Effective disinfection of surfaces, instruments and hands has always been critical to minimise infection risks in dental practices. Given the current Covid-19 situation, infection prevention measures will be paramount as practices begin to reopen for routine dentistry. In the current climate, selecting the most appropriate disinfectants and using them correctly will play a vital role.
The main function of a disinfectant lies in its ability to eliminate or inactivate microorganisms. Therefore, a key step in the selection process is ensuring the disinfectant has the required level of biocidal activity.
Disinfection manufacturers provide efficacy data relating to the two key criteria of contact time and required concentration. This data should be based on product testing which is both rigorous and repeatable. In Europe, this means being tested to the European Norms (EN), which remain the ‘gold standard’ tests for disinfectants in the UK. These standards have a number and are ‘version controlled’ by the stated year.
European standards for testing disinfectants are based on test methods orientated towards the practical use of the disinfectant. Agreed standards ensure that manufacturers are able to validate claims of bactericidal (including tuberculocidal) and virucidal activity. Theoretically, these standards should allow the direct comparison of disinfectants from different manufacturers, as they should have been tested using the same standard under the same test conditions.
Standards are regularly reviewed and updated, but it is not mandatory for a disinfectant manufacturer to test to the latest standards. For example, the standard EN13624:2003 specifies the minimum requirements for fungicidal or yeasticidal activity of chemical disinfectants in the healthcare setting. The 2003 version was superseded by EN13624:2013, which specifies more rigorous efficacy testing. In practice this means that a disinfectant tested to the 2013 EN would need to be used at an increased concentration and/or a longer contact time, than if it were tested to the 2003 standard. If comparing two disinfectants and one was tested to EN13624:2003 and the other to EN13624:2013, an accurate comparison could not be made in terms of concentration or contact times required. Also, a disinfectant that has only been tested against the 2003 standard is not necessarily as efficacious for use within the dental practice.
There is no mandatory requirement for an updated standard to be adopted by a manufacturer within a set period of time (or to be reassessed at all). As standards become increasingly rigorous, to protect both patients and staff, there appears to be little incentive for disinfectant manufacturers to test to newer, tougher standards, which could mean increased disinfectant concentration times and longer contact times, to ensure microbial efficacy.
However, there are some manufacturers who will always adopt and test to the latest norms, to ensure the highest infection prevention standards are maintained, but this may require a little research to ensure disinfectant claims are truly comparable.
For dental practice use, there are a number of relevant standards which disinfectants may be tested against.
EN13624:2013 – evaluation of fungicidal or yeasticidal activity, supersedes EN 13624:2003.
EN13727:2012+A2:2015 – evaluation of bactericidal activity, supersedes EN 13727:2003.
EN 14476:2013+A2:2019 – evaluation of virucidal activity, including coronaviruses, so is of critical importance.
EN 17126:2018 – evaluation of sporicidal activity.
These European standards apply to products including hygienic hand rub, surgical hand rub, surgical handwash, instrument disinfection by immersion, and surface disinfection by wiping, spraying, flooding, or other means. They are applicable to situations where disinfection is medically indicated, such as in a dental practice.
When it comes to the selected disinfectant, the two key variables to consider are the disinfectant concentration and the contact time. Both of which significantly affect the efficacy of the disinfectant.
Disinfectant concentration
Disinfectant concentration affects the level of microbicidal efficacy achieved. The setting of this concentration range depends on factors such as contact time, material compatibility and biocidal activity. The mode of action of disinfectants can vary with concentration. 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 eliminate it, known as the ‘contact time’.
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. 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. 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.
Changes to disinfectant test standards and why these matter
Two key standards applicable to dental practice disinfection have been updated. EN13624:2003 has been superseded by EN13624:2013 and EN13727:2003 superseded by EN13727:2012+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 per cent 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 two per cent concentration with a 15-minutes contact time or a four per cent concentration at five-minutes 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) 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 (including virucidal properties) and how effectively they are used.
References available on request.