INF ECT ION PR EVENT ION & CONT ROL
the two key variables to assess under the suspension test are the disinfectant concentration and the contact time.
Disinfectant concentration Disinfectant concentration affects the microbicidal efficacy achieved5
13727:2012+A2:2015. The setting of
this concentration range depends on factors such as contact time, material compatibility and biocidal activity.
The higher a disinfectant’s concentration exponent (the relationship between dilution and biocidal activity), the longer it will take to kill cells. Concentrations that are lower than the label-use have been shown to not be as effective. For example, if a disinfectant with a set concentration exponent was diluted by a factor of two, the time taken for it to kill cells comparatively may double. The mode of action of disinfectants can vary with concentration and, for example, bactericidal (kills bacteria) disinfectants can become bacteriostatic (inhibits growth of bacteria) if overdiluted, potentially allowing pathogens to survive and increase in numbers.
Contact times
Each chemical disinfectant requires a period of time during which it needs to be in contact with the microorganism to inactivate or kill it. This is known as the ‘contact time’.6 Contact times are related to the concentration of the disinfectant and are expressed for each disinfectant at its optimal concentration range. The killing effect for a constant concentration of a disinfectant increases over time until the optimal contact time is established. This needs to take place before the disinfecting solution dries and before patients or staff are likely to retouch the surface.6 It is important that contact times have been correctly assessed and are adhered to, since reduced contact times are less effective against microorganisms, which may lead to a high proportion of pathogens surviving.7 Contact times can also be influenced by the nature of soiling. Although disinfectants are evaluated under ‘dirty’ conditions, the presence of dirt can significantly reduce their efficacy.8
Therefore a pre-cleaning
step before disinfection should always be undertaken. This helps to physically remove soiling like visible dirt and protein residues. Pre-cleaning removes any barriers to the disinfectant contacting the microbial cell wall.9
Changes to disinfectant test standards and why these matter As mentioned previously, two key standards applicable to hospital disinfection have been updated. EN 13624:2003 has been superseded by EN 13624:2013 and EN 13727:2003 superseded by EN
OCTOBER 2020
The updated ENs contain important modifications which have a major impact on how the concentration and contact times are evaluated. To meet these new standards, three disinfectant concentrations are required to be assessed during the suspension tests. This is to cover the active and non-active range of the product. It aims to provide some control on the test method and ensure that the final product will work effectively. The non-active concentration would be expected to fail the test.
This relationship matters because the relationship between concentration and efficacy of disinfectants is exponential, meaning that changes in concentration (or dilution) affect the cell death rate. Disinfectants have different concentration exponents and relatively small changes in concentration could be significant in terms of how effective the disinfectant is. To give an example of how this works in practice, the old standards required an evaluation of a 1.5% concentration of a particular disinfectant together with a 5-minutes contact time in order to achieve a ‘pass’. Whereas testing exactly the same disinfectant to the updated standard requires the use of a 2% concentration with a 15-minutes contact time or a 4% concentration at 5-minutes contact time to achieve the minimum log-reduction of the microbial challenge.
The updated standards are more scientifically accurate. They demonstrate the actual contact time and concentration required to kill a known population of pathogens. There can be significant differences between various disinfectant concentrations and contact times in terms of efficacy. Therefore, before selecting any disinfectant for use in a healthcare environment, the first step should always be to check that the chosen product(s) have been tested to the most up to date standards - EN 13624:2013, EN 13727:2012+A2:2015, EN 14476:2013+A2:2019 and EN 17126:2018.
Selecting disinfectants tested to the older (and now out of date) standards may mean that concentrations are too weak and/ or contact times are too short to ensure that pathogens have been eradicated or inactivated to the degree they no longer pose a threat to health.
In the current climate of the COVID-19 pandemic, risks cannot afford to be taken when it comes to the choice of disinfectants (such as viricidal properties) and how effectively they are used.
References 1 Fraise, A.P. (2008) European norms for disinfection testing. Journal of Hospital Infection 70(S1) 8–10
2 Bloomfield, S. F., Arthur, M., Begun, K. and Patel, H. (1993) Comparative testing of disinfectants using proposed European surface test methods,’ Letters in Applied Microbiology, 17: 119-125
3 Sandle, T. (2006): Selection of Laboratory Disinfectants, The Journal, Institute of Science Technology, Summer 2006, pp16-18
4 Langsrud, S. and Sundheim, G. (1998) Factors influencing a suspension test method for antimicrobial activity of disinfectants,’ Journal of Applied Microbiology, 85: 1006-1012
5 West AM, Teska PJ, Lineback CB, Oliver HF. (2018) Strain, disinfectant, concentration, and contact time quantitatively impact disinfectant efficacy. Antimicrob Resist Infect Control.;7:49
6 Rutala, W. A. and Weber, D. J. (2018) Surface Disinfection: Treatment Time (Wipes and Sprays) Versus Contact Time (Liquids), Infection Control & Hospital Epidemiology, 39 (3): 329-331
7 Hong Y, Teska PJ, Oliver HF. (2017) Effects of contact time and concentration on bactericidal efficacy of 3 disinfectants on hard nonporous surfaces. Am J Infect Control.;45:1284–5
8 Johnston, M. D., Simons, E.-A. and Lambert, R. J. W. (2000). One explanation for the variability of the bacterial suspension test. Journal of Applied Microbiology, 88: 237 – 242
9 Hall, L. and Mitchell, B. M. (2020) Cleaning and decontamination of the healthcare environment. In Walker, J. (Ed.) Decontamination in Hospitals and Healthcare, Woodhead Publishing, Cambridge, pp227-239
About the author CSJ
Dr. Tim Sandle is a pharmaceutical microbiologist, science writer and journalist. He is also a tutor with the School of Pharmacy and Pharmaceutical Sciences, University of Manchester for the university’s pharmaceutical microbiology MSc course, and he lectures on sterile products at University College London. In addition, Dr. Sandle has served on several national and international committees relating to pharmaceutical microbiology and cleanroom contamination control (including the ISO cleanroom standards and the National Blood Service advisory cleaning and disinfection committee).
WWW.CLINICALSERVICESJOURNAL.COM l 37
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92
