Self-disinfecting surfaces: promising but not there yet

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A recent JHI study highlights both the promise and limitations of self-disinfecting surfaces. The study evaluated the efficacy of five different self-disinfecting surfaces against S. aureus under simulated real-life conditions. The small antimicrobial effects noted initially disappeared once most of the surfaces began being cleaned using alcohol wipes!

The team examined the efficacy of five self-disinfecting surfaces: a micro-patterned film (based on Shark skin to reduce bacterial adhesion), and four surfaces dosed with antimicrobial agents: zinc molybdenum (ZM), polyguanidin silica (PS) and two based on membrane-active polycations (maPK-I and maPK-a). A bacterial load of 8-log cfu was applied and then dried, before being sampled at 15 mins and 3 hours using contact plates. Only the MP, maPK-I and maPK-a based surfaces resulted in a reduction in bacterial contamination. The antimicrobial impact of MP and maPK-i disappeared after a single disinfection cycle, so were not stable enough to be useful. However, the maPK-a surfaces continued to exhibit an antimicrobial impact but only up to 19 disinfection cycles.

The inoculum used in the study was rather high (at 8-log), and probably not representative of the real-life environment, where contamination levels are usually lower. Also, the first exposure point tested was 15 minutes, whereas more rapid activity would be a favourable characteristic for a self-disinfecting surface: after all, how long does it take for a transmission to occur? Finally, the study only included S. aureus and, importantly, did not include C. difficile spores; sporicidal activity would be a huge plus for a candidate self-disinfecting surface.

The study used copper alloy surfaces as a control group, and based on these results, copper surfaces remain the prime candidate for antimicrobial surfaces. However, installing copper alloy surfaces is expensive, not suitable for all surfaces / equipment, and may not be durable in the clinical environment. Therefore, further development is required to achieve a low cost, high efficacy, durable self-disinfecting surface suitable for use in the clinical environment.

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Reducing Aspergillosis in neutropaenic patients using a stand-alone air handler

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Neutropaenic patients are susceptible to fungal infection, which are extremely difficult to treat and can often be fatal. The problem is that fungi are all around us – especially in the air. This isn’t a problem for healthy people, but can be a major problem for neutropaenic patients, who have a low white cell count so struggle to fight infection. An emerging approach to this problem is the use of stand alone air handlers to reduce the amount of fungi in the air. A recent study shows that this approach significantly reduced the rate of Aspergillosis in neutropaenic patients.

The study was performed over two years in patients with chemotherapy-induced neutropaenia in a haematology ICU. Half of the 15 bed unit was fitted with Plasmair air decontamination units. Regular environmental sampling demonstrated a significant reduction in air contamination above 5 cfu/m3 (7% vs. 19%), and particle count above 350,000 per m3 (4% vs. 93%). There was also a non-significant reduction in surface contamination in Plasmair-containing rooms. More importantly, there as a significant reduction in the rate of Aspergillosis in patients admitted to Plasmair-containing rooms (1 case) vs. non-Plasmair-containing rooms (10 cases) (odds ratio 0.11, 95% confidence interval 0.00-0.84).

The study isn’t perfect: patients were not randomised to the different rooms, and the number of clinical cases of Aspergillosis was low. However, the study does demonstrate a stark environment and clinical impact of Plasmair in patients who have chemotherapy-induced neutropaenia.

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Hydrogen peroxide versus bleach; who wins?

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A randomised multicentre trial in Italy published this month in the Journal of Hospital Infection has examined the effectiveness of automated hydrogen peroxide (AHP) supplemented with silver ions, and 5,000 ppm sodium hypochlorite (bleach) on Clostridium difficile (CD). Twenty-eight rooms previously occupied by patients with C. difficile infection (CDI) at four health facilities were randomised to either AHP or sodium hypochlorite disinfection. Prior to disinfection both rooms underwent a standard operating cleaning procedure to remove visible soil. Eight high-touch locations in each room were swabbed before and after disinfection to look for the presence of CD bacteria. Prior to the disinfection phase, CD was detected in 18 of the 28 rooms (64%) sampled, the most commonly contaminated sites being the light switch, nursing call device and the bedside table. This agrees with several other studies which have highlighted the presence of CD in the environment following discharge of CD positive patients.

