Tracking the source of contamination in an isolator: contribution of chemical indicators and swab sampling

Background
Microbiological monitoring of isolators [1], [2] has been performed for more than 5 years at our hospital center. Among the 2,190 samples collected in 2025, the positivity rate was 0.9% for sterile gloves, 3.3% for neoprene gloves, 1% for passive air monitoring by settle plates, and 0% for surfaces. In addition, an in-depth analysis showed higher contamination rates for gloves located near the transfer hatch: 1.4% versus 0.5% for sterile gloves and 3.8% versus 2.8% for neoprene gloves.

Objectives
To investigate one possible source of contamination by assessing the homogeneous distribution of the sterilizing agent within one isolator and to verify the absence of contamination on incoming materials.

Materials and Methods
Over a period of slightly more than one month, at a rate of two tests per week and in collaboration with all pharmacy compounding technicians, including the hygiene referent, chemical indicators corresponding to the sterilizing agent used were introduced into baskets during several decontamination cycles. At the end of each cycle, swab samples were collected [3] exclusively from connectors, syringes, and vial stoppers after sterilization in order to ensure reproducibility and allow comparison of results.

Results
During these 5 weeks, among the 10 decontamination cycles evaluated, all 60 chemical indicators reacted uniformly upon exposure to the sterilizing agent, demonstrating homogeneous diffusion within the baskets regardless of load organization and composition. Furthermore, all 60 microbiological swab samples collected from incoming materials were negative. However, one routine microbiological sample taken from a sterile glove on the same day as one of the test sessions was positive.

Discussion / Conclusion
Based on the study results, the source of contamination does not appear to originate from incoming materials. However, since microbiological qualification is performed only once per year, the use of chemical indicators combined with swab sampling provides additional monitoring. The method is simple and reproducible. Following the study, good practices for sterile glove donning were reiterated, including the requirement to change gloves every three preparations and/or every 30 minutes, as well as after each exit from the preparation area. Consequently, other potential causes should also be investigated, such as the rotation of cleaning/disinfection agents and the type of undergloves used.

Keywords: pharmaceutical preparations; risk management; equipment contamination

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