Aqueous oxygen peroxide treatment of VLUs in a primary care-based randomised, double-blind, placebo-controlled trial.

OBJECTIVE: To evaluate a novel aqueous oxygen peroxide (AOP) wound therapy (BioxyQuell) in a multi-centre, primary care-based, randomised, double-blind, placebo-controlled, parallel-group trial, monitoring long-term healing outcomes over 12 months. METHOD: Sixty-one patients with chronic, stable venous leg ulceration were treated with either AOP solution or sterile water placebo applied as a lavage over 2 weeks. The patients' wounds were dressed weekly and assessed fortnightly over the following 6 weeks. Patients who completed the initial 8-week trial were invited into a 10-month follow-up trial. The primary endpoints of the study were wound healing at 8 weeks, 12 weeks, 6 months and 12 months, and wound size reduction during the treatment phase. Secondary endpoints were reductions in wound bioburden and pain. RESULTS: Patients treated with AOP were more likely to heal at 6 months (p=0.014) and 12 months (p=0.006), but not at 8 weeks (p=0.979) or 12 weeks (p=0.263). Patients treated with AOP had greater wound area reduction (p=0.015), reductions in pain measured on a 100-point scale (p=0.001) and wound bioburden reduction (p=0.005) during the treatment phase. CONCLUSION: The addition of AOP treatment provides substantial benefits to patients with chronic venous leg ulceration compared with current best practice.

Assessing the stability and sporicidal efficacy of oxidizing disinfectants.

BACKGROUND: The role of the healthcare environment in the transmission of clinical pathogens is well established. EN 17126:2018 was developed to address the need for regulated sporicidal product testing and includes a realistic medical soil to enable validation of products that claim combined cleaning and disinfection efficacy. AIM: To investigate the chemical stability and sporicidal efficacy of oxidizing disinfectant products in the presence of simulated clean and medical dirty conditions. METHODS: Disinfectant stability and sporicidal efficacy were evaluated in like-for-like ratios of soil:product. Disinfectants were exposed to simulated test soils and free chlorine, chlorine dioxide or peracetic acid concentrations were measured using standard colorimetric methods. Efficacy of disinfectants against C. difficile R027 endospores was assessed as per EN 17126:2018. Comparisons of performance between clean and medical dirty conditions were performed using one-way analysis of variance. Correlation analysis was performed using Pearson product-moment correlation. FINDINGS: Performance of chlorine-releasing agents (sodium dichloroisocyanurate, chlorine dioxide and hypochlorous acid) was concentration dependent, with 1000 ppm chlorine showing reduced stability and efficacy in dirty conditions. By contrast, peracetic acid product demonstrated stability and consistently achieved efficacy in dirty conditions. CONCLUSION: These results have implications for clinical practice, as ineffective environmental decontamination may increase the risk of transmission of pathogens that can cause healthcare-associated infections.

Use of a peracetic acid (PAA) disinfectant to reduce total viable bacteria count in hospital wastewater drains.

The periphery of the hospital water system interfaces at multiple points with patients and staff in clinical areas. This comprises mostly sinks and showers and presents a significant infection control risk. Wastewater drains in particular act as a reservoir of pathogens that can be transmitted to patients. Numerous strategies have been investigated as potential methods to reduce biofilm and bacterial load including regular application of biocidal chemicals. Traditional methods of assessing the efficacy of such products relies on culture-based microbiological techniques, usually targeting a limited range of key pathogens. We assessed the efficacy of a peracetic acid containing drain disinfectant product on seven clinical handwash basin drains, taking daily samples over six weeks (before, during and after use of the drain disinfectant product). We used a rapid, culture-independent estimation of total bacterial viable count (TVC) to assess efficacy. We applied long-read metagenomic sequencing to study the entire drain microbiome, which allowed taxonomic changes to be documented following use of the drain disinfectant product. All samples were found to be heavily contaminated, however the drain disinfectant product reduced the TVC from an estimated mean of 4228 cfu/mL to 2874 cfu/mL. This reduction was sustained in the two weeks following cessation of the product. Long-read metagenomic sequencing showed a microbiome dominated with Gram-negative organisms, with some taxonomic shifts in samples before and after application of the drain disinfectant. The impact on hospital-acquired infections from reducing bioburden in hospital drains by approximately a third, along with any associated changes in bacterial composition, needs evaluation in future studies.

