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Necessity of cleanroom socks for cleanroom entry

By Tim Sandle - PhD

Introduction

Most of the microbial contamination within the pharmaceutical facility can be traced to humans working in cleanrooms. Therefore, risk-based thinking necessitates taking steps to reduce the likelihood of personnel derived contamination and one such measure includes improving and expanding the range of cleanroom clothing. Improvements to the design and degree of coverage provided by cleanroom clothing has developed through an iterative process, with aseptic areas gravitating towards the complete coverage of skin (and with the final piece of the human jigsaw being the introduction of goggles). The contamination control intention is to cover all facial skin and prevent the shedding of droplets and particles.

With the new version of EU GMP Annex 1 (issued in August 2022) a new clothing element was introduced – the requirement to wear cleanroom socks prior to entry into Grade C and Grade B cleanrooms (this is something achieved by undertaking a pre-change, to remove outdoor clothing, in a controlled-not-classified area). This requirement appears on page 20, under section 7.14:

“Outdoor clothing including socks (other than personal underwear) should not be brought into changing rooms leading directly to grade B and C areas. Single or two-piece facility trouser suits, covering the full length of the arms and the legs, and facility socks covering the feet, should be worn before entry to change rooms for grades B and C. Facility suits and socks should not present a risk of contamination to the gowning area or processes.”

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With this requirement, personnel need to change from outdoor clothing into suitable tunics, including changing their socks (and shoes) under controlled-not-classified (CNC) conditions, prior to presenting themselves to a Grade C or Grade B changing room. This fits with one of the fundamentals with a facility contamination control strategy: personnel are the primary source of contamination in cleanrooms(2) and the process of minimising contamination begins by reducing the level of contamination presented to changing rooms through special clothing that reduces the particulate emission rate(3). Reducing the microbial load in changing rooms reduces the levels presented to the cleanroom suite.

The reasoning behind the inclusion of cleanroom socks is to address issue of microbial contamination both on feet and on the external surfaces of personal socks, together with the release of oils and perspiration, and the additional risks arising from foot health. These various factors are examined.

Contamination from feet

Each person possess slightly different skin microbiome, and this is the product of intrinsic and environmental factors that affect the diversity and quantity of microorganisms (including skin thickness, anatomical features, distribution of sweat glands, pH, and the availability of oxygen). This makes the microbial topography of human feet sometimes unpredictable and subject to change. Despite the variations, there are some common genera that inhabit the foot (as advanced by the research underpinning the Human Microbiome Project), including bacteria: Corynebacteriaceae, Micrococcaceae, Propionibacteriaceae, Actinobacteria, Clostridiales, Lactobacillaceae, Streptococcaceae, Enterobacteriaceae, Moravellaceae, Neisseriaceae, Pastereullaceae, and Proteobacteria; and fungi: Malassezzia, Cryptococcus, Aspergillus, Rhodotorula, Epicoccum, Saccharomyces, Candida, Epidermophyton Microsporum, and Trichophyton(4). There is a relationship between many of these genera and the organisms commonly isolated within cleanrooms(5).

The diversity relates to the foot having two different ecologies in regions that are moist (the toe interdigital web space) and dry (the heel). The average number of bacteria colonising the feet ranges from 103 CFU/cm2 on the dorsal surface to 107 CFU/cm2 in the fourth toe cleft. Numbers of fungi are highest on the heel, averaging reaches 80 organisms(6). The presence of these organisms is high when feet are exposed or socks are touched as the microbial population found on the feet is relatively unstable. This variety of organisms demonstrates the range of organism that can be deposited onto everyday socks (and which also present a more direct risk from any personnel who arrive at work not wearing any socks). For this reason, wearing cleanroom socks that are of a suitable size and which are suitably thin and which can be pulled over outdoor socks is recommended. This way each person can avoid depositing organisms to the level that would occur should personal socks be removed. Putting cleanroom socks over outdoor socks also creates lower levels of contamination on operator hands, making the hands easier to sanitise.

