How to evaluate if microorganisms isolated from sterile drug production environments monitoring are undesirable

: This study addresses the identification of undesirable microorganisms (MOs) recovered during the environmental monitoring in manufacture of sterile medicinal products. We developed a methodology evaluation based on a decision tree; then, such approach was applied to hypothetical scenarios of uncommon MOs isolation in sterile drugs production settings. The scenarios were formulated on the basis of our field experience, in terms of both MOs selection and types of sampling site. The MOs were chosen in order to include emerging pathogens and MOs responsible for drug recall, and several sampling sites were considered for their detection (air, surfaces, and personnel). The classification of the unusual MOs revealed that most of them were undesirable, because they represented the loss of environmental control or a potential impact on the quality of the product. In some cases, the uncommon MOs were not considered as undesirable. Therefore, our results demonstrated the importance of a methodology, also in terms of recovery rate of unusual MOs and of the threshold probability for the unacceptability (e.g., 1% or 5%). The proposed methodology allowed an easy and documented evaluation for the undesirable MOs isolated from the environment of the analyzed settings for sterile drugs production.