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Updated: Feb 29

Response to Editorial | Open Access | Published 26th July 2023

Response to Editorial by Tim Eaton - The Fallacy of Sterile Gowns (Russell Madsen)

Author : Tim Eaton

Dear Sir....

I read with interest the guest editorial item, ‘The Fallacy of Sterile Gowns’, that was published in Volume 28, Issue 1 of the EJPPS. The item suggested that commercially laundered, non-sterilised gowns for use in pharmaceutical aseptic processing areas (APAs), have been shown to contain few, if any, microorganisms prior to gowning. Furthermore, it was stated that the use of such gowns would not jeopardize product quality but would reduce costs and save energy. This is generally accepted by those with knowledge of aseptic processing activities and an understanding of cleanroom gowns and the associated gowning process. To support these claims, it is useful to utilise microbial data that relates to the actual concentrations on gowns following laundering but prior to sterilisation, the concentrations following gowning and also after their use in APAs.

To provide gowns of the appropriate cleanliness levels, specified decontamination (washing, drying, packaging) cycles are used. For a well-controlled laundry facility where this is undertaken, the gowns are washed using purified water and following washing, the drying and packaging activities are completed within a cleanroom of appropriate cleanliness levels, where the laundry personnel are required to also utilise similar gowns and complementary protective attire. With these levels of control, the resultant bioburden on the processed gowns is expected to be low and this is confirmed by testing (stomaching, filtering, incubation and enumeration) to be on average, approximately 25 CFU. For a one-piece gown, that is typically worn within an APA, the total (internal and external) fabric area is approximately 4 x 104 cm² and this presents an average gown surface microbial concentration of 6.25 x 10-4 CFU/cm². This is a very low surface concentration and for higher risk APA activities, gowns are typically subsequently sterilised using processes (normally radiation or wet heat) that ensure there is effectively no residual viable microbial contamination prior to use.

During the gowning process, personnel are required to put on the gown using procedures that minimise their contact with the external gown surfaces to control the transfer of personnel borne microbe-carrying particles (MCPs). However, it has been shown that personnel, on average, disperse around 1940 MCPs per minute 1 and so it is inevitable that a significant number of these airborne MCPs will be deposited onto the surface of the gown during gowning. As part of the evaluation of the effectiveness of the gowning procedure to control the number of MCPs transferred to the external surfaces of the gowns (by both surface contact and airborne deposition - often referred to as gowning qualification), selected locations of the full protective attire, including the gown, are sampled and the number of recovered MCPs determined. A review of such data (12 months) for a well-controlled gowning operation utilising sterilised gowns, a total of 82 CFU was recovered from 1466 (55 mm diameter) contact plates. With a plate area of 24 cm², this is a surface concentration of 2.3 x 10-3 CFU/cm² which is approximately 3.7 times greater than the residual concentration following the gown decontamination process and when taking into account the recovery efficiency associated with contact plates (approximately 50%) compared to the high recovery gown bioburden testing method, the increase is likely to be at least twice this value. However, it can be determined that if the gown was non-sterilised, at least 79% of the gown surface microbial contamination would result from the gowning. For interest and completeness, for the same period, similar analysis from the surface of gowns that have been utilised for manufacturing activities in the APA and sampled on exit, indicates a similar concentration of 1.37 x 10-3 CFU/cm².

To understand the influence on product quality resulting from the use of non-sterilised gowns, it is useful to consider the maximum action limits for surface viable contamination included in Annex 1 of the EU GGMP 2. These values are 5 CFU and 25 CFU per (55 mm diameter, 24 cm²) contact plate with associated concentrations of 0.21 CFU/cm² and 1.04 CFU/cm² for Grade B and C environments respectively. When compared with the pre-sterilisation gown bioburden concentrations, these concentrations are 336 and 1664 times greater than specified for Grade B and Grade C environments respectively and indicate minimal risk to product quality.

Consequently, this information does support the claim that such non-sterilised gowns would be unlikely to jeopardize product quality and could reduce costs and energy. However, the laundry facility contamination control measures are a key consideration to ensure that the post decontamination cycle gown surface microbial concentrations are adequately controlled, and the nature of the activities and risks within the associated cleanrooms also need to be understood.



01. Eaton T, Whyte W. Effective Re-usable Cleanroom Garments and Evaluation of Garment Life European Journal of Parenteral and Pharmaceutical Sciences 25 (4), 2021.


02. European Commission Guide to Good Manufacturing Practice, Annex 1:2022. European Commission, Enterprise Directorate-General, Brussels.



Tim Eaton

Steriles Manufacturing Specialist

AstraZeneca Operations

Macclesfield, UK


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