Image-based digital post-discharge surveillance in England: measuring patient enrolment, engagement, clinician response times, surgical site infection, and carbon footprint.

BACKGROUND: Surgical site infections (SSIs) can have a significant impact on patients, their families and healthcare providers. With shortening inpatient periods, the post-discharge element of surveillance is becoming increasingly important. Proactive surveillance, including digital wound images using patient smartphones, may be an efficient alternative to traditional methods for collecting post-discharge surveillance (PDS). AIM: To determine success in patient enrolment and engagement including reasons for non-response, the time for clinicians to respond to patients, SSI rates, and carbon emissions when conducting PDS using patient smartphones. METHODS: An evaluation was undertaken for a one-month period (June 2022) in two adult cardiac surgery services which routinely used patient smartphones for PDS, using the secure Islacare (Isla) system. FINDINGS: The initial patient response rate for Isla was 87.3%, and the majority of patients (73%) remained engaged throughout the 30-day period. There was no significant difference in age, gender, operation type or distance to hospital between Isla responders or non-responders, or if the hospital provided a photo at discharge or not. Patients using Isla had a shorter post-discharge stay (P = 0.03), although this was not attributed to the platform. Patients not owning a smartphone and a technical issue were the main barriers to participation. Overall, nine SSIs were recorded, eight through the Isla surveillance and one through a hospital transfer readmission. The carbon emission associated with the SSI ranged from 5 to 2615 kg CO2e. CONCLUSION: In a real-world setting, using patient smartphones is an effective method to collect PDS, including wound images.

SARS-CoV-2 surface and air contamination in an acute healthcare setting during the first and second pandemic waves.

BACKGROUND: Surfaces and air in healthcare facilities can be contaminated with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Previously, the authors identified SARS-CoV-2 RNA on surfaces and air in their hospital during the first wave of the coronavirus disease 2019 pandemic (April 2020). AIM: To explore whether the profile of SARS-CoV-2 surface and air contamination had changed between April 2020 and January 2021. METHODS: This was a prospective, cross-sectional, observational study in a multi-site London hospital. In January 2021, surface and air samples were collected from comparable areas to those sampled in April 2020, comprising six clinical areas and a public area. SARS-CoV-2 was detected using reverse transcription polymerase chain reaction and viral culture. Sampling was also undertaken in two wards with natural ventilation alone. The ability of the prevalent variants at the time of the study to survive on dry surfaces was evaluated. FINDINGS: No viable virus was recovered from surfaces or air. Five percent (N=14) of 270 surface samples and 4% (N=1) of 27 air samples were positive for SARS-CoV-2, which was significantly lower than in April 2020 [52% (N=114) of 218 surface samples and 48% (N=13) of 27 air samples (P<0.001, Fisher's exact test)]. There was no clear difference in the proportion of surface and air samples positive for SARS-CoV-2 RNA based on the type of ventilation in the ward. All variants tested survived on dry surfaces for >72 h, with a <3-log10 reduction in viable count. CONCLUSION: This study suggests that enhanced infection prevention measures have reduced the burden of SARS-CoV-2 RNA on surfaces and air in healthcare facilities.

Release of Ammunition-Related Compounds from a Dutch Marine Dump Site.

After World War II, large amounts of ammunition were dumped in surface waters worldwide, potentially releasing harmful and toxic compounds to the environment. To study their degradation, ammunition items dumped in the Eastern Scheldt in The Netherlands were surfaced. Severe damage due to corrosion and leak paths through the casings were observed, making the explosives in the ammunition accessible to sea water. Using novel techniques, the concentrations of ammunition-related compounds in the surrounding seabed and in the seawater were analyzed at 15 different locations. In the direct vicinity of ammunition, elevated concentrations of ammunition-related compounds (both metals and organic substances) were found. Concentrations of energetic compounds ranged from below the limit of detection (LoD) up to the low two-digit ng/L range in water samples, and from below the LoD up to the one-digit ng/g dry weight range in sediment samples. Concentrations of metals were found up to the low microgram/L range in water and up the low ng/g dry weight in sediment. However, even though the water and sediment samples were collected as close to the ammunition items as possible, the concentrations of these compounds were low and, as far as available, no quality standards or limits were exceeded. The presence of fouling, the low solubility of the energetic compounds, and dilution by the high local water current were concluded to be the main causes for the absence of high concentrations of ammunition-related compounds. As a conclusion, these new analytical methods should be applied to continuously monitor the Eastern Scheldt munitions dump site.

