Impact of rapid molecular screening for meticillin-resistant Staphylococcus aureus in surgical wards

Performance of the Hologic Panther Fusion® MRSA Assay for the nasal screening of methicillin-sensitive and methicillin-resistant Staphylococcus aureus carriage

Staphylococcus aureus (SA) nasal carriage screening is usually based on either culture or molecular biology. The aim of the study was to evaluate the performance of the Panther Fusion® MRSA Assay (PF) that proposes a complete automation of the molecular screening for MSSA and MRSA carriage. Four hundred thirty-four nasal samples collected on ESwab™ were screened using PF. Results were compared with standard culture on BBL™ CHROMagar™ Staph aureus and chromID® MRSA agar. Discordant results were analyzed with additional techniques: Xpert SA Nasal Complete on GeneXpert (GX), culture on selective agar after 24 h in broth enrichment, and, if necessary, characterization of mec gene and SCCmec cassette using DNA microarray. The PF presented an overall agreement of 97.5% for SA detection and 97.9% for MRSA detection. Furthermore, 7.1% (31/434) of the samples were SA-negative in primary culture but SA-positive using PF and GX, confirming the greater sensitivity of molecular tests compared with culture. Of note, 4 out of 30 MRSA-positive samples were not detected due to an atypical SCCmec cassette, while 2 samples were falsely detected as MRSA due to co-colonization with a MSSA drop-out strain and a methicillin-resistant coagulase-negative staphylococcal strain. Considering all results, the PF instrument appears as a reliable and rapid (< 3 h) package for MSSA/MRSA nasal screening. This technology using random access capability and direct sampling of the primary container is innovative and corresponds therefore to a new step in complete molecular biology automation in bacteriology.

[Aortofemoral vascular graft infections and their prevention]

Vascular prosthesis infections are potentially severe adverse events following vascular reconstruction. They are often associated with a high morbidity and mortality, especially in the aortofemoral region. The present article outlines the diagnosis, prevention and treatment of vascular graft infections in a clinical setting. The clinical presentation, inflammatory markers, microbiological work-up and imaging studies can contribute to diagnosing a prosthesis infection. Regarding the bacterial spectrum involved in the etiology of prosthesis infections, single organism infections (monoinfections) have become less significant over the past years, whereas infections with multiple organisms now constitute the most abundant microbiological constellation. Also, infections with resistant bacterial strains have been increasing in number over the past years and deserve special consideration. It remains unclear whether both aspects are due to a true epidemiological change or are the result of advanced molecular microbiological diagnostic methods. While during the past decades perioperative antibiotic prophylaxis was regarded as the most important measure for preventing prosthesis infections in vascular surgery, other primary preventive hygiene strategies have been increasingly explored and grouped together in the sense of preventive bundles. In most cases of deep postoperative infections involving a prosthetic device in the aortofemoral region, explantation of the prosthesis will be required. In situ and extra-anatomical reconstructions are often performed in such cases and the decision process to develop an optimal treatment plan must consider several individual factors. In select patients, palliative preservation of the prosthesis despite surrounding infection (i.e. graft salvage) and best conservative management in combination with local surgical measures, such as incision and drainage and vacuum therapy, deserve consideration as a treatment option for patients with a high surgical risk.

The Effect of Rapid Screening for Methicillin-ResistantStaphylococcus aureus(MRSA) on the Identification and Earlier Isolation of MRSA-Positive Patients

Objectives.

(1) To determine whether rapid screening with polymerase chain reaction (PCR) assays leads to the earlier isolation of patients at risk for methicillin-resistantStaphylococcus aureus(MRSA) colonization, (2) to assess compliance with routine MRSA screening protocols, (3) to confirm the diagnostic accuracy of the Xpert MRSA real-time PCR assay (Cepheid) by comparison with culture, and (4) to compare turnaround times for PCR assay results with those for culture results.

Design.

Before-and-after study conducted in a 700-bed acute tertiary care referral hospital. Study periods were (1) a 5-week period before PCR testing began, (2) a 10-week period when the PCR assay was used, and (3) a 5-week period after PCR testing was discontinued.

Results.

