The past five years have seen a steady transition in control of decontamination and disinfection of healthcare garments, with most major laundries in this sector moving from feedforward control (using implied thermal disinfection) to feedback control (with quality assurance that disinfection is actually being achieved). The advantage of feedback control is that it permits the use of methods other than implied thermal disinfection, enabling all parties to lower their carbon footprint and meet climate change commitments while improving overall reliability of disinfection.

This has caused all parties to review their procedures for finding out what is going wrong when checks show that disinfection is failing and our Tip of the Month provides a useful chart detailing some of the possible reasons and what to do to address each of them.

These changes have gone ahead in parallel with much more prescriptive arrangements in some areas for domestic washing of healthcare uniforms, in order to achieve decontamination and disinfection by the staff who wear them. The advice given in this article is intended to dovetail with these arrangements, highlighting potential risks and how they might be addressed, based on best practice in the professional textile care sector.


Decontamination to achieve removal of soiling and staining

Most healthcare stains contain some protein (from, say, gravy or dairy residues) or vegetable matter (from foods containing starch, for example) and as such they provide nutrient for any micro-organisms including those with which they might come into contact in transit to the user or in the ward linen cupboard or staff locker. There is no point in concentrating solely on disinfection in the laundering process – all staining and soiling must be effectively removed. This calls for good washing disciplines and process monitoring.

Complete protein removal calls for correct control of pre-wash chemistry and temperature and pre-sluicing of heavily soiled work, to avoid partial setting of protein stains. It then demands accurate control of chemical dosing, mechanical action (with the correct load factor), time and temperature – the best processes effectively remove all traces of proteins but there are wide variations.

Many processes require an improvement in removal power for fatty oily or oily proteins using a low dosage of an appropriate emulsifier (with the correct HLB value) and this is particularly important for textiles containing polyester fibres (which have a strong attraction for oily proteins).

Essential process monitoring includes analysis of stained rewash (ideally by the chemicals supplier) and regular checks on the power of the process with respect to various soiling types using EMPA test strips.


Does disinfection equal sterilisation?

Sterilisation means reducing the concentration of micro-organisms to effectively zero, both on the surface of the textile and throughout its thickness. This is essential for garments and instruments to be used in the operating theatre, but it is neither practical nor even possible in laundering. Although not defined, disinfection is generally taken to mean reduction of viable micro-organisms on the textile surface to below 102 (100 micro-organisms per 10cm2), not zero, so disinfection certainly does not mean sterilisation.

At least one large healthcare system defines a requirement for chemical disinfection to be capable of reducing the contamination level by a factor of at least log 5, from say 107 to below 102. This is fine provided the laundry process also removes physically any local contamination where the concentration is higher than 107, but this is not usually a problem in practice.


Disinfection in the laundering process

Implied thermal disinfection has been used for many years and it has been widely verified that if the textiles pass through a wash stage which maintains 71C for at least three minutes plus mixing time, then all bacteria and viruses are killed with the exception of those bacteria which form spores (such as Bacillus cereus and Clostridium difficile (C.dif)). If the spore formers can be induced to open up and breed (by keeping the textiles in warm, moist conditions) then they go into the vegetative state and are also killed by implied thermal disinfection. However, few have managed to do this reliably, which is why these species can be so difficult to deal with. Bacillus cereus in particular tends to multiply in warm summer conditions, when outbreaks can become serious and the common solutions to date rely more on dilution than anything else. This has serious implications for processes which are designed for very low water flows in tunnel washers and may demand seasonal variations, especially when dealing with a sudden outbreak.

The widespread adoption of the European Norm (EN14065), which was revised and updated in 2016, has permitted the use of chemical disinfection, either instead of or combined with thermal. The use of sodium hypochlorite in a bleach rinse has been used effectively for many years on suitable textiles and works well, provided the concentration is maintained at 150ppm for at least three minutes plus mixing time. This is not easy because the strength of hypochlorite deteriorates in storage, calling for good controls. Quaternary amines (‘quats) have also been used and these have the advantage of being substantive: they cling to the surface of natural fibres, providing a degree of resistance to re-contamination after laundering.

Both of these are being superseded by the use of peracetic acid (PAA), which is a very powerful killer of bacteria in the vegetative state, provided it is used at the correct concentration for sufficient time. Hypochlorous acid is probably even more powerful (and might deal with some spore formers as well) but attempts to keep this sufficiently stable for practical use have not yet been successful.


Can disinfection be achieved in finishing?

In theory, one would expect finishing time/temperature combinations to achieve implied thermal disinfection and many have been surprised to find that this is not the case. One might think that drying and pressing a damp sheet for 25 seconds in contact with a metal ironer chest at 184C would give a high bug kill. Even more confidence might be placed in tunnel finishing polycotton garments for 22 minutes in a tunnel finisher with a continuous air-blast at 155C.

In practice neither achieves an adequate bug kill. The reason appears to be the ability of bacteria to survive in the moisture in the damp seams. This was demonstrated in one large contract for garments which were tunnel finished and which smelled sweet when they emerged, even though they were quite warm. However, within two days in the wearer’s locker they had acquired a stench.

The cause? Bacteria from contaminated rinse water were not being effectively dealt with, even under these apparently extreme conditions. These were breeding and multiplying in the locker and it was their excrement which caused the odour.


Assessing disinfection

Any reputable system for assuring disinfection to a required standard needs some form of monitoring to give justified assurance of the quality being achieved. There are three systems in common use, each of which has its attractions and the best systems use either two or all three in their EN14065 procedures.

a.            In-house monitoring in the laundry and sometimes in the healthcare establishment itself can employ dip-slides. A dip-slide is a sterile plastic strip with an area of 10cm2, which comes sealed in a sterile transparent plastic tube. Each side of the dip-slide is coated with a nutrient agar which permits growth of one species or groups of species. An operative can be trained in an hour or so to use and incubate the dip-slide to get a good estimate of whether disinfection is complete or whether bugs are surviving, either on textiles or on other surfaces.

b.            If verifiable certified records are required, the best techniques usually use sterile swabs which come in a sterile housing and which are wiped in a standard manner over the surface of the textile or machine surface to be assessed. The swabs are then replaced in their sterile tubes and sent for analysis to a certified micro-biological laboratory, who will issue a certificate detailing the level of contamination found. This analysis can be general (e.g. total viable count (TVC)) or specific (e.g. the level of C.dif found).

c.            Pre-infected textile swatches (processed once in a normal healthcare wash load) are available, using marker bacteria (typically Enterococcus faecium). These would be used to determine the log reduction in bacteria count actually being achieved. The pre-infected swatches are enclosed in a special semi-permeable plastic housing, which permits total measurement of both chemical and thermal disinfection. It is fabricated from di-ethyl-stilbestrol, hence the name ‘DES-Controller’.