There is a general feeling that being antibiotic resistant imposes a considerable fitness cost for bacteria - and the more resistant, the less fit the bacterium becomes. Whilst this is no-doubt true to some degree, a recent study from Brazil shows that MRSA, MSSA and vancomycin-intermediate S. aureus (VISA) have very similar survival properties on dry surfaces.
One strain of MRSA, MSSA and VISA were dried onto various surfaces and survived for a similar length of time. In general, S. aureus survive better on non-porous surfaces than on porous surfaces - and VISA 'out-survived' the MRSA and MSSA strain on the non-porous surfaces. However, VISA didn't do so well on the porous surfaces, surviving for less time than MRSA and MSSA. Previous studies have suggested that VISA are better at forming biofilms than other S. aureus. This was tested, but did not seem to be the case ' the MRSA strain seemed to be the most effective biofilms producer.
However, since only one strain of each type was tested, it is difficult to be certain of any comparisons. Previous work has illustrated considerable strain variation in the survival properties of S. aureus, so it's a shame that more strains were not included for each group. Nonetheless, the study shows that even highly antibiotic-resistant S. aureus retains the ability to produce biofilm and survive on dry surfaces for extended periods.
There is a general view that bleach is a well-proven intervention to prevent the transmission of pathogens associated with HCAI, especially C. difficile. However, a systematic review from some Spanish researchers highlights the limitations of the evidence base. Importantly, the review highlighted the limitations of bleach in dealing with dirty surfaces, which inactivate the bleach to a surprising degree, and surface-dried viruses, which exhibit considerable reduced susceptibility to bleach. Other disinfectants are also likely to suffer reduced susceptibility when dealing with dirty surfaces, and surface attached microbes, but it does seem that bleach is particularly sensitive to inactivation by dirty surfaces.
The review identified only four studies that evaluated the impact of introducing bleach as a single intervention to prevent cross-transmission (Orenstein, Hacek, McMullen, and Wilcox). Bleach was commonly implemented in tandem with other interventions, but these were not eligible for inclusion because it is not possible to determine the relative contribution of each. It was a surprise not to see the Mayfield study included in this review; it must have slipped through the inclusion criteria somehow. Also noteworthy that one of these studies (Wilcox) showed that bleach was ineffective when the pre-planned cross-over occurred, suggesting that other factors were also involved in the rate of C. difficile infection. The plan was to perform a meta-analysis of the available studies, but this was not possible due to the variable structure and quality of the studies - not least the concentration of bleach used.
This review certainly did not conclude that bleach is ineffective and presented some useful data that implementing bleach can help to reduce the transmission of hospital pathogens. However, the evidence-base for using bleach is not as strong as you may think, and further studies are required to explore the clinical impact of bleach and other options for hospital surface disinfection.
Another abstract published at the recent ID Week meeting (on page 13)* in the USA has added to the burgeoning collection of studies that indicate that the routine use of UV-C disinfection of clinical areas carries a clinical benefit. The paper from David Pegues and colleagues from the University of Pennsylvania examined the effect of UV-C as part of terminal disinfection on inpatient units that had a persistently high rate of Clostridium difficile infection (CDI) despite multiple interventions.
The study was carried out over a one-year period in three haematology/oncology units totalling 75 mostly single-bedded rooms. All rooms housing patients with either CDI or who were on contact precautions were disinfected using a UVDI machine that is marketed in the UK by Gama Healthcare as the UV-360. Two machines were used over the year and a total of 542 rooms were disinfected using this method (21% of all discharges). Impressively, the use of this machine for two 8-minute cycles in each room did not necessitate any increase in staffing requirement- for the adoption of this measure.