Among 489 at-risk patients, MRSA was isolated from 20 (33%) of 60 patients during period 1, 77 (22%) of 349 patients during period 2, and 18 (23%) of 80 patients during period 3. Twenty-two (27%) of 82 at-risk patients were not screened during period 1, compared with 40 (10%) of 389 at-risk patients not screened during period 2 (P< .001). More MRSA-positive patients were preemptively isolated during periods 1 and 3 compared with period 2 (34 [24%] of 140 vs 28 [8%] of 389;P< .001); however, more MRSA-positive patients were isolated after notification of MRSA-positive results during period 2 (47 [13%] of 349) compared with periods 1 and 3 (2 [1%] of 140;P< .001). The sensitivity, specificity, positive predictive value, and negative predictive value of the PCR assay were 95%, 97%, 82%, and 99%, respectively. The mean turnaround time from receipt of specimens in the laboratory to PCR assay result was 2.6 hours.

Conclusions.

Rapid screening with the Xpert MRSA PCR assay facilitated compliance with screening policies and the earlier isolation of MRSA-positive Patients. Discrepant results confirm that PCR testing should be used as a screening tool rather than as a diagnostic tool.

Systematic literature analysis and review of targeted preventive measures to limit healthcare-associated infections by meticillin-resistant Staphylococcus aureus

Meticillin-resistant Staphylococcus aureus (MRSA) is a major cause of healthcare-associated infections in Europe. Many examples have demonstrated that the spread of MRSA within healthcare settings can be reduced by targeted infection control measures. The aim of this systematic literature analysis and review was to summarise the evidence for the use of bacterial cultures for active surveillance the benefit of rapid screening tests, as well as the use of decolonisation therapies and different types of isolation measures. We included 83 studies published between 2000 and 2012. Although the studies reported good evidence supporting the role of active surveillance followed by decolonisation therapy, the effectiveness of single-room isolation was mostly shown in non-controlled studies, which should inspire further research regarding this issue. Overall, this review highlighted that when planning the implementation of preventive interventions, there is a need to consider the prevalence of MRSA, the incidence of infections, the competing effect of standard control measures (e.g. hand hygiene) and the likelihood of transmission in the respective settings of implementation.

Impact of rapid molecular screening at hospital admission on nosocomial transmission of methicillin-resistant Staphylococcus aureus: cluster randomised trial

Design

Cluster randomised crossover trial with seven wards randomly allocated to intervention or control arm.

Setting

Medical and surgical wards of a university hospital with active MRSA control programme.

Participants

All patients hospitalized >48 h in study wards and screened for MRSA on admission and discharge Intervention: Rapid PCR-based screening test for MRSA compared with control screening test by enrichment culture using chromogenic agar.

Objective

We determined the benefit of PCR-detection versus culture-based detection of MRSA colonisation upon patient admission on early implementation of isolation precautions and reduction of hospital transmission of MRSA.

Main outcome

Cumulative rate of MRSA hospital acquisition of in patients screened negative on admission.

Randomization

The sequential order of inclusion of study wards in each arm was randomised by assigning a number to each ward and using a computer generated list of random numbers.

Findings

Of 3704 eligible patients, 67.8% were evaluable for the study. Compared with culture, PCR-screening reduced the median test reporting time from admission from 88 to 11 hours (p<0.001) and the median time from admission to isolation from 96 to 25 hours (p<0.001). MRSA acquisition was detected in 36 patients (3.2%) in the control arm and 34 (3.2%) in the intervention arm. The incidence density rate of hospital acquired MRSA was 2.82 and 2.57/1,000 exposed patient-days in the control and intervention arm, respectively (risk ratio 0.91 (95% confidence interval, 0.60–1.39). Poisson regression model adjusted for colonisation pressure, compliance with hand hygiene and antibiotic use indicated a RR 0.99 (95% CI, 0.69 to 1.44).

Interpretation

Universal PCR screening for MRSA on admission to medical and surgical wards in an endemic setting shortened the time to implement isolation precautions but did not reduce nosocomial acquisition of MRSA.

Trial registration

clinicaltrials.gov NCT00846105

Screening for methicillin-resistant Staphylococcus aureus: a comparative effectiveness review

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of health care-associated infections. Although the evidence in support of MRSA screening has been promising, a number of questions remain about the effectiveness of active surveillance.

