Tackling contamination of the hospital environment by methicillin-resistant Staphylococcus aureus (MRSA): a comparison between conventional terminal cleaning and hydrogen peroxide vapour decontamination

The hospital environment can sometimes harbour methicillin-resistant Staphylococcus aureus (MRSA) but is not generally regarded as a major source of MRSA infection. We conducted a prospective study in surgical wards of a London teaching hospital affected by MRSA, and compared the effectiveness of standard cleaning with a new method of hydrogen peroxide vapour decontamination. MRSA contamination, measured by surface swabbing was compared before and after terminal cleaning that complied with UK national standards, or hydrogen peroxide vapour decontamination. All isolation rooms, ward bays and bathrooms tested were contaminated with MRSA and several antibiogram types were identified. MRSA was common in sites that might transfer organisms to the hands of staff and was isolated from areas and bed frames used by non-MRSA patients. Seventy-four percent of 359 swabs taken before cleaning yielded MRSA, 70% by direct plating. After cleaning, all areas remained contaminated, with 66% of 124 swabs yielding MRSA, 74% by direct plating. In contrast, after exposing six rooms to hydrogen peroxide vapour, only one of 85 (1.2%) swabs yielded MRSA, by enrichment culture only. The hospital environment can become extensively contaminated with MRSA that is not eliminated by standard cleaning methods. In contrast, hydrogen peroxide vapour decontamination is a highly effective method of eradicating MRSA from rooms, furniture and equipment. Further work is needed to determine the importance of environmental contamination with MRSA and the effect on hospital infection rates of effective decontamination.     

Gaseous and air decontamination technologies for Clostridium difficile in the healthcare environment

The recent data for hospital-acquired infections suggest that infection rates for meticillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile are beginning to decrease. However, while there is still pressure to maintain this trend, the resistance of C. difficile spores to standard detergents continues to present a problem for many UK hospitals trying to prevent its spread or control outbreaks. Alternative disinfection technologies such as gaseous decontamination are currently being marketed to the healthcare sector as an alternative/supplement to manual disinfection, and have been shown to be effective in reducing environmental contamination. When used correctly, they offer a complementary technology to manual cleaning that increases the probability of an effective reduction in viability and provides a comparatively uniform distribution of disinfectant. Three gaseous decontamination technologies are examined for their suitability in reducing environmental contamination with C. difficile: gaseous hydrogen peroxide, chlorine dioxide and ozone. Air decontamination and UV-based technologies are also briefly described. We conclude that while there is a role to play for these new technologies in the decontamination of ward surfaces contaminated with C. difficile, the requirement for both a preclean before use and the limited 'in vivo' evidence means that extensive field trials are necessary to determine their cost-effectiveness in a healthcare setting.     

Airborne hydrogen peroxide for disinfection of the hospital environment and infection control: a systematic review

We reviewed the effectiveness of airborne hydrogen peroxide as an environmental disinfectant and infection control measure in clinical settings. Systematic review identified ten studies as eligible for inclusion. Hydrogen peroxide was delivered in the form of vapour and dry mist in seven and three studies, respectively. Pathogens evaluated included meticillin-resistant Staphylococcus aureus (MRSA), Clostridium difficile and multiple bacterial types, in five, three, and two studies, respectively. Before the application of any cleaning intervention, 187/480 (39.0%; range: 18.9-81.0%) of all sampled environmental sites were found to be contaminated by the studied pathogens in nine studies that reported specific relevant data. After application of terminal cleaning and airborne hydrogen peroxide, 178/630 (28.3%; range: 11.9-66.1%) of the sampled sites in six studies and 15/682 (2.2%; range: 0-4.0%) of the sampled sites in ten studies, respectively, remained contaminated. Four studies evaluated the use of hydrogen peroxide vapour for infection control. This was associated with control of a nosocomial outbreak in two studies, eradication of persistent environmental contamination with MRSA and decrease in C. difficile infection in each of the remaining two studies.     

