There’s an emerging global epidemic of Mycobacterium chimaera infections following cardiothoracic surgery associated with contaminated heater-cooler units (machines that are used in theatre during some procedures). It has been established that water within the machines can become contaminated with Mycobacterium species, and that this can create a bio-aerosol that finds its way into the surgical field and causes an infection. However, a recent study from Hong Kong highlights the potential for surfaces on the heater-cooler units to be reservoirs for Mycobacterium.
The study was performed as part of an investigation into a string of cases of Mycobacterium chimaera surgical infections following cardiac valve replacement. The investigation discovered, as with many others around the world, that the water reservoir within the machines was contaminated with M. chimaera before and after disinfection of the water, providing a plausible source for the surgical infections.
However, the authors went further, and performed sampling of the surfaces on the inside and the outside of the heater-cooler units. No contamination of the outside surfaces of the units, which were effectively disinfected using Clinell Universal Wipes, was identified. However, 4/8 (50%) of the inner surfaces of the units were contaminated with M. chimaera. It’s possible that this surface contamination could be involved, either directly or indirectly, in seeding the airflow exiting the units that then enters the surgical field and causes a surgical infection. For example, M. chimaera is eliminated successfully from the water reservoir within a unit, contamination of the internal surfaces of the unit could then decontaminate the water reservoir!
This is the first study (that we’ve come across) exploring surface contamination with M. chimaera in the context of heater-cooler units used for cardiothoracic surgery. The findings certainly raise some important questions and warrant further investigation. It was reassuring that no contamination was identified on the outer surfaces of the units. However, how much of a clinical risk does contamination of the internal surfaces of these units present? How can this be reduced or eliminated? Could vapour-phase decontamination methods such as hydrogen peroxide vapour could play a role? As the global community strives to mitigate the risk of M. chimaera infections associated with heater-cooler units, contamination of surfaces could be a new frontier!
We blogged last week about a lab study illustrating the potential for dry surface biofilms to harbour bacteria that can then be transferred via the hands of healthcare workers. This week, a new study in the Journal of Hospital Infection illustrates dramatically the scale of the problem of dry surface biofilms in hospitals: a whopping 95% of 61 surfaces tested from three UK hospital groups had dry surface biofilms, and 58% of these samples grew MRSA! We need to think of ways to tackle dry surface biofilms in hospitals.
This multicentre study involved three hospital groups in Scotland, Wales, and England. 61 surface samples were collected from various wards and other clinical areas, and tested for the presence of dry surface biofilms. Almost every single surface had dry surface biofilm present. Surprisingly, despite the variability in the types of sample included (from alcohol gel bottle tops to keyboards to note holders), the physical structure of the biofilm was similar. Oddly though, the microbial composition of the biofilms was very different in one of the hospitals, containing mainly Bacillus species DNA compared with Staphylococcus DNA predominating in the other two hospitals. Its not clear why this difference existed, but could be due to differences in cleaning and disinfection frequency, materials, or chemicals.
This helpful study guides us in moving forward to tackle dry surface biofilms on hospital surfaces. The extent of dry surface biofilms given the range in hospital and items sampled was surprising, and reinforces the need to consider biofilms when planning hospital cleaning and disinfection strategies. The finding that the structure of the biofilms was consistent across the hospitals is useful, and can feed into research and development activities to develop representative dry surface biofilm models. The heterogeneity in microbial composition of the biofilms warrants further investigation, but suggests that differences in local cleaning and disinfection strategy will influence the composition of dry surface biofilm, which could have clinical implications.
The fairly recent findings of dry surface biofilms on hospital surfaces may well prompt a new era in the discovery and development of novel hospital disinfectants and disinfection strategies configured to tackle dry surface biofilms.
We have discovered only in recent years that dry surface biofilms are commonplace on hard surfaces in hospital. A recent Australian study illustrates clearly (and alarmingly!) that bacteria can be transferred from dry surface biofilms to the hands of healthcare workers – and so probably have an important role in transmission.
This simple lab study evaluated the amount of Staphylococcus aureus that were transferred from dry surface biofilms grown on glass and plastic coupons. Volunteers pinched the coupons on which the dry surface biofilms were grown, and then touched agar plates. In order to test the possibility of sequential transfer from hands, the volunteers touched a series of 19 agar plates (without touching the coupons again).
Around 5% of the S. aureus on the coupons was transferred to volunteers hands, and 1% to the agar plates via contaminated volunteers hands. While this doesnt sound like much, when you start with a couple of million bacteria, even 1% is a significant amount of bacterial transfer (around 20,000 or 105 cells)! Worryingly, bacteria were transferred to agar plates for up to 19 sequential transfers.