Utility of antimicrobial susceptibility-based algorithms for the presumptive identification of genotypically-defined community-associated methicillin-resistant Staphylococcus aureus at a London teaching hospital.

PURPOSE: Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains are classically characterised by susceptibility to most non-ß-lactam antimicrobial agents. We sought to determine whether antimicrobial susceptibility (AMS)-based algorithms could be used to presumptively identify CA-MRSA in a hospital MRSA collection. METHODS: Over a three-month period, all MRSA were tested for AMS, staphylococcal cassette chromosome mec (SCCmec) type, presence of the Panton-Valentine leukocidin (PVL) genes and spa type. CA-MRSA isolates were defined genotypically using a combination of spa and SCCmec type. AMS based algorithms were developed and tested for their sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). RESULTS: Ciprofloxacin susceptibility (p < 0.001) and fusidic acid resistance (p = 0.044) were independent predictors of CA-MRSA in a multivariate model. Although 98.5% of HA-MRSA were ciprofloxacin resistant, so too were 36.6% of CA-MRSA. Algorithms based on ciprofloxacin-susceptibility and fusidic acid resistance performed best, with specificity and NPV >90% and sensitivity and PPV >70%. CONCLUSIONS: Our data indicate that while ciprofloxacin-susceptible isolates are likely to be CA-MRSA, the use of ciprofloxacin-susceptibility as a marker of CA-MRSA would miss approximately one third of CA-MRSA isolates. Therefore, AMS patterns have limited utility for the identification of genetically-defined CA-MRSA in our setting.

Hydrogen peroxide vapour (HPV) inactivation of adenovirus.

AIMS: Adenovirus contamination can be problematic in various settings including life science laboratories and during pharmaceutical manufacturing processes. Stringent and effective decontamination procedures are necessary to minimize the risk of personnel exposure or product cross-contamination in these settings. Hydrogen peroxide vapour (HPV) is sporicidal, tuberculocidal and fungicidal with proven efficacy against some viruses. We investigate the efficacy of HPV for the inactivation of a recombinant adenovirus. METHODS AND RESULTS: In this study, the survival of a dried recombinant adenovirus (Ad5GFP) was tested before and after HPV exposure to determine the efficacy of HPV at inactivating adenovirus. A>8-log TCID(50) reduction resulted from 45-min exposure to HPV in a microbiological safety cabinet. CONCLUSIONS: HPV is effective for the inactivation of a recombinant adenovirus. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that HPV may be useful for adenovirus decontamination in life science laboratories or in manufacturing facilities.

The cost-effectiveness of temporary single-patient rooms to reduce risks of healthcare-associated infection.

BACKGROUND: The use of single rooms for patient isolation often forms part of a wider bundle to prevent certain healthcare-associated infections (HAIs) in hospitals. Demand for single rooms often exceeds what is available and the use of temporary isolation rooms may help resolve this. Changes to infection prevention practice should be supported by evidence showing that cost-effectiveness is plausible and likely. AIM: To perform a cost-effectiveness evaluation of adopting temporary single rooms into UK National Health Service (NHS) hospitals. METHODS: The cost-effectiveness of a decision to adopt a temporary, single-patient, isolation room to the current infection prevention efforts of an NHS hospital was modelled. Primary outcomes are the expected change to total costs and life-years from an NHS perspective. FINDINGS: The mean expected incremental cost per life-year gained (LYG) is £5,829. The probability that adoption is cost-effective against a £20,000 threshold per additional LYG is 93%, and for a £13,000 threshold the probability is 87%. The conclusions are robust to scenarios for key model parameters. If a temporary single-patient isolation room reduces risks of HAI by 16.5% then an adoption decision is more likely to be cost-effective than not. Our estimate of the effectiveness reflects guidelines and reasonable assumptions and the theoretical rationale is strong. CONCLUSION: Despite uncertainties about the effectiveness of temporary isolation rooms for reducing risks of HAI, there is some evidence that an adoption decision is likely to be cost-effective for the NHS setting. Prospective studies will be useful to reduce this source of uncertainty.