METHODS

We searched the literature for studies that examined MRSA acquisition, MRSA infection, morbidity, mortality, harms of screening, and resource utilization when screening for MRSA carriage was compared with no screening or with targeted screening. Because of heterogeneity of the data and weaknesses in study design, meta-analysis was not performed. Strength of evidence (SOE) was determined using the system developed by the Grading of Recommendations Assessment, Development and Evaluation Working Group.

RESULTS

One randomized controlled trial and 47 quasi-experimental studies met our inclusion criteria. We focused on the 14 studies that addressed health care-associated outcomes and that attempted to control for confounding and/or secular trends, because those studies had the potential to support causal inferences. With universal screening for MRSA carriage compared with no screening, 2 large quasi-experimental studies found reductions in health care-associated MRSA infection. The SOE for this finding is low. For each of the other screening strategies evaluated, this review found insufficient evidence to determine the comparative effectiveness of screening.

CONCLUSIONS

Although there is low SOE that universal screening of hospital patients decreases MRSA infection, there is insufficient evidence to determine the consequences of universal screening or the effectiveness of other screening strategies.

Cost-benefit of infection control interventions targeting methicillin-resistant Staphylococcus aureus in hospitals: systematic review

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) incur significant costs. We aimed to examine the cost and cost-benefit of infection control interventions against MRSA and to examine factors affecting economic estimates. We performed a systematic review of studies assessing infection control interventions aimed at preventing spread of MRSA in hospitals and reporting intervention costs, savings, cost-benefit or cost-effectiveness. We searched PubMed and references of included studies with no language restrictions up to January 2012. We used the Quality of Health Economic Studies tool to assess study quality. We report cost and savings per month in 2011 US$. We calculated the median save/cost ratio and the save-cost difference with interquartile range (IQR) range. We examined the effects of MRSA endemicity, intervention duration and hospital size on results. Thirty-six studies published between 1987 and 2011 fulfilled inclusion criteria. Fifteen of the 18 studies reporting both costs and savings reported a save/cost ratio >1. The median save/cost ratio across all 18 studies was 7.16 (IQR 1.37-16). The median cost across all studies reporting intervention costs (n = 31) was 8648 (IQR 2025-19 170) US$ per month; median savings were 38 751 (IQR 14 206-75 842) US$ per month (23 studies). Higher save/cost ratios were observed in the intermediate to high endemicity setting compared with the low endemicity setting, in hospitals with <500-beds and with interventions of >6 months. Infection control intervention to reduce spread of MRSA in acute-care hospitals showed a favourable cost/benefit ratio. This was true also for high MRSA endemicity settings. Unresolved economic issues include rapid screening using molecular techniques and universal versus targeted screening.

Multiplex real-time PCR assay for the detection of meticillin-resistant Staphylococcus aureus and Panton-Valentine leukocidin from clinical samples

The control and prevention of meticillin-resistant Staphylococcus aureus (MRSA) is a major challenge for healthcare establishments, especially as this pathogen continues to evolve. The emergence and spread of community associated MRSA producing Panton-Valentine leukocidin (PVL) causing severe, sometimes fatal, infections in otherwise healthy people is a significant cause of concern. Patient screening to detect MRSA is now widely used as part of an effective control program to limit the spread of this pathogen. Real-time PCR targeting specific MRSA markers offers a rapid alternative to conventional methods enabling earlier intervention, such as patient isolation and decolonization treatment. Herein we describe a multiplex real-time assay that combines primers and probes to detect MRSA and the genes for PVL to provide a rapid and informative assay.

Multiplex real-time PCR assay for detection of methicillin-resistant Staphylococcus aureus (MRSA) strains suitable in regions of high MRSA endemicity

A multiplex real-time PCR assay that simultaneously detects the mecA, staphylococcal cassette chromosome (SCCmec)-open reading frame X (orfX) junction, and staphylococcal 16S rRNA genes was developed and evaluated using 444 staphylococcal strains. We demonstrated that this assay resulted in fewer false-positive results than a single-locus real-time PCR assay that amplified the SCCmec-orfX junction. This assay would be useful in a clinical laboratory in a region of high endemicity for methicillin-resistant Staphylococcus aureus (MRSA) infections.

Risk factors for previously unknown meticillin-resistant Staphylococcus aureus carriage on admission to 13 surgical wards in Europe

BACKGROUND

Early identification of meticillin-resistant Staphylococcus aureus (MRSA) carriers may be helpful for clinical and epidemiological reasons.

