Breaking the chain of infection

The clothing worn by healthcare staff plays an important role in breaking infection chains. The Hohenstein Institute has investigated the extent of the problem and ways of resolving it

To maintain the RAL-GZ 992/2 for Healthcare Linen, companies in the German Certification Association for Professional Textile Services must comply with particularly high hygiene and quality requirements
©Certification Association for Professional Textile Services

A study that examined the germ contamination of work clothing from 135 doctors and nursing staff in a hospital in Jerusalem found potentially infectious organisms in about 60% of the samples, including antibiotic-resistant bugs such as MRSA.1

In view of the role played by textiles as potential sources of infection in hospitals, the Hohenstein Institute in Bönnigheim, Germany, has developed a new type of germ transmission model which, in a first stage, tracks the transmission routes of micro-organisms in a public lavatory. Scientists observed to what extent there was a spread of bacteria, fungi or viruses from one germ source by the hands onto different objects in the room (e.g. lavatory brush, door handle, tap). It was then a question of determining to what extent these objects went on to become a source of infection.

The new germ transmission model was used to study, for example, how many micro-organisms were spread from the lavatory brush to the door handle by the hand of a person and what amount spread further by the hand of the next person opening the door.

The practice-orientated study conducted by the researchers is the first to correlate paths of germ transmission to currently known infectious doses of bacteria, fungi and viruses. Although, as expected, the number of viable germs decreased with each transmission step from hands to objects, some pathogens were still passed in infectious doses to other test persons through contact with contaminated surfaces.

Hohenstein Institute scientists are currently developing the germ transmission model further so that it can also be used for textiles in the healthcare system.

Scenarios of possible transmission of germs from one person to another via hands and different surfaces
©Hohenstein Institute

For the past few years, to improve infection prevention, surgical gowns and staff apparel have been antimicrobially treated The effectiveness of such products has been examined by specialists at the Hohenstein Institute with the help of standardised procedures based on practical applications. The results show that sometimes there are considerable differences in the effectiveness of antimicrobially active textile fibres.

In the procurement or rental of surgical gowns and staff apparel, it is therefore sensible to demand independent test certificates. These should prove the antimicrobial effectiveness of the textile raw materials in relation to pathogens such as MRSA, VRE, Salmonella, Staphylococcus aureus, Pseudomonas aeruginosa, Proteus spec. and Acinetobacter spec. This is the only way that indication-specific statements on the antibacterial effectiveness spectrum of staff apparel can be made.

However, bacteria are not the only cause of nosocomial infections: human-pathogenic fungi and virus infections, such as Norovirus, also play an important role. The examination of the effectiveness of antimicrobially active textile fibres in relation to fungi or viruses requires further test systems. The standard EN 14119 is based, for instance, on an agar diffusion test that is used for moulds, such as Aspergillus niger and Chaetomium globosum. Suspension tests according to DIN EN ISO 20743 or ISO 22196 can also be modified depending on the application.

The list of the test strains stated in the standards has been expanded at the Hohenstein Institute with additional germs, such as the yeast Candida albicans, Trychophyton mentagrophytes and the test virus MS2.

Within the framework of the AiF Research Project (AiF-No. 16039 BG) scientists from the Hohenstein Institute, in co-operation with the Thuringia Institute for Textile and Plastics Research (TITK) and the Saxony Textile Research Institute (STFI), have developed rental-suitable antimicrobial workwear based on cellulose regenerated fibres and then classified these in relation to their processing and characteristics of use.

The objective of the research project was to combine features such as protective function, high mechanical durability, long service life and ease of washing as well as a good thermal/physiological function (comfort) into one piece of clothing and then to produce a pure white, antimicrobial, rental-suitable and comfortable piece of workwear from cellulose regenerated fibres. Cellulose regenerated fibres have similar characteristics to cotton, which is preferred by many wearers due to its high level of comfort. Cellulose fibres can also be antimicrobially treated easily and permanently.

The Hohenstein research project, if successful, will in future facilitate permanent prevention against germ growth through the use of antibacterially effective ceramic coatings for continuous batch washers.
©Hohenstein Institute

Often the antimicrobially effective work-wear on the market ascribes its effectiveness to silver, which is embodied in the fibres. But silver, depending on the form in which it is applied onto or into the fibres, manifests discolouring or darkening effects during washing or under other external influences. Pure white workwear is preferred due to its association with cleanliness in hygienically sensitive areas.

In the development of new materials, initially three fibre variants were produced to which zinc, zinc oxide and silver nitrate were added. Zinc, which to date has hardly been used in textiles, is characterised as an active substance with the same benefits as silver: it is harmless to health, is a well-researched agent, and in contrast to silver, is not expected to discolour during processing and washing.

The results show that the new zinc-doped fibre variants can be used for producing workwear with a high proportion of cellulose fibres. Although titanium oxide was added to the silver nitrate variant to avoid the subsequent discoloration of the yarn in the manufacturing process, it did not lead to any improvement. Although the colorations were brighter, they continued to exist.

The quality of the new fibre variants was examined in a practical application. The textile technical minimum requirements such as size details, wear comfort and rental suitability were tested using the specifications from DIN 10524 as well as the antimicrobial effectiveness after up to 100 washing and drying cycles.

The positive results confirm that in the research project, the groundwork for a new and innovative approach for antimicrobial textiles through the use of zinc and cellulose regeneration fibres was laid. These newly developed fibres and the ensuing fabrics generated effective hygiene protection, pleasant wear comfort and a high rental suitability and can also lead to improved hygiene and to a decline in infectious diseases transmitted primarily through food.