How dirty is your QWERTY? The risk of healthcare pathogen transmission from computer keyboards.

INTRODUCTION: Healthcare environmental surfaces may be contaminated with micro-organisms that cause healthcare-associated infections (HCAIs). Special attention is paid to near-patient surfaces but sites outside the patient zone receive less attention. This paper presents data on keyboard contamination and the risk of pathogen transmission from keyboards. METHODS: Keyboards from nursing stations in three hospitals and a dental practice were analysed for bacterial contamination. Surfaces were pre-treated to remove planktonic bacteria so that any remaining bacteria were presumed to be associated with biofilm. Bacterial transfer from keyboard keys was studied following wiping with sterile water or sodium hypochlorite. The presence of multi-drug-resistant organisms (MDROs) was sought using selective culture. RESULTS: Moist swabbing did not detect bacteria from any keyboard samples. Use of enrichment broth, however, demonstrated MDROs from most samples. Gram-negative bacteria were recovered from almost half (45%) of the samples, with meticillin-resistant Staphylococcus aureus, vancomycin-resistant enterococcus and MDR Acinetobacter spp. recovered from 72%, 31% and 17% of samples, respectively. Isolates were transferred from 69% of samples after wiping with sterile water, and from 54% of samples after wiping with 1000 ppm sodium hypochlorite. DISCUSSION: While moist swabbing failed to detect bacteria from keyboards, pathogens were recovered using enrichment culture. Use of water- or NaOCl-soaked wipes transferred bacteria from most samples tested. This study implies that hospital keyboards situated outside the patient zone commonly harbour dry surface biofilms (DSBs) that offer a potential reservoir for transferable pathogens. While the role of keyboards in transmission is uncertain, there is a need to pursue effective solutions for eliminating DSBs from keyboards.

Hospital-onset COVID-19 infection surveillance systems: a systematic review.

Hospital-onset COVID-19 infections (HOCIs) are associated with excess morbidity and mortality in patients and healthcare workers. The aim of this review was to explore and describe the current literature in HOCI surveillance. Medline, EMBASE, the Cochrane Database of Systematic Reviews, the Cochrane Register of Controlled Trials, and MedRxiv were searched up to 30 November 2020 using broad search criteria. Articles of HOCI surveillance systems were included. Data describing HOCI definitions, HOCI incidence, types of HOCI identification surveillance systems, and level of system implementation were extracted. A total of 292 citations were identified. Nine studies on HOCI surveillance were included. Six studies reported on the proportion of HOCI among hospitalized COVID-19 patients, which ranged from 0 to 15.2%. Six studies provided HOCI case definitions. Standardized national definitions provided by the UK and US governments were identified. Four studies included healthcare workers in the surveillance. One study articulated a multimodal strategy of infection prevention and control practices including HOCI surveillance. All identified HOCI surveillance systems were implemented at institutional level, with eight studies focusing on all hospital inpatients and one study focusing on patients in the emergency department. Multiple types of surveillance were identified. Four studies reported automated surveillance, of which one included real-time analysis, and one included genomic data. Overall, the study quality was limited by the observational nature with short follow-up periods. In conclusion, HOCI case definitions and surveillance methods were developed pragmatically. Whilst standardized case definitions and surveillance systems are ideal for integration with existing routine surveillance activities and adoption in different settings, we acknowledged the difficulties in establishing such standards in the short-term.

Evaluation of a personal protective equipment support programme for staff during the COVID-19 pandemic in London.

BACKGROUND: The coronavirus disease 2019 pandemic has presented an enormous challenge to healthcare providers worldwide. The appropriate use of personal protective equipment (PPE) has been essential to ensure staff and patient safety. The 'PPE Helper Programme' was developed at a large London hospital group to counteract suboptimal PPE practice. Based on a behaviour change model of capability, opportunity and motivation (COM-B), the programme provided PPE support, advice and education to ward staff. AIM: Evaluation of the PPE Helper Programme. METHODS: Clinical and non-clinical ward staff completed a questionnaire informed by the Theoretical Domains Framework and COM-B model. The questionnaire was available in paper and electronic versions. Quantitative responses were analysed using descriptive and non-parametric statistics, and free-text responses were analysed thematically. FINDINGS: Over a 6-week period, PPE helpers made 268 ward visits. Overall, 261 questionnaires were available for analysis. Across the Trust, 68% of respondents reported having had contact with a PPE helper. Staff who had encountered a PPE helper responded significantly more positively to a range of statements about using PPE than staff who had not encountered a PPE helper. Black and minority ethnic staff were significantly more anxious regarding the adequacy of PPE. Non-clinical and redeployed staff (e.g. domestic staff) were most positive about the impact of PPE helpers. Free-text comments showed that staff found the PPE Helper Programme supportive and would have liked it earlier in the pandemic. CONCLUSION: The PPE Helper Programme is a feasible and beneficial intervention for providing support, advice and education to ward staff during infectious disease outbreaks.

