Getting real with disinfectant concentration and contact time


The processes in place for establishing whether a hospital disinfectant is suitable for use in a clinical setting have been around for a long time – but do they remain fit for purpose? A recent study shows that disinfectant concentration and contact time can be reduced without negatively affecting efficacy – but not too much!

Tests with unrealistically long contact times, high concentrations of disinfectant, and performed in suspension rather than on a hard substrate are not helpful in establishing whether a disinfectant is suitable for use in the clinical setting. Equally, laboratory disinfectant testing needs to be performed with a worst-case scenario in mind. A recent study ‘stress tested’ the parameters for the laboratory testing of a selection of hospital disinfectants, reducing the disinfectant concentration and contact time. The disinfectants tested were accelerated hydrogen peroxide, quaternary ammonium compounds (QACs), and sodium hypochlorite. There was a degree of tolerance to reducing contact time and disinfectant concentration. The study found that bactericidal efficacy was not reduced when contact times or concentrations were reduced to just below label use values. However, all of the disinfectants were significantly less bactericidal when contact times and concentrations were reduced substantially. The sodium hypochlorite was most tolerant to changes in contact time and concentration.

This study is useful and suggests that contact times and disinfectant concentrations could be reduced in some settings. However, there are many drivers of the efficacy of a disinfectant, including soiling, the presence of biofilms, and stability of the disinfectant. Therefore, laboratory studies need to be complemented by real-world studies in the clinical setting to establish the suitability of disinfectants for surface disinfection in hospitals.


VRE lurking in the ICU environment


An Irish study has identified an established VRE environmental reservoir in the ICU, outside of an outbreak setting. VRE was identified from the ICU environment on 30% of 289 sampling occasions, and a number of patient-environment clusters were identified through molecular typing. A keen focus on the contaminated environment is vital for effective prevention of VRE transmission.

VRE is a Gram-positive pathogen with the capacity to survive on dry environmental surfaces for literally years. There is strong epidemiological evidence that the contaminated environment contributes to the transmission of VRE in clinical settings: being admitted to a room previous used by a patient increases the risk of the next occupant of the same room acquiring VRE.

This study from Ireland presents a comprehensive survey of patient colonisation and environmental contamination with VRE. The team launched an active surveillance programme for VRE colonisation and also took the opportunity to perform prospective surveillance of the environment. VRE colonisation of patients and the environment was common, being detected on 30% of the sampling occasions. Of the 1,647 environment samples collected, 107 sites (6.5%) grew VRE; VRE was (unsurprisingly) more common in isolation rooms (9%) than in open-plan areas (4%). However, the frequent discovery of VRE outside of isolation rooms is concerning. Genotying of the isolates involved identified likely transmission from patients to the environment, and from the environment to patients.

These findings reinforce the importance of contamination of the hospital environment in the transmission of VRE, and argue for enhanced cleaning and disinfection to reduce VRE transmission.


Neutralising duff “sporicidal” claims of amine-based disinfectants

There is a lot of value to a disinfectant manufacturer of having a sporicidal claim so that the product can be used in healthcare settings to tackle C. difficile spores. However, not all products with a sporicidal claim are in fact sporicidal! Amine-based disinfectants with “sporicidal” claims are being seen increasingly in the marketplace, but these products are unlikely to have meaningful sporicidal activity, as highlighted by a recent letter in the Journal of Hospital Infection.

We posted recently on the questions to ask of products claiming to have sporicidal activity: does the testing match the proposed usage, is the contact time representative of in-use recommendations and practice, has the disinfectant been neutralised effectively in laboratory tests, and was the testing performed in a reputable laboratory? One of the key steps in laboratory disinfectant testing is the neutralisation step. This nullifies the activity of the disinfectant so that an exact contact time can be measured. If this step isn’t completed correctly, the disinfectant continues to work beyond the planned contact time, and efficacy can be over-estimated.

One of the main culprits of sporicidal claims that we believe to be misleading are amine-based disinfectants. Prof Jean-Yves Maillard, a world-renowned expert in disinfectant testing, has written a letter in the Journal of Hospital Infection highlighting the challenge of inappropriate neutralisation in laboratory testing resulting in inaccurate “sporicidal” results for these amine-based disinfectants. The lack of a recognised European sporicidal test is a limitation, and so a UK-developed sporicidal testing standard for C. difficile (with an appropriate neutralisation step!) should be considered the gold standard. And no amine-based disinfectants have passed this test. Therefore, we agree with Prof Maillard, that it is puzzling and concerning that products containing solely amines are being used as sporicides in healthcare settings.


UV light vs. Candida auris


A US study has found that Candida auris exhibited a similar level of susceptibility to UV light as Clostridium difficile spores, and was considerably less susceptible than MRSA. These findings suggest that either extended exposure UV cycles or hydrogen peroxide based room disinfection are required to address environmental contamination with Candida auris.

We have posted before on the efficacy of various disinfectants against Candida auris, supporting that chlorine-based disinfectants and chlorhexidine have a role to play in preventing the transmission of Candida species. This latest laboratory study tested the efficacy of a UV room decontamination system against various species of Candida auris and Candida albicans, MRSA, and C. difficile spores. Metal discs with these organisms dried onto them were placed 5 feet from the device at a height of 4 feet with exposure times of 10, 20, or 30 minutes. UV achieved a <2-log reduction on C. auris after 10 minutes of exposure (vs. a >6-log reduction for MRSA), a 4-log reduction after 20 minutes, and a 6-log reduction after 30 minutes. The efficacy profile of UV against C. difficile and C. auris was similar.

This study is in line with the findings of others that C. auris is able to less susceptible to disinfection than other agents. Therefore, extended exposure UV cycles or hydrogen peroxide based room disinfection should be used to tackle environmental contamination with C. auris.


Chlorhexidine beats povidone-iodine in preventing vascular catheter colonisation

An impressive randomised multi-centre study in Japan has evaluated the efficacy of 0.5 and 1% alcohol/chlorhexidine with 10% povidone-iodine in preventing colonisation of vascular catheters. The study concluded that chlorhexidine at either concentration is superior to povidone-iodine in preventing the colonisation of vascular catheters.

The study was performed in 16 Japanese intensive care units. The 796 central venous or arterial catheters included in the final analysis were randomised to 0.5% and 1% alcohol/chlorhexidine with 10% povidone-iodine during insertion and dressing changes. Catheter-tip colonisation was 3.7 events per 1000 catheter-days in the 0.5% chlorhexidine group, 3.8 in the 1% chlorhexidine group, and 10.5 in the povidone-iodine group. The rate of catheter-tip colonisation was statistically significantly lower in both chlorhexidine groups compared with the povidone-iodine group.

It’s important to note a couple of limitations in this study. Firstly, the authors compared chlorhexidine in alcohol with a povidone-iodine solution. So it isn’t possible to disentangle the effect of alcohol from chlorhexidine using this design. Secondly, although the authors tested two concentrations of chlorhexidine (0.5% and 1%), both are lower than would usually be used in clinical settings in most parts of the world (2%). Thirdly, there was no impact on the rate of catheter-related bloodstream infections between the two groups, although this may be a factor of sample size, because the primary outcome, for which the study was powered, was catheter tip colonisation.

Despite these limitations, the findings of this large randomised trial are compelling, finding that vascular line-tip colonisation is less than half as likely when chlorhexidine is used during insertion and ongoing line care compared with povidone-iodine. This reinforces that chlorhexidine is a better choice than povidone-iodine for skin decontamination during line insertion and ongoing line care in the ICU setting.




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