Foot Health

For some people, the risks of microbial contamination are elevated due to the health of the feet. This will later the microbial numbers and types. Microbial foot disorders are relatively common especially among those who do not take foot hygiene seriously. Poor foot health can relate to poor cleanliness overall, diabetes mellitus, ulcers, fungal infections and so on(14-16). For example, foot ulcers(17), as with other wounds to the foot(18), lead to a greater abundance of Gram-negative bacteria. Metagenomics relevels the core microbiome to be an abundance of Alcaligenes, Pseudomonas, and Burkholderia (organisms that are relatively harder to kill with cleanroom disinfectants compared with Gram-positive bacteria). In addition, those with forms of foot dermatitis will release more particles(19), and the ability of standard socks to retain particles will be relatively limited.

Sock selection

For entry into cleanrooms, clothing should be of a low particle generation and the same principle applies to cleanroom socks. Other considerations for cleanroom socks include the need for operator comfort during regular and extended wear, which will relate to the materials used and the level of friction resistance. For socks that are relaundered, the material quality should not diminish with laundering across a pre-set number of wash cycles. Furthermore, some facilities require socks to be decontaminated, which means that the material must be suitable for sterilisation without being subject to additional damage.
Socks can also degrade due to oils and sweat released from the feet(20). The degree of perspiration will be a factor of individuals, the surrounding environment, and the period of time that the sock is worn for. These factors should have been assessed by the vendor, such as the use of quick-dry materials which absorb a greater quantity of sweat.

Contamination from socks

As indicated above, everyday socks will carry a level of microbial contamination. Microbial levels will be  exacerbated by infrequent changing and from elevated levels of physical activity, where socks as remain moist due to sweat and dirt for a prolonged period. Socks function as incubators for microorganisms due to the moisture content and a pair of feet contains some 250,000 sweat glands which typically produce over 280mL of perspiration per day (and people with hyperhidrosis will produce even larger quantities)(7). For people with pre-existing fungal infections, the sock provides an ideal climate for reinfection as many fungi can utilise the organic material within a sock(8).

In addition, socks can pick up a diversity of microorganisms from the household environment and pets, where microorganisms will attach to the fibres of the sock through surface adhesion (this interplay with the environment is influenced by different climates and geographies)(9). For pet owners, especially those with dogs, there are many cases of microbiota similarity between human and animal, across various body parts including socks and feet(10) plus the likelihood of socks carrying pet hairs(11). When socks are not changed in CNC areas, it is highly likely that these microorganisms will be deposited into the changing room. In addition, when illness or infection occurs, the types of proportions of organisms will alter, altering the balance of what might be deposited onto the sock surface. Moreover, the ability to transfer microorganisms from person to surface and from person to person has been shown in numerous studies, across many decades, relating to pathogen cross-infection in communal changing areas(12, 13).

Does the switch to cleanroom socks work?

While the change into cleanroom socks prior to entry into changing rooms meets risk based criteria for contamination control (a probable risk based on high severity and likelihood sees the severity reduced and the likelihood substantially lowered, data from the pharmaceutical sector is limited. However, a study relating to a pharmaceutical facility in south-east England, in relation to gowning qualification where settle plates are exposed, saw a 30% reduction in contamination following the introduction of cleanroom socks prior to entry to a Grade B cleanroom (as evaluated over a one year period). As well as the reduction in numbers, there was a fall in foot-associated Gram-negative bacteria, notably Acinetobacter spp.

Summary

A suitable technical clothing system reduces the contamination released by humans and this paper has considered an important aspect of cleanroom clothing control - the introduction of cleanroom socks. The requirement for personnel to change their socks is a new recommendation made by European Regulators and it will become a requirement as a pre-change prior to entering Grade C and Grade B cleanrooms. Based on the microbial levels associated with feet and sock, and the likelihood of cross contamination, the switch to putting cleanroom socks prior to entry to a classified changing room provides a useful addition to a facility contamination control strategy.