AIM

To identify and compare risk factors of previously unknown MRSA carriage on admission to 13 surgical wards in France, Greece, Italy, and Spain.

METHODS

The study was a prospective observational cohort study which enrolled consecutive patients screened for MRSA on admission to surgical wards. Sociodemographic data, comorbidities and possible risk factors for MRSA were recorded. A multivariate logistic regression model was used to predict probabilities of previously unknown MRSA colonization on admission based on patient characteristics. Prediction rules for MRSA carriage were developed and evaluated using the c-statistic.

FINDINGS

Of 2901 patients enrolled, admission screening identified 111 (3.8%) new MRSA carriers. Independent risk factors for MRSA carriage were urinary catheterization (odds ratio: 4.4; 95% confidence interval: 2.0-9.9), nursing home residency (3.8; 1.9-7.7), chronic skin disease (2.9; 1.5-5.8), wounds/ulcers (2.4; 1.5-4.0), recent hospitalization (2.2; 1.5-3.3), diabetes (1.6, 1.02-2.5), and age >70 years (1.5; 1.03-2.3). However, risk factors varied between centres. The c-statistic for the common prediction rule for all centres was 0.64, indicating limited predictive power.

CONCLUSIONS

Risk profiles for MRSA carriers vary between surgical wards in European countries. Identifying local risk factors is important, as a common European prediction rule was found to be of limited clinical value.

Screening, isolation, and decolonisation strategies in the control of meticillin resistant Staphylococcus aureus in intensive care units: cost effectiveness evaluation

OBJECTIVE

To assess the cost effectiveness of screening, isolation, and decolonisation strategies in the control of meticillin resistant Staphylococcus aureus (MRSA) in intensive care units.

DESIGN

Economic evaluation based on a dynamic transmission model.

SETTING

England and Wales. Population Theoretical population of patients on an intensive care unit.

MAIN OUTCOME MEASURES

Infections, deaths, costs, quality adjusted life years (QALYs), incremental cost effectiveness ratios for alternative strategies, and net monetary benefits.

RESULTS

All decolonisation strategies improved health outcomes and reduced costs. Although universal decolonisation (regardless of MRSA status) was the most cost effective in the short term, strategies using screening to target MRSA carriers may be preferred owing to the reduced risk of selecting for resistance. Among such targeted strategies, universal admission and weekly screening with polymerase chain reaction coupled with decolonisation using nasal mupirocin was the most cost effective. This finding was robust to the size of intensive care units, prevalence of MRSA on admission, proportion of patients classified as high risk, and precise value of willingness to pay for health benefits. All strategies using isolation but not decolonisation improved health outcomes but costs were increased. When the prevalence of MRSA on admission to the intensive care unit was 5% and the willingness to pay per QALY gained was between £20,000 (€23,000; $32,000) and £30,000, the best such strategy was to isolate only those patients at high risk of carrying MRSA (either pre-emptively or after identification by admission and weekly screening for MRSA using chromogenic agar). Universal admission and weekly screening using polymerase chain reaction based detection of MRSA coupled with isolation was unlikely to be cost effective unless prevalence was high (10% of patients colonised with MRSA on admission).

CONCLUSIONS

MRSA control strategies that use decolonisation are likely to be cost saving in an intensive care unit setting provided resistance is lacking, and combining universal screening using polymerase chain reaction with decolonisation is likely to represent good value for money if untargeted decolonisation is considered unacceptable. In intensive care units where decolonisation is not implemented, evidence is insufficient to support universal screening for MRSA outside high prevalence settings.

The impact of enhanced cleaning within the intensive care unit on contamination of the near-patient environment with hospital pathogens: a randomized crossover study in critical care units in two hospitals

OBJECTIVES

To determine the effect of enhanced cleaning of the near-patient environment on the isolation of hospital pathogens from the bed area and staff hands.

DESIGN

Prospective randomized crossover study over the course of 1 yr.

SETTING

Intensive care units at two teaching hospitals.

PATIENTS

There were 1252 patients staying during enhanced cleaning and 1331 staying during standard cleaning.