Rapid recontamination with MRSA of the environment of an intensive care unit after decontamination with hydrogen peroxide vapour

Meticillin-resistant Staphylococcus aureus (MRSA) persists in the hospital environment and conventional cleaning procedures do not necessarily eliminate contamination. A prospective study was conducted on an intensive care unit to establish the level of environmental contamination with MRSA, assess the effectiveness of hydrogen peroxide vapour (HPV) decontamination and determine the rate of environmental recontamination. MRSA was isolated from 11.2% of environmental sites in the three months preceding the use of HPV and epidemiological typing revealed that the types circulating within the environment were similar to those colonising patients. After patient discharge and terminal cleaning using conventional methods, MRSA was isolated from five sites (17.2%). After HPV decontamination but before the readmission of patients, MRSA was not isolated from the environment. Twenty-four hours after readmitting patients, including two colonized with MRSA, the organism was isolated from five sites. The strains were indistinguishable from a strain with which a patient was colonized but were not all confined to the immediate vicinity of the colonized patient. In the eight weeks after the use of HPV, the environment was sampled on a weekly basis and MRSA was isolated from 16.3% sites. Hydrogen peroxide vapour is effective in eliminating bacteria from the environment but the rapid rate of recontamination suggests that it is not an effective means of maintaining low levels of environmental contamination in an open-plan intensive care unit.     

Prospective evaluation of environmental contamination by Clostridium difficile in isolation side rooms.

We determined prospectively the frequency, persistence and molecular epidemiology of Clostridium difficile environmental contamination after detergent-based cleaning in side rooms used to isolate patients with C. difficile diarrhoea. Approximately one-quarter of all environmental sites in side rooms sampled over four-week periods were contaminated with C. difficile. The overall side room prevalence of environmental C. difficile declined from 35% initially, to 24% in week 2, 18% in week 3, and 16% in week 4. The bed frame was the most common site from which C. difficile was recovered, although the floor was the most contaminated site in terms of total numbers of colonies. C. difficile was recovered significantly more frequently from swabs plated directly on to C. difficile selective media containing lysozyme than from enrichment broth (P< 0.001), emphasizing the benefit of lysozyme supplementation. The great majority of C. difficile isolates (87% of all isolates, 84% of patient isolates) was indistinguishable from the UK epidemic strain (PCR ribotype 1). It thus could not be determined whether environmental contamination was a cause or a consequence of diarrhoea. Our findings highlight the need for improved approaches to hospital environmental hygiene, and call into question current UK guidelines that recommend detergent-based cleaning to remove environmental C. difficile. In particular, improved cleaning of frequently touched sites in the immediate bed space area is required.     

Efficacy of hospital cleaning agents and germicides against epidemic Clostridium difficile strains.

OBJECTIVE: To compare the effects of hospital cleaning agents and germicides on the survival of epidemic Clostridium difficile strains. METHODS: We compared the activity of and effects of exposure to 5 cleaning agents and/or germicides (3 containing chlorine, 1 containing only detergent, and 1 containing hydrogen peroxide) on vegetative and spore forms of epidemic and non-epidemic C. difficile strains (3 of each). We carried out in vitro exposure experiments using a human fecal emulsion to mimic conditions found in situ. RESULTS: Cleaning agent and germicide exposure experiments yielded very different results for C. difficile vegetative cells, compared with those for spores. Working-strength concentrations of all of the agents inhibited the growth of C. difficile in culture. However, when used at recommended working concentrations, only chlorine-based germicides were able to inactivate C. difficile spores. C. difficile epidemic strains had a greater sporulation rate than nonepidemic strains. The mean sporulation rate, expressed as the proportion of a cell population that is in spore form, was 13% for all strains not exposed to any cleaning agent or germicide, and it was significantly increased by exposure to cleaning agents or germicides containing detergent alone (34%), a combination of detergent and hypochlorite (24%), or hydrogen peroxide (33%). By contrast, the mean sporulation rate did not change substantially after exposure to germicides containing either a combination of detergent and dichloroisocyanurate (9%) or dichloroisocyanurate alone (15%). CONCLUSIONS: These results highlight differences in the activity of cleaning agents and germicides against C. difficile spores and the potential for some of these products to promote sporulation.     

