INFECTION CONTROL


chemicals in disinfectants may be categorised into groups based on their chemical nature, spectrum of activity, or mode of action. Effectiveness is assessed through disinfectant efficacy testing, but a problem faced when selecting a disinfectant is the array of different standards. This is where the EU standards have a useful role to play, although some understanding of them is required if they are to be used as the basis for disinfection selection.


Disinfectant standards are required for several reasons. They prevent manufacturers from claiming activity in a product which is not, in fact, a disinfectant. For example, distilled water lyses many bacteria, and therefore does have some very limited bactericidal effects, but it could not be described as a disinfectant.1 There are a number of European testing standards (EN standards) that are currently available, including both suspension testing methods – which test the ability of a disinfectant to kill microorganisms in a liquid suspension, and surface/carrier testing methods – which test the disinfectant’s ability to kill microorganisms dried onto a surface. Both test types demonstrate if the disinfectant contact time and concentration are appropriate.


Use of accredited laboratories It is vital that manufacturers have performed disinfectant testing in accredited laboratories with experience performing this type of rigorous and specific testing. For example, if disinfectant neutralisation is not performed correctly, the actual contact time required will be longer than the published contact time. This means that the efficacy of the disinfectant may have been overestimated.


When reviewing a disinfectant for use in the hospital environment, it is worth asking: n Is it biologically plausible that this disinfectant chemistry will have the level and range of biocidal activity being claimed? For example, only a relatively few disinfectant chemistries have meaningful sporicidal activity (generally chlorine, hydrogen peroxide, or peracetic-acid based ones).


n Was an appropriate testing standard used? For example, a suspension test (such as EN 13727:2012) does not provide good evidence that a disinfectant will be active against bacteria dried onto surfaces; instead, a carrier test (such as EN 13697:2015) should be used in addition.


n Were the tests performed in an accredited, experienced laboratory that has produced a report with a sufficient level of detail? If not, biocidal efficacy could be over-estimated.


For hospital use, there are a number of


applicable standards which manufacturers of disinfectants should be testing against: n EN 13624:2013, ‘Chemical disinfectants and antiseptics. Quantitative suspension test for the evaluation of fungicidal or yeasticidal activity in the medical area’. This supersedes EN 13624:2003;


n EN 13727:2012+A2:2015, ‘Chemical disinfectants and antiseptics. Quantitative suspension test for the evaluation of bactericidal activity in the medical area’. This supersedes EN 13727:2003;


n EN 14476:2013+A2:2019, ‘Chemical disinfectants and antiseptics: Quantitative suspension test for the evaluation of virucidal activity in the medical area’.


n EN 17126:2018, ‘Chemical disinfectants and antiseptics. Quantitative suspension test for the evaluation of sporicidal activity of chemical disinfectants in the medical area’.


These European Standards apply to products that are used in the medical area in the fields of hygienic hand rub, surgical hand rub, surgical handwash, instrument disinfection by immersion, and surface disinfection by wiping, spraying, flooding, or other means. They apply to areas and situations where disinfection or antisepsis is medically indicated. The basic requirement is at least a 5-log reduction of vegetative microbial cells under EN 13624 and EN 13727, and a 4-log reduction for bacterial spores under EN 17126 (since spores are harder to kill).


The suspension test to evaluate disinfectant efficacy


The disinfectant efficacy validation aims to provide documented evidence that the disinfectant demonstrates the virucidal, bactericidal, fungicidal, and/or sporicidal


activity necessary to control microbial contamination in general, and to eliminate pathogens of concern. The purpose of the quantitative suspension test, as set out in the above standards, is to evaluate the activity of a given disinfectant against a range of microorganisms under conditions that closely simulate the practical use of the disinfectant. Suspension tests require the disinfectant to be of a certain concentration, and to be evaluated for a controlled period of time. This assesses how the disinfectant is presented in practice, and for how long it needs to be applied. In addition, the disinfectant is made up in the ‘worst case’ condition by using ‘water of standard hardness’ (which contains ions like magnesium and calcium, as well as other salts). A further condition is the simulation of ‘soiling’ (‘dirty’ conditions), which is achieved by the addition of bovine serum albumin at 0.03%, representing ‘clean’ conditions, and at 0.3% representing ‘dirty’ conditions.2


To demonstrate the


effectiveness of a disinfectant, the product must be challenged using a panel of microorganisms that are reflective of the clinical setting.


Two key variables to consider When it comes to the selected disinfectant, the two key variables to assess under the suspension test are the disinfectant concentration and the contact time.


Disinfectant concentration Disinfectant concentration affects the level of microbicidal efficacy achieved.3 The setting of this concentration range depends on factors such as contact time, material compatibility, and biocidal activity. The mode of action of


It is vital that manufacturers have performed disinfectant testing in accredited laboratories with experience of performing this type of rigorous and specific testing.


July 2020 Health Estate Journal 59


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