INTERVENTIONS

In each of six 2-month periods, one unit was randomly selected for additional twice-daily enhanced cleaning of hand contact surfaces.

MEASUREMENTS AND MAIN RESULTS

Agar contact samples were taken at five sites around randomly selected bed areas, from staff hands, and from communal sites three times daily for 12 bed days per week. Patients admitted in the year commencing April 2007 were analyzed for hospital-acquired colonization and infection. Over the course of 1152 bed days, 20,736 samples were collected. Detection of environmental methicillin-resistant Staphylococcus aureus per bed-area day was reduced during enhanced cleaning phases from 82 of 561 (14.6%) to 51 of 559 (9.1%) (adjusted odds ratio, 0.59; 95% confidence interval, 0.40-0.86; p = .006). Other targeted pathogens (Acinetobacter baumannii, extended-spectrum β-lactamase-producing Gram-negative bacteria, vancomycin-resistant enterococci, and Clostridium difficile) were rarely detected. Subgroup analyses showed reduced methicillin-resistant Staphylococcus aureus contamination on doctors' hands during enhanced cleaning (3 of 425; 0.7% vs. 11 of 423; 2.6%; adjusted odds ratio, 0.26; 95% confidence interval, 0.07-0.95; p = .025) and a trend to reduction on nurses' hands (16 of 1647; 1.0% vs. 28 of 1694; 1.7%; adjusted odds ratio 0.56; 95% confidence interval, 0.29-1.08; p = .077). All 1252 critical care patients staying during enhanced and 1,331 during standard cleaning were included, but no significant effect on patient methicillin-resistant Staphylococcus aureus acquisition was observed (adjusted odds ratio, 0.98; 95% confidence interval, 0.58-1.65; p = .93).

CONCLUSIONS

Enhanced cleaning reduced environmental contamination and hand carriage, but no significant effect was observed on patient acquisition of methicillin-resistant Staphylococcus aureus.

TRIAL REGISTRY

ISRCTN. Identifier: 06298448. http://www.controlled-trials.com/isrctn/.

Performance of the BD GeneOhm methicillin-resistant Staphylococcus aureus (MRSA) PCR assay for detecting MRSA nasal colonization in Taiwanese adults

BACKGROUND/PURPOSE

A rapid diagnostic method for methicillin-resistant Staphylococcus aureus (MRSA) has been implemented for surveillance of the at-risk population, but its performance in those without traditional risk factors is not clear. The objective of this study was to evaluate MRSA colonization status by comparing the performance of the BD GeneOhm MRSA polymerase chain reaction (PCR) assay with that of conventional culture during a 3-month active surveillance of Taiwanese adults in the community.

METHODS

From 1 October 2007 to 28 December 2007, adults (≥ 18 years old) attending a mandatory health examination arranged by their employers as a part of the workplace health promotion program at three medical centers in northern Taiwan were enrolled in the study. No healthcare workers were included. A total of 498 paired nasal swabs were prospectively obtained and used for both the BD GeneOhm MRSA PCR assay and conventional culture.

RESULTS

Of the 498 paired nasal swabs, 14 (2.8%) were positive for MRSA by conventional culture and 34 (6.8%) were positive by the BD GeneOhm MRSA PCR assay (p < 0.005). Thirteen specimens were both culture- and PCR-positive, and 463 samples were both culture- and PCR-negative. There were two discordant results: 21 specimens were culture-negative/PCR-positive, and one was culture-positive/PCR-negative. The simple kappa coefficient for measuring the agreement between conventional culture and the MRSA PCR assay was 0.52.

CONCLUSION

This study demonstrates the feasibility of using both the MRSA PCR assay and conventional culture as surveillance tools. Also, the MRSA-positive rate detected by MRSA PCR assay was significantly higher than that of conventional culture.

Modelling the costs and effects of selective and universal hospital admission screening for methicillin-resistant Staphylococcus aureus

Background

Screening at hospital admission for carriage of methicillin-resistant Staphylococcus aureus (MRSA) has been proposed as a strategy to reduce nosocomial infections. The objective of this study was to determine the long-term costs and health benefits of selective and universal screening for MRSA at hospital admission, using both PCR-based and chromogenic media-based tests in various settings.