Evaluation of the biological efficacy of hydrogen peroxide vapour decontamination in wards of an Australian hospital

This study assessed the efficacy of a 'dry' hydrogen peroxide vapour decontamination in an Australian hospital via a two-armed study. The in?vivo arm examined the baseline bacterial counts in high-touch zones within wards and evaluated the efficacy of cleaning with a neutral detergent followed by either hydrogen peroxide vapour decontamination, or a manual terminal clean with bleach or Det-Sol 500. The in?vitro arm examined the efficacy of hydrogen peroxide vapour decontamination on a variety of different surfaces commonly found in the wards of an Australian hospital, deliberately seeded with a known concentration of vancomycin-resistant enterococci (VRE). All bacterial counts were evaluated by a protocol of contact plate method. In the in?vivo arm, 33.3% of the high-touch areas assessed had aerobic bacterial count below the detection limit (i.e. no bacteria recoverable) post hydrogen peroxide decontamination, and in all circumstances the highest microbial density was ≤3?cfu/cm(2), while in the in?vitro arm there was at least a reduction in bacterial load by a factor of 10 at all surfaces investigated. These results showed that dry hydrogen peroxide vapour room decontamination is highly effective on a range of surfaces, although the cleanliness data obtained by these methods cannot be easily compared among the different surfaces as recovery of organisms is affected by the nature of the surface.     

Molecular epidemiology of endemic Clostridium difficile infection

This is the first study to provide a comprehensive insight into the molecular epidemiology of endemic Clostridium difficile and particularly that associated with a recently recognized epidemic strain. We DNA fingerprinted all C. difficile isolates from the stools of patients with symptomatic antibiotic-associated diarrhoea and from repeated samples of the inanimate ward environment on two elderly medicine hospital wards over a 22-month period. Notably, C. difficile was not recoverable from either ward immediately before opening, but was found on both wards within 1-3 weeks of opening, and the level of environmental contamination rose markedly during the first 6 months of the study period. C. difficile infection (CDI) incidence data correlated significantly with the prevalence of environmental C. difficile on ward B (r = 0.76, P < 0.05) but not on ward A (r = 0.26, P > 0.05). We found that RAPD and RS-PCR typing had similar discriminatory power, although, despite fingerprinting over 200 C. difficile isolates, we identified only six distinct types. Only two distinct C. difficile strains were identified as causing both patient infection and ward contamination. Attempts to determine whether infected patients or contaminated environments are the prime source for cross-infection by C. difficile had limited success, as over 90% of C. difficile isolates were the UK epidemic clone. However, a non-epidemic strain caused a cluster of six cases of CDI, but was only isolated from the environment after the sixth patient became symptomatic. The initial absence of this strain from the environment implies patient-to-patient and/or staff-to-patient spread. In general, routine cleaning with detergent was unsuccessful at removing C. difficile from the environment. Understanding the epidemiology and virulence of prevalent strains is important if CDI is to be successfully controlled.     

Risk of bioaerosol contamination with Aspergillus species before and after cleaning in rooms filtered with high-efficiency particulate air filters that house patients with hematologic malignancy.

OBJECTIVE: To examine the impact of cleaning and directional airflow on environmental contamination with Aspergillus species in hospital rooms filtered with high-efficiency particulate air (HEPA) filters that house patients with hematologic malignancy. DESIGN: Detailed environmental assessment. SETTING: A 475-bed tertiary cancer center in the southern United States. METHODS: From April to October 2004, 1,258 surface samples and 627 bioaerosol samples were obtained from 74 HEPA-filtered rooms (in addition, 88 outdoor bioaerosol samples were obtained). Samples were collected from rooms cleaned within 1 hour after patient discharge and from rooms before cleaning. Positive and negative airflows were evaluated using air-current tubes at entrances to patient rooms. RESULTS: Of 1,258 surface samples, 3.3% were positive for Aspergillus species. Univariate analysis showed no relationship between cleaning status and occurrence of Aspergillus species. Of 627 bioaerosol samples, 7.3% were positive for Aspergillus species. Multiple logistic analysis revealed independently significant associations with detection of Aspergillus species. Cleaned rooms positive for Aspergillus species had a higher geometric mean density of colonies than that of rooms sampled before cleaning (18.9 vs 5.5 colony-forming units [cfu] per cubic meter; P=.0047). Rooms with positive airflow had a detection rate for bioaerosol samples equivalent to that of rooms with negative airflow (7.3% vs 7.8%; P=.8). There was no significant difference in the density of Aspergillus species between rooms with negative airflow and rooms with positive airflow (12.5 vs 8.4 cfu/m(3); P=.33). CONCLUSIONS: Concentration of bioaerosol contamination with Aspergillus species was increased in rooms sampled 1 hour after cleaning compared with rooms sampled before cleaning, suggesting a possible correlation between re-entrained bioaerosols (ie, those suspended by activity in the room) after cleaning and the risk of nosocomial invasive aspergillosis.     

