INFECTION CONTROL
disinfectants can vary with concentration. Bactericidal (kills bacteria) disinfectants can become bacteriostatic (inhibiting the 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 eliminate it, known as the ‘contact time’.4
Contact times are related
to the concentration of the disinfectant. 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.4
It is important that
contact times have been correctly assessed and are complied with. Contact times can also be influenced by the type of soiling. Although disinfectants are evaluated under ‘dirty’ conditions, the presence of dirt can significantly reduce their efficacy.5
Therefore, a pre-cleaning
step before disinfection should always be undertaken. This helps to physically remove soiling like visible dirt and protein residues, which could create barriers to the disinfectant contacting pathogens.6
Changes to test standards and why these matter 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 EN 13624:2003 has been superseded by EN 13624:2013, and EN 13727:2003 superseded by EN 13727:2012+A2:2015. The updated ENs contain important modifications which have a major impact on how disinfection concentration and contact times are evaluated. For example, the old standards required an evaluation of a 1.5% concentration of a particular disinfectant, together with a five-minute 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-minute contact time, or a 4% concentration at a five-minute contact time to achieve a ‘pass’.
The updated standards are more scientifically accurate, and 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, the first step should always be to check that the chosen product(s) have been tested to the most up-to-date standards. The risk of selecting disinfectants tested to the older (superseded)
60 Health Estate Journal July 2020 European Norms remain the ‘gold standard’ when selecting disinfectants for UK use.
standards may mean that concentrations are too weak, and/or that 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 (including virucidal properties), and how effectively they are used.
3 West AM, Teska PJ, Lineback CB, Oliver HF. Strain, disinfectant, concentration, and contact time quantitatively impact disinfectant efficacy. Antimicrob Resist Infect Control 2018; 7: 49.
4 Rutala WA, Weber DJ. Surface Disinfection: Treatment Time (Wipes and Sprays) Versus Contact Time (Liquids). Infect Control Hosp Epidemiol 2018; 39 (3): 329-331.
hej
References 1 Fraise, AP (2008) European norms for disinfection testing. J Hosp Infect 2008; 70 (S1): 8–10
2 Langsrud S, Sundheim G. Factors influencing a suspension test method for antimicrobial activity of disinfectants. J Appl Microbiol 1998; 85: 1006-12.
Tim Sandle
Dr Tim Sandle is a chartered biologist (Royal Society for Biology), and holds a first-class honours degree in Applied Biology and a Master’s degree in education; he obtained his doctorate from Keele University. He is an honorary tutor with the School of Pharmacy and Pharmaceutical Sciences at the University of Manchester. He serves on several national and international committees relating to pharmaceutical microbiology and cleanroom contamination control, and has written over 500 book chapters, peer-reviewed papers, and technical articles relating to microbiology, healthcare, and pharmaceutical science. He has also delivered papers to over 100 conferences. Dr Sandle is the editor of the Pharmaceutical Microbiology Interest Group journal, and runs an on-line microbiology website and forum (
www.pharmamicroresources.com).
5 Johnston MD, Simons E-A, Lambert RJW. One explanation for the variability of the bacterial suspension test. J Appl Microbiol 2000; 88: 237-42.
6 Hall L, Mitchell BM. Cleaning and decontamination of the healthcare environment. In: Walker J ed. Decontamination in Hospitals and Healthcare. Woodhead Publishing: Cambridge, 2020; 227-39.
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