Methodology/Principal Findings

A simulation model of MRSA transmission was used to determine costs and effects over 15 years from a US healthcare perspective. We compared admission screening together with isolation of identified carriers against a baseline policy without screening or isolation. Strategies included selective screening of high risk patients or universal admission screening, with PCR-based or chromogenic media-based tests, in medium (5%) or high nosocomial prevalence (15%) settings. The costs of screening and isolation per averted MRSA infection were lowest using selective chromogenic-based screening in high and medium prevalence settings, at $4,100 and $10,300, respectively. Replacing the chromogenic-based test with a PCR-based test costs $13,000 and $36,200 per additional infection averted, and subsequent extension to universal screening with PCR would cost $131,000 and $232,700 per additional infection averted, in high and medium prevalence settings respectively. Assuming $17,645 benefit per infection averted, the most cost-saving strategies in high and medium prevalence settings were selective screening with PCR and selective screening with chromogenic, respectively.

Conclusions/Significance

Admission screening costs $4,100–$21,200 per infection averted, depending on strategy and setting. Including financial benefits from averted infections, screening could well be cost saving.

Rapid molecular screening for meticillin-sensitive Staphylococcus aureus (MSSA) carriage: an economic evaluation

Aim: To establish the cost-effectiveness of screen-A ing and treating meticillin-sensitive Staphylococcus aureus (MSSA) carriers, potentially reducing both financial and clinical burdens of managing healthcare-acquired infections.

Methods: A decision health economic model analysed the impact of a ‘screen and treat’ strategy for Hospital inpatients from the perspective of the UK National Health Service.

Results: Cost savings in excess of £600k and around 840 potential infections could be avoided in a 70,000 patient cohort, at a nasal carriage prevalence of 30%. For 2000 high infection risk cardiothoracic surgery patients, cost savings could reach £8,636 per annum. The dominance of the ‘screen and treat’ strategy holds for plausible variations in the model parameter values and simple modelling of secondary transmission.

Conclusion: Adopting rapid screening and treating MSSA nasal carriers should be clinically and financially advantageous, compared to current strategies of not screening, even under conservative assumptions for costs and probabilities of managing infections.

Real-time evaluation of an optimized real-time PCR assay versus Brilliance chromogenic MRSA agar for the detection of meticillin-resistant Staphylococcus aureus from clinical specimens

A total of 1204 meticillin-resistant Staphylococcus aureus (MRSA) screens (3340 individual swabs) were tested to evaluate a staphylococcal cassette chromosome mec (SCCmec) real-time PCR. In total, 148 (12.3 %) of the screens were MRSA-positive, where 146 (12.1 %) were MRSA-positive by the SCCmec real-time PCR assay. In contrast, 128 (10.6 %) screens were MRSA-positive by culture. One hundred and twenty-six (10.5 %) of the screens were positive by both culture and PCR. Twenty of the 1204 screens (1.66 %) were negative by culture but positive by PCR; these samples were sequenced. In 14 of the cases, a homology search confirmed the sequence as SCCmec, indicating that these samples could be considered true positives. Two of the 1204 (0.2 %) screens were positive by culture and negative by PCR. The mean turnaround time (TAT) for PCR-negative swabs was 6 h 12 min and for PCR-positive swabs was 6 h 48 min. In comparison, for culture-negative swabs the mean TAT was 29 h 30 min and for culture-positive swabs was 69 h. The cost per swab for routine culture was £0.41 (€0.48) and that of the real-time PCR assay was £2.35 (€2.75). This optimized, in-house, inexpensive, real-time PCR test maintained a very high sensitivity and specificity when evaluated under real-time laboratory conditions. The TAT of this real-time PCR assay was substantially lower than that of chromogenic culture. It was also maintained throughout the entire process, which can be taken as an indirect measure of test performance. This study showed that implementation of a molecular test can be achieved with limited resources in a standard microbiology laboratory.

Preventing surgical site infections

The risk of surgical site infection (SSI) is approximately 1-3% for elective clean surgery. Apart from patient endogenous factors, the role of external risk factors in the pathogenesis of SSI is well recognized. However, among the many measures to prevent SSI, only some are based on strong evidence, for example, adequate perioperative administration of prophylactic antibiotics, and there is insufficient evidence to show whether one method is superior to any other. This highlights the need for a multimodal approach involving active post-discharge surveillance, as well as measures at every step of the care process, ranging from the operating theater to postoperative care. Multicenter or supranational intervention programs based on evidence-based guidelines, 'bundles' or safety checklists are likely to be beneficial on a global scale. Although theoretically reducible to zero, the maximal realistic extent by which SSI can be decreased remains unknown.

