Plate-Counting Techniques for Average Bioburden Below the Limit of Detection

Current methods for estimating average bioburden on medical device products, following ISO 11737-1:2018 with low bioburden or high limit of detection, present challenges for bioburden-based sterilization methods (e.g., radiation sterilization by ISO 11137-2:2013 or ISO 13004:2022). The inability to accurately estimate low bioburden counts per device can result in an overestimation of device bioburden and an artificially decreased challenge during validation. It can also force products to be sterilized at higher doses if the overestimation of bioburden prevents use of a lower dose than would otherwise be possible. This article describes a plate-counting technique for producing consistent and accurate estimates of low numbers of bioburden for products, even when tested as a sample item portion or with a high dilution factor relative to the average bioburden count.