References
  1. EU GMP Annex (2022) on manufacturing of sterile medicinal products, of Eudralex volume 4 :  https://health.ec.europa.eu/system/files/2022-08/20220825_gmp-an1_en_0.pdf
  2. Hyde, W. (1998). Origin of bacteria in the clean room and their growth requirements. PDA J Sci Technol; 52:154–164
  3. Romano, F., Milani, S., Joppolo, C. (2020) Airborne particle and microbiological human emission rate investigation for cleanroom clothing combinations, Building and Environment, 180 https://doi.org/10.1016/j.buildenv.2020.106967
  4. Adamczyk K., Garncarczyk, A., Antończak, P. (2020) The foot microbiome, Journal of Cosmetic Dermatology, 19 (5): 1039-1043
  5. Sandle, T. (2011). A Review of Cleanroom Microflora: Types, Trends, and Patterns, PDA Journal of Pharmaceutical Science and Technology, 65 (4): 392-403
  6. Skowron, K., Bauza-Kaszewska, J. Kraszewska, Z. et al. (2021) Human Skin Microbiome: Impact of Intrinsic and Extrinsic Factors on Skin Microbiota. Microorganisms 9, 543. https://doi.org/10.3390/microorganisms9030543
  7. Ahmed ME, Le Quesne PM (1986) Quantitative sweat test in diabetics with neuropathic foot lesions. Journal of Neurology, Neurosurgery & Psychiatry:1059-1062
  8. Stacey, A., Atkins, B. (2000) Infectious Diseases in Rugby Players, Sports Medicine, 29: 211-220
  9. Callewaert, C., Ravard Helffer, K., Lebaron, P. (2020) Skin Microbiome and its Interplay with the Environment. Am J Clin Dermatol 21, 4–11
  10. Coelho, L.P., Kultima, J.R., Costea, P.I. et al. (2018) Similarity of the dog and human gut microbiomes in gene content and response to diet. Microbiome 6, 72 https://doi.org/10.1186/s40168-018-0450-3
  11. Helen Louden, H. (2015) Walking on broken glass : wound care, Home Medical Chronicle 2015 (3): https://hdl.handle.net/10520/EJC167694
  12. Rebell, G. C.; and Camp, E. (1947) Dermatophytosis at an Infantry Post. Invest. Dermat. 8: 291-316
  13. MacFarlane, B., Falkland, M. (2020) Treatment of inflamed fungal skin infections The Australian Journal of Pharmacy, 101 (1201): 85-88
  14. Thomas J, Jacobson, G., Narkowicz, C. et al (2010) Toenail onychomycosis: an important global disease burden. J Clin Pharm Ther, 35: 497-519
  15. Ghannoum MA, Hajjeh, R., Scher, R., et al (2000) A large-scale North American study of fungal isolates from nails: the frequency of onychomycosis, fungal distribution, and antifungal susceptibility patterns. J Am Acad Dermatol, 43: 641-648
  16. Rastogi A, Sukumar, S., Hajela, A. et al (2017) The microbiology of diabetic foot infections in patients recently treated with antibiotic therapy: A prospective study from India. Journal of Diabetes and its Complications, 31: 407-412
  17. Jnana, A., Muthuraman, V., Varghese, V. Microbial Community Distribution and Core Microbiome in Successive Wound Grades of Individuals with Diabetic Foot Ulcers, Applied and Environmental Microbiology, 86 (6): https://doi.org/10.1128/AEM.02608-19
  18. Bowler PG, Duerden BI, Armstrong DG. (2001) Wound microbiology and associated approaches to wound management. Clin Microbiol Rev 14: 244–269
  19. Rani Z, Hussain, I. and Haroon, T. (2003) Common allergens in shoe dermatitis: Our experience in Lahore, Pakistan. Int J Dermatol, 42: 605-607
  20. Cleary, G. (1984) Transdermal Controlled Release Systems, In Langer, R. and Wise, D. (Eds.) Medical Applications of Controlled Release, Vol. 1, CRC Press, USA, pp203-252