Analysis of data from the intervention year when compared with the previous year demonstrated a significant association between the use of the UV-C and a decline in CDI on the study units, whereas rates increased on the non-study units. Hopefully the authors of this abstract will submit a full paper to a peer-reviewed journal so that fuller information about the conduct of the study can be shared, however the conclusions of the authors are unequivocal; The targeted use of UV-C resulted in a substantial reduction in CDI with no adverse effect on room turnaround. Read it the paper online here
Infection Prevention 2015 (the annual conference of the Infection Prevention Society) has just wrapped up in Liverpool so we thought we'd share some of the key updates around environmental science.
Martin Kiernan gave a great lecture on the importance of the contaminated environment in the transmission of multidrug-resistant Gram-negative rods. Historically, the general view has been that Gram-negative bacteria don't survive well on surfaces, but recent data has suggested that this is often not the case. The non-fermenters (especially A. baumannii) survive well on surfaces, with survival times measured in months. Even the Enterobacteriaceae including highly resistant CPE (especially K. pneumoniae) can also exhibit surface survival times measured in months. Indeed, Professors Peter Hawkey and Ed Septimus also gave lectures highlighting the potential role of surface contamination in the transmission of resistant Gram-negative bacteria. Martin also discussed the relative recent finding that biofilms on dry hospital surfaces probably play an important and previously unrecognised role in facilitating the survival of Gram-negative bacteria; indeed, one study found that biofilm-producing A. baumannii showed longer surface survival times than non-biofilm-producing strains. There is evidence that even thorough, repeated bleach disinfection does not eliminate reservoirs of A. baumannii, so perhaps it's no surprise that admission to a room previously occupied by a patient with A. baumannii is a risk factor for acquisition! So what can be done to address surface contamination with Gram-negative bacteria?
- Using objective measures (such as fluorescent markers) to improve the cleaning process can help.
- The use of chlorhexidine to reduce shedding of bacteria from patients can reduce environmental contamination, and a recent study suggests that it can reduce the transmission of carbapenem-resistant A. baumannii.
- Automated room decontamination methods may play a role.
- And we need to develop a new generation of disinfectants with biofilms in mind!
All of the abstracts from the conference are published in an open access download from the Journal of Infection Prevention.
- A poster from the Royal Free (Abstract ID: 3781) evaluated the staff acceptability of Clinell's Universal and Sporicidal wipes to replace the previous protocol of chlorine solution diluted daily in buckets. Of the 100 staff surveyed, more than 90% agreed that the wipes were easier to access, more visible, easier to use, appeared effective, and would reduce the risk of dilution errors. As you would expect, the ease of use associated with wipes compared with a conventional "bucket method" was the most striking outcome of the survey.
- A poster from UCLH (Abstract ID: 3764) found that a fairly shocking 35% of surfaces in the near patient environment were contaminated with C. difficile after terminal disinfection with a sporicidal agent! Ribotyping and whole genome sequencing were used to investigate the relationship between environmental and patient isolates, and identified at least one case of environmental cross-transmission.
- As we all move towards mobile communication devices in our personal and professional lives, the tricky question about how and when to disinfect them is posed. A poster from Qatar (Abstract ID: 3772) evaluated a number of different methods for disinfecting an iPad experimentally contaminated with S. aureus. Brief exposure to UV light was the most effective method, achieving a 3-4 log reduction with a 60 second exposure.
- A study of a UVC room disinfection device from Royal Wolverhampton NHS Trust (Abstract ID: 3776) showed a statistically significant reduction of bacterial contamination compared with conventional manual cleaning, in line with other studies.
- Important research from PHE (Abstract ID: 3824) demonstrates that a number of commercial disinfectants are ineffective against some Gram-negative bacteria at their in-use concentration (see this review for more details here). Furthermore, Gram-negative bacteria tested in biofilms rather than planktonic cultures were even less susceptible to disinfectants. Finally, exposure to sub-lethal doses of some biocides resulted in further reduced susceptibility and antibiotic cross-resistance. This early-phase laboratory research raises some interesting questions and demonstrates the challenges that resistant Gram-negative bacteria pose to disinfection.
Thanks to the IPS for another great conference!