Viable environmental monitoring provides critical information towards understanding the relative cleanliness of the sampled environment. Typically, viable airborne and surface data is collected to understand the total bioburden representative to a zone. Total colony forming units (CFU) recovered may be reviewed for trends and against action/alert levels to understand the relative control of bioburden in the sampled zone.
Development of an environmental monitoring sampling plan should be generated using any prescribed requirements (regulations, facility specific, etc.) along with a risk assessment specific to the zones to be sampled and their related processes. Considerations in development will be frequency of sampling, type(s) of sampling, airborne sampling volumes, media types utilized, incubation requirements, trending requirements, alert/action levels, and required responses to out of specification results.
Airborne viables are collected most often as active samples, with a pre-determined sample volume of air drawn onto a viable sampling plate. This data is typically reviewed in units of CFU/m3, with conversion from actual sampled volume to per cubic meter as required. Sampling a full cubic meter of air is generally not cost effective or time efficient, and smaller sampling volumes may be collected and converted. For example, with a sampling volume of 500L (0.5 m3), raw CFU results will be in CFU/500L and multiplied by two (2) to reach the normative unit of measurement CFU/m3. In considering the sampling volume for your environmental monitoring plan, TSS recommends reviewing the cleanliness level of the zone to be sampled. Generally, as the ISO class improves (the zone is cleaner), additional sampling volume should be collected to avoid conversion of low CFU results.
Surface viables are collected most often through direct contact of a media plate against a surface. Results are reported as raw CFUs and interpreted as CFU/plate.
Results from viable sampling should be reviewed often to determine trends and re-assess alert and action levels. Where samples trend much lower than associated criteria, it is typically recommended to lower the alert and action levels appropriately. Where they continuously exceed, review to determine if the alert/action levels are appropriate or too stringent. Any excursions from alert/action levels should be reviewed to determine the risk associated and a plan determined accordingly – which may include justification, acceptance, or action as required.
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