Decontamination of rooms, medical equipment and ambulances using an aerosol of hydrogen peroxide disinfectant

A programmable device (Sterinis, Gloster Sante Europe) providing a dry fume of 5% hydrogen peroxide (H(2)O(2)) disinfectant was tested for decontamination of rooms, ambulances and different types of medical equipment. Pre-set concentrations were used according to the volumes of the rooms and garages. Three cycles were performed with increasing contact times. Repetitive experiments were performed using Bacillus atrophaeus (formerly Bacillus subtilis) Raven 1162282 spores to control the effect of decontamination; after a sampling plan, spore strips were placed in various positions in rooms, ambulances, and inside and outside the items of medical equipment. Decontamination was effective in 87% of 146 spore tests in closed test rooms and in 100% of 48 tests in a surgical department when using three cycles. One or two cycles had no effect. The sporicidal effect on internal parts of the medical equipment was only 62.3% (220 tests). When the devices were run and ventilated during decontamination, 100% (57/57) of spore strips placed inside were decontaminated. In the ambulances, the penetration of H(2)O(2) into equipment, devices, glove boxes, under mattresses, and the drivers' cabins was 100% (60/60 tests) when using three cycles, but was less effective when using one or two cycles. In conclusion, an H(2)O(2) dry fumigation system, run in three cycles, seemed to have a good sporicidal effect when used in rooms, ambulances, and external and internal parts of ventilated equipment. Further studies need to be performed concerning concentration, contact time and the number of cycles of H(2)O(2). This is especially important for inner parts of medical equipment that cannot be ventilated during the decontamination process.     

Comparison of the effect of detergent versus hypochlorite cleaning on environmental contamination and incidence of Clostridium difficile infection

To determine how best to decontaminate the hospital environment of Clostridium difficile, we carried out a cross-over study on two elderly medicine wards to determine whether cleaning with a hypochlorite disinfectant was better than using neutral detergent in reducing the incidence of C. difficile infection (CDI). We examined 1128 environmental samples in two years, 35% of which grew C. difficile. There was a significant decrease of CDI incidence on ward X, from 8.9 to 5.3 cases per 100 admissions (P<0.05) using hypochlorite, but there was no significant effect on ward Y. On ward X the incidence of CDI was significantly associated with the proportion of culture-positive environmental sites (P<0.05). On ward Y the only significant correlation between CDI and C. difficile culture-positive environmental sites was in patient side-rooms (r=0.41, P<0.05). The total daily defined doses of cefotaxime, cephradine and aminopenicillins were similar throughout the trial. These results provide some evidence that use of hypochlorite for environmental cleaning may significantly reduce incidence of CDI, but emphasize the potential for confounding factors.     

Environmental reservoirs of methicillin-resistant Staphylococcus aureus in isolation rooms: correlation with patient isolates and implications for hospital hygiene

Strategies to control and prevent the spread of methicillin-resistant Staphylococcus aureus (MRSA) include early identification of positive patients through screening, patient isolation, hand hygiene, nasal and skin decontamination, and the adequate cleaning and decontamination of clinical areas. However, many national and other guidelines provide few details on environmental decontamination regimens, partly because the role of the environment in the spread of MRSA is not well documented. We prospectively studied the environment of the isolation rooms of 25 MRSA patients for up to four weeks, sampling horizontal surfaces and the air using settle plates as well as an air sampler, while continuing regular daily cleaning according to the hospital protocol. We then typed 20 patient isolates and the corresponding environmental isolates (N=35) to assess the similarity of strains. A high proportion of samples were positive for MRSA; 269/502 (53.6%) surface samples, 70/250 (28%) air samples and 102/251 (40.6%) settle plates. Over half of the surface samples taken from the beds and the mattresses were positive for MRSA. Identical or closely related isolates were recovered from the patient and their environment in 14 (70%) patients, suggesting possible environmental contamination of the isolation rooms, possibly contributing to endemic MRSA. More effective and rigorous use of current approaches to cleaning and decontamination is required as well as consideration of newer technologies to eradicate MRSA and other hospital-acquired pathogens.     

