Air Sampling – How to do it the Right Way

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Air sampling is a critical function of any Quality Control (QC) laboratory associated with a Pharmaceutical, Biotech, or healthcare facility, yet many QC personnel are unaware of the best methods of microbial air sampling for their particular needs. There are several mechanisms for sampling viable particulates out of the air, and different mechanisms benefit different testing requirements. One must first determine the type of sampling device and scheme, which fits their specific needs, then work with the available technologies that best suits them to meet their testing requirements.

If one is unclear on how to most effectively use a microbial air sampler or compressed gas monitoring system to ensure the safety and health of your employees and customers, it’s important to understand the types of microbial air sampling devices and their individual benefits.

Passive vs. Active
There are two primary methods for microbial air sampling: Active and Passive monitoring. In active monitoring, a microbial air sampler is used to force air into, or onto its collection medium (e.g., Petri Dish with nutrient agar based test media) over a specified period of time. The collected culture can then be incubated and analyzed (ie., count bacterial and/or fungal, colony forming units (CFU), and identify if required). In passive monitoring, settle plates (Petri dishes) are opened and exposed to the air for specified periods of time to determine what microbiological particles may be present in the environment, as they may settle out of the ambient air, and onto the media surface of the Petri Dish.. These plates are then incubated and analyzed.

Both passive and active monitoring have their own strengths and weaknesses. Passive monitoring is not aggressive and may miss critical microbes, but offers a lengthy (4-hour) sampling period, and a very low cost associated with it. Active monitoring requires equipment purchases, additional training, device qualification, and most devices offer a shorter sampling period (e.g., 10-minutes), which can be both a benefit, or a burden. But, active monitoring devices are more ideal for situations with low microbial concentration, which includes most clean rooms, since microbial contaminants will be less likely detected by passive monitoring.

With both Passive and Active monitoring, personel are required to physically start the process, set up the settling plate, or device, and remember to check samples in process, label, and submit the test plates for incubation and analysis. With the analysis, active monitoring will allow for both a quantitative and qualitative analyses of the sample, by allow the determination of contamination levels per volume of air sample, while with passive monitoring one can only obtain a qualitative analysis.
Because there is no standardized protocol for collecting air samples, it is difficult to determine whether one method is “better” than the other. However, knowing the difference can help you determine which solution will work best in your work environment. It is also important to note that microbial air samplers will turn up different results within the same area, or room based on the time and activity of the room. As such, both “Dynamic” and “Static” condition monitoring data should be collected in an area, or room. If a sample is taken during a surgery, for example, it will likely show more microbial elements than air sampling done in the same room with fewer factors, such as personnel and equipment, contributing to the microbial population.

When it comes to air sampling, the best method is one that works best for you and suits your specific needs while keeping your employees and clients safe.