Blazing a vapour trail
Hydrogen peroxide vapour provides a powerful new weapon for hospitals in the infection control armoury, argues Jon Otter, a lead microbiologist with Bioquell
Approximately 1 in 10 hospitalised patients will acquire a Healthcare-Associated Infection (HCAI). According to 1999 figures, HCAIs complicate and extend the patient’s hospital stay, are responsible for the death of at least 5,000 people in the UK and cost the NHS approximately £1bn per annum.1 These costs of HCAIs are almost certainly underestimated and do not include intangible costs, such as suffering, and exclude the costs of litigation, which are significant and increasing.
The problems caused by HCAIs are compounded by several factors. Advances in medical care have resulted in a higher proportion of patients being treated with weakened immune systems, which makes them more susceptible to infection. New organisms have emerged as a cause of infection, and old organisms have adapted to cause more severe infection or affect new patient populations. The persistent use, overuse and misuse of antibiotics since their introduction in the 1940s has bred antibiotic-resistant “Super-bugs”, which are more difficult to treat.
The reliance on antibiotics to treat HCAI has served to undermine simple infection control principles established in the pre-antibiotic era, principally that an emphasis on hygiene (comprising hand washing and environmental cleanliness) is crucial for controlling the spread of the micro-organisms responsible for HCAI, which are technically termed nosocomial pathogens. Currently there are no new classes of antibiotics in the pipeline. The fact that antibiotics often rapidly become resistant to bacteria – with, for example, resistance to methicillin being reported within about a year of its launch in the UK – means that the financial returns available to the pharmaceutical companies are relatively poor and hence there is little incentive to fund the substantial costs of developing new antibiotics (only to see them become resistant to bacteria).
Despite several local, national and global initiatives, the rate of antibiotic resistance in nosocomial pathogens continues to rise. This can be seen clearly with methicillin-resistant Staphylococcus aureus (MRSA): the prevalence of MRSA in blood isolates taken from patients in hospitals in the UK rose from 3% in 1992 to 40% in 2004.2
MRSA is the infamous hospital superbug, but other micro-organisms (usually bacteria) are common causes of HCAI. For example, we are in the midst of a pandemic (or global epidemic) of a new strain of Clostridium difficile, called the 027 strain, which causes diarrhoea and can result in severe bowel inflammation and even death.3 Acinetobacter spp., which is a common cause of infection on Intensive Care Units (ICU), is another cause for concern. Although the infections caused by Acinetobacter spp. are typically less severe than those caused by other nosocomial pathogens, such as MRSA, the levels of resistance in Acinetobacter spp. are extremely high and untreatable strains of Acinetobacter spp. are a very real possibility.4 The list does not end there: Norovirus causes diarrhoea and vomiting amongst patient and staff and is highly transmissible; and Vancomycin-resistant enterococci (VRE), also known as Glycopeptide-resistant enterococci (GRE), is another common cause of HCAI with increasing rates of resistance.
The increasing rates of antibiotic resistance mean that we are now faced with the real but frightening possibility of a return to the pre-antibiotic era, with palliative care as the only therapeutic option.
Hospital contamination
Contaminated hands of healthcare workers are the most common route of transmission for nosocomial pathogens.5 However, the hands of healthcare workers can become contaminated indirectly through contact with contaminated environmental surfaces, even after cleaning;6 hence environmental surfaces can be reservoirs for indirect transmission. Many nosocomial pathogens including MRSA, C. difficile, Acinetobacter spp., Norovirus and VRE contaminate inanimate surfaces and objects in the hospital environment.7 Nevertheless, there is controversy in the scientific literature surrounding the exact contribution of environmental contamination to the transmission of nosocomial pathogens.
There are a number of reasons why the importance of environmental contamination in hospitals has been overlooked historically. First, the advent of antibiotics promoted a move towards a reliance on the treatment rather than prevention of infectious diseases in hospitals, with a concurrent relaxation of simple hygienic measures.8 Second, it was thought that vegetative (non-spore forming) bacteria died quickly when dried onto surfaces and did not survive for long outside the body.9 Third, studies in the 1970s and 1980s provided evidence that environmental contamination was not a key risk factor for the transmission of nosocomial pathogens.10 However, the latest scientific research and opinion has promoted a re-assessment of the role of environmental contamina-tion in the transmission of nosocomial pathogens. Key studies have demonstrated that nosocomial pathogens, including MRSA, can survive for months and even years on dry surfaces and that a focus on environmental decontamination can reduce the incidence of HCAI.7,8
Therefore, aside from the intuitive fact that most patients would prefer to be cared for in a room or bed-space free of potentially dangerous nosocomial pathogens, there is accumulating scientific evidence that a contaminated environment is an important reservoir for transmission of nosocomial pathogens.