Proper processing and storage is the second important component for textile hygiene in healthcare systems. Laundries that have the RAL Quality Certification Mark 992/2 for the proper care of hospital linen, demonstrably cover all the requisite hygiene measures for infection prevention. This applies both in relation to the building, such as the separation into a ‘contaminated’ and ‘clean’ area and also to the necessary quality management with its specifications for general hygiene through to the disinfecting washing procedures to be used.

The RAL Quality Certification Mark 992/2 for the proper care and processing of hospital linen is awarded only to companies who continually and fully comply with these specifications and who have been tested by an independent institute. The testing system of the RAL Quality Certification Mark 992/2 has developed over decades as a result of the practical collaboration of medical facilities and laundries.

When it comes to processing workwear, dental practices face particular problems

When it comes to processing workwear, dental practices face particular problems because the small amounts of laundry make it difficult for them to find a commercial laundry operation with monitored washing procedures. While gloves and masks are disposed of after every patient, clothing is not washed until the end of the day in many practices, and then only in a normal household washing machine. Experts at the Hohenstein Institute have studied in depth what types of germs are lurking on tunics after a day’s work and how these can be reliably returned to a hygienically sound condition.

Pathogens can be transferred from the patient to the clothing of the practice\'s employees through the air, particularly during drilling and rinsing. The transmission risk is especially high here as these items are not changed after every patient, unlike gloves and masks
©Kzenon - Fotolia.com

Among the germs feared by dentists are viruses, particularly HIV, hepatitis B and C and herpes, as well as bacteria such as tuberculosis pathogens or staphylococci. Fungi are often underestimated, even though they are a much more common problem: more than 70% of all people wearing dentures carry the oral thrush organism Candida albicans. These pathogens can spread to the employees' clothing through small drops transferred during dental treatments, for example when drilling or rinsing.

A study by the Hohenstein Institute examined the hygienic performance of different household washing procedures using special germ carrying cloths – so-called bioindicators. The results showed that yeast fungi such as Candida albicans as well as most bacteria can be destroyed by low temperature cycles. Skin fungi, viruses and more resistant bacteria can usually only be removed at washing temperatures of at least 60°C using an all-purpose washing powder with bleaching agent or hygiene additive.

From a hygiene point of view there are no objections to washing dental practice work clothes in a household machine, as long as water temperatures of at least 60°C are reached and suitable washing additives are used in sufficient quantities. The efficiency of the washing procedure should be checked at regular intervals, particularly with older machines, to avoid the risk of recontamination of the washed items caused by pathogen residue in the machine.

Washing machine performance can be verified using the Hohenstein Institute bioindicator cloths, which are loaded with bacteria, viruses or fungi and are added to the laundry at regular intervals. The Hohenstein microbiological laboratory subsequently determines whether the test pathogens were reliably destroyed.

Until now the use of chemical/thermal washing procedures has been the most important hygiene measure in commercial or hospital laundries and these have helped reduce germs in textiles effectively. In practice, however, the moist, warm ambient conditions in commercial laundries are ideal for germ growth and often recontamination of already disinfected and washed textiles can occur. Within the framework of an AiF Research Project (AiF-No 16102 N), in co-operation with the Friedrich Bauer Institute, Bayreuth, a ceramic coating developed for continuous batch washers should help to prevent this in future. Its permanent antibacterial effective-ness is due to copper and silver particles incorporated into the ceramic material.

Investigations have shown that a new contamination of the linen can occur during rinsing immediately after the disinfection process

Investigations have shown that a new contamination of the linen can occur during rinsing immediately after the disinfection process. Such recontamination with micro-organisms impairs the microbiological quality of the entire process since there is no further disinfection of the linen in the subsequent steps. The cause of the recontamination is primarily to be found in the extraction presses, presses and centrifuges. Biofilms form here as a result of contamination of the rinsing water or through independent bacteria, since the hygrothermic moisture and temperature conditions in these areas are ideal for bacteria to settle.

These biofilms are a constant potential culture medium and not infrequently are a considerable problem for maintaining the hygiene status. The objective of the Hohenstein researchers was the development of an effective and permanent antibiofilm-coating that covers both the interior walls and the perforated exterior walls of the washing drum of the continuous batch washer.

The first step of the project investigated how many effective substances had to be used to achieve the desired antibacterial effectiveness of the coating. Different coating modifications were tested in comprehensive microbiological investigations. As well as standardised test procedures for the investigation of antibacterially effective surfaces, new test systems developed within this project were also used.

A combination of biocide metal ions of silver and copper showed the strongest effectiveness rates in a two to three-layer coating. Not only could the bacteria be totally suppressed, but the coatings also showed a significantly better removal of the so-called biofilm plaques, compared with uncoated metal.

Scientific material data for an optimised coating combining silver and copper ions was established, and it was determined that the metal ions were only very slowly washed out in the various detergent solutions. Projections of the measured release rates state a permanent effectiveness of the coating over a period of 10–15 years. The adhesion of the coating was also investigated, and was found to show good resistance to mechanical influences.

The results achieved in laboratory conditions were verified in near real life conditions. These results also confirm that a combination of biocide metal ions of silver and copper are the most effective.

Reference

1. Wiener-Well et al., Am J Infect Control, 2011

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