Value of lysozyme agar incorporation and alkaline thioglycollate exposure for the environmental recovery of Clostridium difficile

Clostridium difficile is an increasingly prevalent nosocomial pathogen. Environmental contamination by spores is believed to be a major factor propagating the spread of C. difficile. Various approaches including the use of bile salts have been described to enhance the recovery of C. difficile from clinical and environmental specimens. We found that lysozyme (5 mg/L) incorporated into a selective medium containing bile salts significantly increased the recovery of C. difficile from swabs of 197 environmental sites (11% versus 24% samples positive, P< 0.01). Furthermore, in a separate series of experiments additional use of cooked meat broth enrichment significantly enhanced the recovery of C. difficile (35% versus 45%, P = 0.009). Conversely, we found that pre-exposure to alkaline thioglycollate did not improve the yield of C. difficile. Lysozyme incorporation markedly increases the recovery of C. difficile from environmental samples probably by stimulation of spore germination. Our findings suggest that previous attempts to determine the level of environmental C. difficile contamination have markedly underestimated the true prevalence of this pathogen.     

Relationship between environmental fungal contamination and the incidence of invasive aspergillosis in haematology patients.

Invasive aspergillosis (IA) is a major opportunistic infection in haematology patients. Spore inhalation is the usual route of Aspergillus infection, suggesting a determining role of environmental contamination by spores in the epidemiology of IA. We prospectively examined the relationship between environmental contamination by Aspergillus and other fungal species and the incidence of invasive nosocomial aspergillosis (INA) in a bone marrow transplantation unit and two haematology wards. During a four-year period, levels of air and surface fungal contamination were determined bi-monthly in patients' rooms (some equipped with HEPA filters and LAF systems), and various common sites in each ward (corridors, nursing stations, etc.). Results were compared to the incidence of INA. A total of 3100 air and 9800 surface samples were collected, and 79 cases of IA were diagnosed, of which 64 were probably or possibly INA. Patterns of fungal contamination were comparable in the three wards, with a gradient ranging from high levels in common sites to a virtual absence in rooms equipped with HEPA filters and LAF systems. Using a regression model, a significant relationship was found between the incidence of INA and the degree of fungal contamination of air and surfaces in conventional patient rooms (not equipped with HEPA) and common sites. This study shows that in a non-epidemic setting, there is a significant relationship between environmental fungal contamination in haematology wards and the incidence of INA. Our findings underline the importance of environmental surveillance and strict application of preventive measures.     

Activity in vitro of hydrogen peroxide vapour against Clostridium difficile spores

Clostridium difficile spores are shed in high numbers by infected patients and are resistant to desiccation and some disinfectants. We explored the in?vitro activity of hydrogen peroxide vapour (HPV) against several strains of C.?difficile spores using a spore-carrier test. Spores were dried on polyvinyl chloride or laminate carriers at mean concentrations of 4.7-6.9 log(10) spores/carrier, which were then decontaminated using HPV. C.?difficile was completely eradicated from the exposed carriers regardless of the C.?difficile strain or surface used. HPV can be considered for the eradication of C.?difficile spores from the hospital environment.     

Hydrogen peroxide vapour for decontaminating air-conditioning ducts and rooms of an emergency complex in northern India: time to move on

Overcrowding and patient overload in emergency services areas often mean that inadequate attention is paid to thorough cleaning, disinfection of rooms and air-conditioning ducts, which would require closing the area concerned. Over a period of time, this leads to accumulation of lint, fibre, dust and fungal growth. This study assessed the effectiveness of hydrogen peroxide fog to decontaminate the air-conditioning ducts as well as for room disinfection without having to close down the area. The Postgraduate Institute of Medical Education and Research emergency complex, Chandigarh, is distributed over three floors housing nine air-handling units (AHUs) and seven wards. The work was carried out over a period of seven days and involved cleaning of air-conditioning ducts and wards, cleaning and disinfection of fittings and furniture, vacuuming and fogging of AHU, ducts and room air. Fogging was done with 20% Ecoshield fog, a complex formulation of stabilised hydrogen peroxide 11% w/v with 0.015% w/v silver nitrate. Pre- and post-fogging samples were taken for microbiological culture, and air samples were also collected. Hydrogen peroxide fogging was highly effective for disinfection of room air, furniture and other articles. It decontaminated the air-conditioning ducts effectively, was rapid and cheaper than formalin, and no adverse effects were noted. There was minimum disturbance to the patients and the treated areas were ready to be populated again after 5-6h. Hydrogen peroxide has the advantage of being safer, less irritating, and has shorter cycle times compared with formalin fumigation which is more commonly practised in India.     