How do surgeons feel about the 'Getting it Right First Time' national audit? Results from a qualitative assessment.

The implementation of the national 'Getting It Right First Time' was assessed by interviewing six surgeons involved at various levels in surgical site infection (SSI) audit. The positive impacts were to create new professional collaboration, improve stakeholder engagement, and increase the profile of SSIs. One particular knowledge gap highlighted was that some participants had been unaware until that point of the criteria for diagnosing an SSI. The quality of data collected was felt to be poor due to methodological flaws. The audit was described as highly time-consuming and unsustainable if leaning on junior surgeons, without protected time and designated responsibility.

Comparison of community-associated methicillin-resistant Staphylococcus aureus from teaching hospitals in London and the USA, 2004-2006: where is USA300 in the UK?

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is increasingly common in the USA, but rare in the UK. We compared CA-MRSA from the UK and USA to examine differences in the molecular epidemiology. We investigated patients presenting with MRSA in the first 72 h of hospital admission or in out-patient settings in a UK and a US hospital from January 2004 to March 2006. Fluoroquinolone susceptibility was used as a screening marker to select presumptive CA-MRSA. One hundred and eighteen and 49 such strains were identified, representing a prevalence of 0.1 and 0.2 isolates per 1,000 patient days in the UK and US respectively. Panton-Valentine leukocidin (PVL)-positive ST8-IVa (USA300)-type strains predominated among 43 surviving US isolates, whereas PVL-negative ST1-IVa predominated among 71 surviving UK isolates. There are striking differences between the molecular epidemiology of CA-MRSA in UK and US hospitals, which may have implications for control.

Bacterial contamination on touch surfaces in the public transport system and in public areas of a hospital in London.

AIMS: To investigate bacterial contamination on hand-touch surfaces in the public transport system and in public areas of a hospital in central London. METHODS AND RESULTS: Dipslides were used to sample 118 hand-touch surfaces in buses, trains, stations, hotels and public areas of a hospital in central London. Total aerobic counts were determined, and Staphylococcus aureus isolates were identified and characterized. Bacteria were cultured from 112 (95%) of sites at a median concentration of 12 CFU cm(-2). Methicillin-susceptible Staph. aureus (MSSA) was cultured from nine (8%) of sites; no sites grew methicillin-resistant Staph. aureus (MRSA). CONCLUSIONS: Hand-touch sites in London are frequently contaminated with bacteria and can harbour MSSA, but none of the sites tested were contaminated with MRSA. SIGNIFICANCE AND IMPACT OF THE STUDY: Hand-touch sites can become contaminated with staphylococci and may be fomites for the transmission of bacteria between humans. Such sites could provide a reservoir for community-associated MRSA (CA-MRSA) in high prevalence areas but were not present in London, a geographical area with a low incidence of CA-MRSA.

Individual- and community-level risk factors for ESBL Enterobacteriaceae colonization identified by universal admission screening in London.