Bioquell has developed a novel and patent-protected range of hydrogen peroxide vapour (HPV) bio-decontamination systems for the deactivation of micro-organisms, including bacteria, viruses and fungi in the healthcare, pharmaceutical, biotechnology and food industries. HPV is used increasingly for the bio-decontamination of cleanrooms and research facilities in the pharmaceutical industry.
The company initiated a research programme over five years ago to investigate the potential application of its Clarus HPV technology for the deactivation of environmentally associated nosocomial pathogens. The programme has yielded encouraging results11 and the HPV technology has been deployed successfully in hospitals throughout the world.
The HPV decontamination system used in hospitals consists of four portable modules: the Clarus R HPV generator, the Clarus R2 aeration unit, an instrumentation module and a control computer (see figure 1). The Clarus R is placed within the room and vaporises 30% w/w liquid hydrogen peroxide. The resulting vapour is delivered via a dual axis distribution system that ensures high velocity and even distribution throughout the room. The HPV concentration, temperature and relative humidity within the room are measured by the instrumentation module and monitored by a control computer situated outside the room. When decontamination is complete, Clarus R2 aeration units inside the room catalytically convert the HPV into water vapour and oxygen so the process leaves no harmful residues. Each new cycle is verified by the use of Tyvek-pouched 6-log Geobacillus stearothermophilus biological indicators; the same type used to verify the efficacy of autoclaves, which provides assurance of the biological efficacy of the process.
HPV bio-decontamination is a micro-condensation process that produces a higher concentration in the condensate than the source aqueous solution.12 This results in rapid and reliable kill of micro-organisms within the enclosure being treated. Because micro-organisms act as nuclei for condensation, only very small amounts of condensation are required, normally averaging no more than a few microns in thickness.
Although many liquid disinfectants exist and have an important role in the disinfection of hospitals, the hospital environment presents several unique challenges to effective decontamination. Modern healthcare utilises sensitive electronic devices to provide state-of-the-art healthcare. This medical equipment often has an intricate design and it is usually not possible to ensure an adequate contact time to achieve effective decontamination using a liquid disinfectant. Also, certain chemical disinfectants, such as sodium hypochlorite (bleach), may not be suitable for the disinfection of sensitive electronics due to significant material compatibility issues. A vapour-phase method, such as HPV, which is non-corrosive, provides a useful option for the effective decontamination of the intricate surfaces and interior of medical equipment common in modern healthcare facilities.
Through collaboration with hospitals and academic institutions, Bioquell has produced strong scientific evidence supporting the use of its technology for the control of nosocomial pathogens in hospitals.
The pilot deployment at St. Thomas’ Hospital, London in 2004 demonstrated that the technology is able to eradicate MRSA environmental contamination, which was shown to persist despite terminal cleaning (figure 2).11 Based on this research, in December 2004, the UK Department of Health’s Rapid Review Panel identified Bioquell’s HPV technology as one of three technologies assessed with potential value in the fight against MRSA. The RRP stated that “The basic research and development, validation and in use evaluations have shown potential benefits, which should be available to NHS bodies, to include hydrogen peroxide vapour into their cleaning or infection control protocols.”
Since this time, several other publications have highlighted the efficacy of HPV decontamination for the control of outbreaks in hospitals. For example, one publication reported the use of HPV decontamination for the control of an MRSA outbreak on a surgical ward (see case study 1)13 and another for Serratia marcescens on a Neonatal Intensive Care Unit (NICU) (case study 2).14
Latest research
Bioquell initiated a collaborative research project with a Yale University-affiliated hospital on the East Coast of the USA and the Centers for Disease Control and Prevention (CDC). The hospital had experienced an outbreak of the pandemic 027 C. difficile strain, which persisted despite enhanced infection control measures. Bioquell’s HPV technology was implemented across the hospital and resulted in a statistically significant 53% reduction in hospital-wide rate of C. difficile-associated disease (CDAD) since the pandemic strain was first noted in the hospital.15 This is the first study to show that the hospital-wide HCAI rate can be reduced through regular HPV decontamination of the hospital environment.
In addition to the peer-reviewed scientific studies discussed above, Bioquell has deployed its technology in many other hospitals to control nosocomial pathogens including Acinetobacter sp., C. difficile, VRE and Norovirus.
HCAI imposes a significant and increasing burden on healthcare providers worldwide. Although MRSA is one of the most common and important nosocomial pathogens, other nosocomial pathogens such as Acinetobacter and C. difficile are becoming increasingly prevalent.
Although the exact contribution of environmental contamination to nosocomial cross infection remains controversial, there is compelling evidence that contaminated hospital surfaces provide a reservoir for cross transmission. HPV decontamination has been shown to eradicate nosocomial pathogens from hospitals surfaces and, in doing so, break the circle of transmission and allow outbreaks to be brought under control. The latest research has shown that routine HPV decontamination can reduce the hospital-wide rate of HCAI.
HPV technology can now be considered a viable option for the environmental control of nosocomial pathogens in hospitals, especially during outbreaks.