Environmental investigations and molecular typing of Aspergillus flavus during an outbreak of postoperative infections

After an outbreak of sternal surgical-site infections (SSSI) with Aspergillus flavus following cardiac surgery, a mycological survey of air and surfaces (41 and 149 samples, respectively) was performed throughout the surgical ward (SW) and in other areas of the hospital. Results showed massive contamination by A. flavus: more than 100 cfu per contact plate were frequently observed in some areas of the SW. The distribution of the A. flavus spores in the building, and especially in the SW, enabled the location of a possible source within the non-medical part of the SW, but the true source could not be identified. Four other surveys were made to follow up the decontamination process; the contamination level did not fall rapidly, needing repetitive cleaning operations. Strains from patients and from the hospital environment selected all over the SW were typed by random amplification of polymorphic DNA (RAPD), using two different primers (ERIC-1, BG-2). All these strains showed the same genotype, proving the clonal single-source of the environmental contamination and the intra-operative acquisition of A. flavus in the SSSI outbreak.     

Lack of enhanced effect of a chlorine dioxide-based cleaning regimen on environmental contamination with Clostridium difficile spores

Spores of Clostridium difficile may play a significant role in transmission of disease within the healthcare environment and are resistant to a variety of detergents and cleaning fluids. A range of environmental cleaning agents has recently become available, many of which claim to be sporicidal. We investigated the effect of changing to a chlorine dioxide-based cleaning regimen on C.?difficile environmental contamination and patient infection rates. The prevalence of environmental contamination was unaffected with a rate of 8% (9/120) before and 8% (17/212) following the change. Rates of patient infection were also unchanged during these periods.     

Contamination of room door handles by methicillin-sensitive/methicillin-resistant Staphylococcus aureus

We investigated the contamination of room door handles by Staphylococcus aureus in wards of a university hospital. Door handles in 53 (27.0%) of 196 rooms were contaminated by methicillin-sensitive Staphylococcus aureus (MSSA) and/or methicillin-resistant Staphylococcus aureus (MRSA); MSSA was detected on door handles of 41 rooms (20.9%), MRSA on door handles of 17 rooms (8.7%), and MSSA and MRSA on the same door handles of five rooms (2.6%). The density of MSSA contamination was 1-2.6x10(4) colony forming units (cfu)/door handle, and that of MRSA was 1-6.0x10(3) cfu/door handle. The MRSA contamination rate on door handles of rooms with patients with MRSA was 19.0% (4/21 rooms) while that on door handles of rooms with patients without MRSA was 7.4% (13/175); the difference was not significant. These results suggest extensive contamination of MSSA and MRSA in the hospital environment.     

Assessing the biological efficacy and rate of recontamination following hydrogen peroxide vapour decontamination

The inanimate hospital environment can become contaminated with nosocomial pathogens. Hydrogen peroxide vapour (HPV) decontamination has proven effective for the eradication of persistent environmental contamination. We investigated the extent of meticillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and gentamicin-resistant Gram-negative rod (GNR) contamination in a ward side-room occupied by a patient with a history of MRSA, VRE and GNR infection and colonisation and investigated the impact of HPV decontamination. Fifteen standardised sites in the room were sampled using a selective broth enrichment protocol to culture MRSA, VRE and GNR. Sampling was performed before cleaning, after cleaning, after HPV decontamination and at intervals over the subsequent 19 days on two separate occasions. Environmental contamination was identified before cleaning on 60, 30 and 6.7% of sites for MRSA, GNR and VRE, respectively, and 40, 10 and 6.7% of sites after cleaning. Only one site (3.3%) was contaminated with MRSA after HPV decontamination. No recontamination with VRE was identified and no recontamination with MRSA and GNR was identified during the two days following HPV decontamination. Substantial recontamination was identified approximately one week after HPV decontamination towards post-cleaning levels for GNR and towards pre-cleaning levels for MRSA. HPV is more effective than standard terminal cleaning for the eradication of nosocomial pathogens. Recontamination was not immediate for MRSA and GNR but contamination returned within a week in a room occupied by a patient colonised with MRSA and GNR. This finding has important implications for the optimal deployment of HPV decontamination in hospitals.