It takes time to kill micro-organisms. Contact time, what does it mean and what else is important in the process of disinfection.
CONTACT TIME DISINFECTION
What does it mean and what else is important in the process of disinfection?
Author: Ing. Paul Harleman Global Application Manager FHCS Vileda Professional
WHAT IS A DISINFECTION PRODUCT ?
in contact with the substance for a certain period of time, result in the death or inactivation of micro-organisms. This can happen in various ways: destruction of the cell wall, dehydration of the cell wall that also causes a destruction, or disruption of the propagation process and/or metabolism of the micro-organism. FOR A CERTAIN PERIOD OF TIME, WHAT DOES THAT MEAN? Effective killing of the desired number of micro-organisms when using a disinfectant requires a certain time for the product to do what it must do. It is called the contact time. The contact time required for a particular disinfectant to do its job effectively must be proven by the product manufacturer according to standard procedures and indicated on the product information (like e.g. the label and product documentation). Proving the efficiency of a disinfection product is by the way also necessary for the mandatory product registrations like e.g. the European BPR (1) or American EPA (2) .
Disinfection products belong to the group of biocides and aim to reduce the number of (pathogenic) micro-organisms on a surface to an acceptable level. Acceptable in this case means that there is no longer a risk of contamination. Disinfection is defined as killing or inactivating micro-organisms. The European “Biocidal Products Regulation” even gives a somewhat broader definition: “Active substance and preparation which, in the form they are supplied to the user, contain one or more substances intended to destroy a harmful organisms, deter them, render them harmless, prevent their effects or otherwise by chemical or biological means.“ It should be noted that this definition does not include physical disinfection, which in itself is logical from the perspective of the biocides legislation.
CHEMICAL, PHYSICAL OR BIOLOGICAL DISINFECTION Broadly speaking, there are three main
forms
to biological. Chemical disinfection products contain substances that, when disinfect: chemical, physical or
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DRY OR WET? If you moisten a surface with a disinfection product, the liquid film will air dry for a certain time. During this process the product is effective. The question is whether it still works once the surface is dry? And is the contact time specified by the manufacturer, the time between the wet and dried surface (wet contact time) or does a certain time span also count as long as the dried product is effective,...if at all. This is important because the latter is difficult to prove and there is very limited scientific research available. One of the few studies related to this subject is, for example, a study published in 2021 (3) on the bactericidal effect of “ready-to-use” disposable disinfection wipes, concludes that there is no additional bactericidal effect after drying of the disinfectant liquid film. WET CONTACT TIME IS WHAT COUNTS From the above, it is clear that the contact time specified by the manufacturer refers to the wet contact time. There are US and European guidelines that either do not mention contact time at all or talk about contact time but do not define the term. However, most organizations advising the pharmaceutical industry define the term as wet contact time: the time between the, visually observed, moist and dried surface.
WHAT DRIES UP FIRST IS DEC I S I VE
When using a disinfectant, the contact time prescribed by the manufacturer should be respected. Slightly longer is not a problem, shorter is not acceptable. Otherwise, there is a risk of not killing enough micro-organisms and the contamination risk is not, or not sufficiently, eliminated. As mentioned above, the contact time is simply the drying time of the disinfectant liquid film applied to the surface. However, a surface is never completely dry from one moment to the next which makes it a bit more difficult. For that reason, common sense tells us that the first part of the floor that dries determines wether you have met the contact time. The rest of the surface will have a slightly longer contact time, but at least you can be sure that entire surface is disinfected properly. Seems logical to me I would say.
“ There are American and European guidelines that do not talk about contact time at all or where they do talk about contact time, but then fail to define the term. “
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BY THE WAY •
touching the entire surface and respecting the prescribed contact time. • Unnecessary disinfection, excessive disinfection or improperly performed disinfection can lead to major problems in the short and long term. There are indica- tions that the long-term effect could be that certain mi- cro-organisms become resistant to certain disinfectants. Scientists all over the world are increasingly concerned with this emerging problem as well as govermental health organizations. The Dutch Health Council pub- lished an interesting study with recommendations on this in 2016 (4) called “Careful use of disinfectants”. Contact time is only one aspect that matters for proper dis- infection. But it is not just that. Disinfection is a serious job that requires expertise and care. For both cleaning and disin- fection, rushing through the job is not desirable, but we must realize that careless disinfection can have much greater con- sequences than careless cleaning. Cleaning and disinfect- ing is a profession, that’s what it ultimately comes down to.
The purpose of disinfecting is not the same as the pur- pose of cleaning. Cleaning aims to remove dirt so that the surface is optically clean. Disinfecting aims to kill or inactivate micro-organisms on the surface so that it is hygienically clean. When you clean with high quality microfiber cloth or mop and water only, you can remove up to 99,99% of the micro-organisms together with the dirt. Several cloths and mops of Vileda Professional are tested and certified by an independent institute on this characteristic. The micro-organisms did not die so disinfection can not be claimed, but nevertheless you can claim that the surface is not only optically but also hygienically very clean. • The standard procedure for surfaces to be disinfected rec- ommended by most infection control experts is a 3-step procedure: 1. Absorb the (body) fluid (if applicable) 2. Clean 3. Disinfect This takes time and therefore, among other reasons, there are also products on the market that allow cleaning and disinfection in one operation. Under strict conditions infection prevention experts might approve this proce- dure as an alternative to the standard procedure. Just a small note on the 3-step procedure. After cleaning and before disinfecting, the surface must be completely dry. If it is not, you dilute the disinfectant and the efficacy of the disinfectant may be less. • Disinfection only gives the desired result if it is per- formed correctly. Think for example of the exact dosage,
NOT E S (1) BPR = Biocidal Products Regulation (2) EPA = Environmental Protection Agency (3) Alyssa M. West et al (2021)
There is no additional bactericidal efficacy of Environmental Protection Agency–registered disinfectant towelettes after surface drying or beyond label contact time (ajicjournal.org) (4) Dutch healthcouncil, Careful use of disinfectants (2016) https://www.healthcouncil.nl/documents/advisory-re- ports/2016/12/21/careful-use-of-disinfectants
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