 2003).

3. ISO 14644, “Cleanrooms and Associated Controlled Environments—Part 2: Specifications for Testing and Monitoring to Prove Continued Compliance with ISO 14644-1” (Geneva: International Organization for Standardization, 2000).

4. ISO 14644, “Cleanrooms and Associated Controlled Environments—Part 4: Design, Construction, and Start-Up” (Geneva: International Organization for Standardization, 2001).

5. AAMI TIR-33, “Sterilization of Health Care Products—Radiation—Substantiation of a Selected Sterilization Dose—Method VD” (Baltimore: Association for the Advancement of Medical Instrumentation, 2005).

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