The study also modelled whether detergent cleaning of the biofilms would help to mitigate the transfer of bacteria. However, in the case of the plastic coupons, wetting them with detergent actually made things worse, increasing the rate of bacterial transfer to the agar plates from 1% to 5%! Perhaps this is because the physical action of cleaning the coupons mobilised bacteria in the biofilms?
We have suspected since their discovery that dry surface biofilms in the hospital environment present a reservoir for the transmission of microbes that cause hospital infections. Although performed in a laboratory setting, this study provides compelling evidence that dry surface biofilms on hospital surfaces present a clinical risk.
An Irish study has examined whether daily bathing of patients using chlorhexidine results in a “halo” effect, in reducing environmental contamination. The study found that contamination of surfaces with VRE and ESBL Enterobacteriaceae (ESBL-E) in the near-patient environment was significantly lower when chlorhexidine bathing was in operation.
The study was performed in a 12-bed mixed speciality ICU over 20 months including 157 patients, during which daily chlorhexidine bathing was introduced. Each occupied bed was sampled twice weekly for a range of antibiotic-resistant bacteria. 9.4% of 745 surfaces sampled prior to the introduction of chlorhexidine were contaminated with VRE or ESBL-E vs. 5.0% of 958 surfaces samples after (p<0.001). There was a stark and significant reduction in contamination with VRE or ESBL-E from hand-wash basins: before the introduction of chlorhexidine, 10% of hand-wash basins were contaminated (!), which fell to <2% after chlorhexidine was introduced.
The study evaluated a number of potentially confounding variables: hand hygiene compliance remained more or less the same, and bed occupancy and antibiotic usage increased. It is impressive that a reduction in contamination was observed despite increases in bed occupancy and antibiotic consumption, which have been shown to increase the risk of HCAI. The team even evaluated whether the ambient mean temperature differed between the two periods (it did not).
Although the study was performed in a single centre and no randomisation was involved, it was extraordinarily well controlled for the impact of potentially confounding variables. This study illustrates the “halo” effect of chlorhexidine daily bathing in reducing environmental contamination. This reduction in environmental contamination is likely to be a contributing factor to the improvement in clinical outcomes associated with chlorhexidine daily bathing.
A study published in the Lancet Infectious Diseases provides further evidence that UV room decontamination reduces transmission in hospitals. The multicentre cluster-randomised study showed that introducing UV room decontamination for selected patient rooms resulted in a hospital-wide reduction in C. difficile and VRE acquisition compared with standard methods of decontamination.
This is a companion article to the BETR-D study that was published in the Lancet last year. This huge multicentre cluster-randomised study involved around 300,000 admissions to 9 hospitals over two years. The hospitals used a random sequence of terminal disinfection strategies for rooms of patients with selected target pathogens (C. difficile, MRSA, VRE, and Acinetobacter spp.). The disinfection strategies were:
- QAC disinfectant plus sodium hypochlorite for difficile (the reference method),
- QAC + UV plus sodium hypochlorite plus UV for difficile,
- Sodium hypochlorite + UV, and
- Sodium hypochlorite.
The hospital-wide rate of acquisition of the target pathogens was investigated as a combined rate and for individual pathogens.
Overall, the QAC + UV proved to be the most effective strategy, with a relative risk of acquisition for all pathogens combined of 0.89 and with an upper confidence interval that just touched 1 (see Figure). This means that this reduction for all pathogens combined was right on the borderline of what would be considered statistically significant. This was driven by a statistically significant reduction in the acquisition of VRE (relative risk 0.56, confidence interval 0.31 – 0.996; p=0.048) and C. difficile (0.89, 95% CI 0.80 – 0.99; p=0.031).
Figure 1: The relative risk of acquiring all target pathogens combined for the test methods compared with the reference method, which was QAC disinfectant for all pathogens plus sodium hypochlorite for C. difficile
These findings are curious in some ways. The original BETR-D study showed that patients coming into rooms disinfected using UV were less likely to acquire target pathogens than patients admitted to rooms disinfected using standard methods. Here, the question was whether improved terminal disinfection would have a hospital wide impact, and this was shown to be the case for VRE and C. difficile. This suggests that improving terminal disinfection not only improves patient outcomes for the next patient to occupy a single room, but has knock-on clinical benefits measurable across the entire hospital!
These findings strengthen the case for enhancing terminal disinfection strategies by adding automated room decontamination systems, such as UV.