OBJECTIVES: We evaluated risk factors for gastrointestinal carriage of Enterobacteriaceae which produce extended-spectrum ß-lactamases (ESBL-E), including individual-level variables such as antibiotic use and foreign travel, and community-level variables such as housing and deprivation. METHODS: In an observational study in 2015, all patients admitted to a London hospital group were approached to be screened for ESBL-E carriage using rectal swabs for 4 months. Patients completed a risk factor questionnaire. Those with a residential postcode in the local catchment area were linked to a database containing community-level risk factor data. Risk factors for ESBL-E carriage were determined by binary logistic regression. RESULTS: Of 4006 patients, 360 (9.0%) carried ESBL-E. Escherichia coli was the most common organism (77.8%), and CTX-M-type ESBLs were the most common genes (57.9% CTX-M-15 and 20.7% CTX-M-9). In multivariable analysis, risk factors for phenotypic ESBL-E among the 1633 patients with a residential postcode within the local catchment area were: travel to Asia (OR 4.4, CI 2.5-7.6) or Africa (OR 2.4, CI 1.2-4.8) in the 12 months prior to admission, two or more courses of antibiotics in the 6 months prior to admission (OR 2.0, CI 1.3-3.0), and residence in a district with a higher-than-average prevalence of overcrowded households (OR 1.5, CI 1.05-2.2). . CONCLUSIONS: Both individual and community variables were associated with ESBL-E carriage at hospital admission. The novel observation that household overcrowding is associated with ESBL-E carriage requires confirmation, but raises the possibility that targeted interventions in the community could help prevent transmission of antibiotic-resistant Gram-negative bacteria.

Planning to halve Gram-negative bloodstream infection: getting to grips with healthcare-associated Escherichia coli bloodstream infection sources.

BACKGROUND: A thorough understanding of the local sources, risks, and antibiotic resistance for Escherichia coli bloodstream infection (BSI) is required to focus prevention initiatives and therapy. AIM: To review the sources and antibiotic resistance of healthcare-associated E. coli BSI. METHODS: Sources and antibiotic resistance profiles of all 250 healthcare-associated (post 48 h) E. coli BSIs that occurred within our secondary and tertiary care hospital group from April 2014 to March 2017 were reviewed. Epidemiological associations with urinary source, gastrointestinal source, and febrile neutropenia-related BSIs were analysed using univariable and multivariable binary logistic regression models. FINDINGS: E. coli BSIs increased 9% from 4.0 to 4.4 per 10,000 admissions comparing the 2014/15 and 2016/17 financial years. Eighty-nine cases (36%) had a urinary source; 30 (34%) of these were classified as urinary catheter-associated urinary tract infections (UTIs). Forty-five (18%) were related to febrile neutropenia, and 38 (15%) had a gastrointestinal source. Cases were rarely associated with surgical procedures (11, 4%) or indwelling vascular devices (seven, 3%). Female gender (odds ratio: 2.3; 95% confidence interval: 1.2-4.6) and older age (1.02; 1.00-1.05) were significantly associated with a urinary source. No significant associations were identified for gastrointestinal source or febrile neutropenia-related BSIs. Forty-seven percent of the isolates were resistant to ciprofloxacin, 37% to third-generation cephalosporins, and 22% to gentamicin. CONCLUSION: The gastrointestinal tract and febrile neutropenia together accounted for one-third of E. coli BSI locally but were rare associations nationally. These sources need to be targeted locally to reduce an increasing trend of E. coli BSIs.

Evaluating serial screening cultures to detect carbapenemase-producing Enterobacteriaceae following hospital admission.

BACKGROUND: Carbapenem-producing Enterobacteriaceae (CPE) are on the rise worldwide. National guidelines for the prevention and control of CPE recommend screening for the detection of asymptomatic carriers on admission. AIM: To evaluate the benefit of serial screens for detecting the carriage of CPE and other antibiotic-resistant Gram-negative bacteria following hospital admission. METHODS: All CPE screens, which were cultured on chromogenic media and the presence of a carbapenemase confirmed by polymerase chain reaction, were analysed for a six-month period. National guidelines in England recommend three serial screens for CPE separated by 48 h for admission screening for 'at-risk' patients, during which the patient is isolated. Two screening scenarios were tested. In scenario A, patients received three screens at the specified timepoints, in line with English national guidelines; in scenario B, patients received three consecutive screens, but not necessarily within the specified timepoints, during one admission. General linear models or conditional logistic regression were used to detect any significant change in the rate of carriage. FINDINGS: There was no significant increase in the detected carriage rate of CPE across any of the three timepoints in the scenarios tested. However, there was a significant increase in the detected rate of carriage of Gram-negative bacteria, Enterobacteriaceae, and resistant Enterobacteriaceae (excluding CPE) in scenario B. CONCLUSION: Three serial screens were not useful for the detection of CPE carriage on admission. The increase in the carriage rate of other Gram-negative bacteria may be explained by 'unmasking' of pre-existing carriage, or acquisition. This argues for regular screening of long-stay patients.