Both disinfection methods were shown to significantly reduce CD contamination in the rooms, 50% contamination pre and 0% post decontamination in the HP arm and 79% contamination pre and 14% post decontamination in the bleach arm, although there was no statistically significant difference, probably because of the small sample size. The unblinded nature of the study means that housekeeping staff were aware that sampling was taking place and may have changed the way they approached the disinfection procedure in the bleach arm in order to compete with the automated system. We presume also that researchers carrying out the sampling were also aware of the disinfection methods as blinding is not referred to in the paper. Another interesting finding was that the average total time from a patient leaving a room to it being available for the next occupant was slightly longer with sodium hypochlorite in comparison to HP procedure, again possibly due to thoroughness of the staff cleaning with Chlorine as the average disinfection process for a room with Chlorine was 119 minutes.

The study highlights that both methods were effective at reducing CD contamination to a point, however it is interesting that even after a decontamination process that took nearly two hours, a significant number of rooms (14% in this case) remained positive post decontamination in the Chlorine arm, thus continuing to pose a risk to the next occupant. Additionally, a more detailed description of the bleach-based disinfection method used in the study would help the reader to interpret the results in the context of routine practice in the UK NHS. In addition, presenting clinical infection rates alongside these laboratory results would provide a valuable association with important clinical effectiveness outcomes.

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Could you wipe away viral illness at home?

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An interesting study published a couple of years ago showed that transmission of bacteriophage used as a surrogate for respiratory viruses was reduced significantly by introducing a once-per-day hand wipe in the home environment. Could this suggest that hand wipes have a role in reducing viral illness at home?

Five households, each containing two adults and three children, were included in the study. A female adult’s hands were inoculated with a high concentration of a non-pathogenic marker of virus spread: a common bacteriophage. The hands of all household members and surfaces in the house were then sampled 8 hours later to see how far the virus had spread. The process was then repeated, but this time with each household member asked to wipe their hands at least once per day with a sanitising wipe, in addition to normal hand washing with soap and water. The wipe intervention was associated with a significant reduction in contamination of the hands of the inoculated individual, and surfaces in the house. There was a non-significant reduction in contamination of non-inoculated hands.

The group then applied these findings to the potential transmission of key viruses, rhinovirus and rotavirus, concluding that there would be a 30-90% reduction in transmission risk of these viruses through a hand wipe intervention.

This study certainly supports the benefit of an increased frequency of hand cleansing in the home environment. The intervention could just as easily have been at least one extra hand wash per day using soap and water. However, a hand wipe provides convenience and accessibility that will almost certainly result in more hand cleansing being done!

Whilst the transmission of a bacteriophage may not follow the same dynamics as the transmission of a pathogenic virus, this study certainly provides compelling data in line with other studies that a hand wipe intervention in the home environment could help to prevent viral illness.

 

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Quats vs. hydrogen peroxide vs. VRE

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A Dutch laboratory evaluation of four different disinfectant applied by either spraying or wiping has found that most are effective against key hospital pathogens. However, the hydrogen peroxide spray was ineffective against VRE, suggesting a problem with hydrogen peroxide stability.

The study tested the ability of a hydrogen peroxide solution (branded a sporicidal), QAC, alcohol, and glucoprotamin to inactivate clinical isolates of VRE, K. pneumoniae, and A. baumannii. The products were applied as either a spray or wipe following a 1 hour contact time.

All disinfectants achieved a >5 log reduction on the organisms tested, with the exception of hydrogen peroxide sprayed onto VRE. Now, hydrogen peroxide is very effective against enterococci, so I suspect that this illustrates a problem with instability of the hydrogen peroxide in the disinfecant formulation.

It is also worth noting that the long contact time (1 hour) is not representative of the real world application of these products, where a 1 minute contact time would be more appropriate!

This study provides further evidence that QACs (the key active ingredient of Clinell Universal wipes) can be used to provide stable and effective disinfectant wipes.

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