Evaluation of the Xpert MRSA assay for rapid detection of methicillin-resistant Staphylococcus aureus from nares swabs of geriatric hospitalized patients and failure to detect a specific SCCmec type IV variant

Rapid and reliable detection of methicillin-resistant Staphylococcus aureus (MRSA) carriers is crucial for control of MRSA nosocomial transmission. We aimed to evaluate the performance of the GeneXpert real-time PCR system using the Xpert MRSA assay on a collection of 40 representative Belgian MRSA strains and for MRSA screening of geriatric inpatients. Double nasal swabs were used: the first swab for the Xpert MRSA assay and the second for culture onto chromogenic selective medium and enrichment broth. All but 1 of the 40 collection strains were recognized as MRSA by the Xpert MRSA assay. Nares swabs were prospectively collected from 246 inpatients including 25 nasal MRSA carriers. Compared with enriched cultures, the sensitivity, the specificity, and the positive and negative predictive values of the Xpert MRSA assay were 69.2%, 97.7%, 78.3%, and 96.3% respectively. The 7 evaluable false-negative results according to the assay were due to its possible lack of sensitivity (n = 3) and to the occurrence of a Belgian MRSA clone carrying a particular staphylococcal chromosomal cassette mec (SCCmec) type IV variant (n = 4) not targeted by the current Xpert MRSA assay. Because of the evolution of SCCmec in MRSA, new primers should be designed and further studies are warranted to ensure continuous monitoring of this assay.

Can 'search and destroy' reduce nosocomial methicillin-resistant Staphylococcus aureus in an Irish hospital?

In Ireland, the Department of Health and Children recommends admission screening of patients at increased risk of methicillin-resistant Staphylococcus aureus (MRSA), isolation of these patients until proven negative, and eradication of any MRSA identified. These actions form the basis of a programme called 'search and destroy' that has successfully reduced MRSA in Scandinavia. There is, however, very little information published on the use of search and destroy in Ireland. This study was carried out using a quantitative, quasi-experimental design in the form of an interventional cohort study. The effect of reducing the turnaround time for MRSA results (2007) and the introduction of pre-emptive isolation (2008) was examined in a hospital with an established admission screening programme for MRSA. Rates of MRSA infection and colonisation were monitored post-intervention and compared to baseline rates prior to the intervention (2005-2006). Rates of hospital-acquired (nosocomial) MRSA infections and colonisation fell in both 2007 and 2008. However, due to the quasi-experimental design of the study and the low endemic level of MRSA in the hospital, a causal link could not be established.

Feasibility study of a real-time PCR test for meticillin-resistant Staphylococcus aureus in a point of care setting

We investigated whether a commercial real-time polymerase chain reaction test for meticillin-resistant Staphylococcus aureus (MRSA) could be used as a point of care test. GeneXpert systems, on which the Xpert MRSA test is run, were installed on four wards within the Sandwell and West Birmingham Hospitals NHS Trust and in the main microbiology laboratory. Nasal samples were collected using double-headed swabs from newly admitted patients onto the four study wards. One swab was tested using the Xpert MRSA test on the ward by non-laboratory staff, the other was tested by the microbiology laboratory. In total, 988 nasal swabs were collected from 930 patients (March 2008 to June 2008). Of these, 947 processed swabs gave a valid result (MRSA positive or negative) both in the laboratory and respective ward, and there was 97.5% agreement between results obtained from the ward and from the laboratory (850 MRSA negative; 73 MRSA positive). Results for 24 swabs showed a discrepancy between the results from the ward and laboratory. MRSA testing carried out on the wards showed a sensitivity, specificity, positive predictive value and negative predictive value of 83.9, 98.8, 88.0 and 98.4, respectively, compared with the laboratory. On average the time to result for the wards was >10h quicker than the laboratory. The Xpert MRSA test performed equally well, whether carried out on the wards or by the laboratory. The major benefit of MRSA point of care testing was the large reduction in the time to obtain a result compared with the laboratory.

Screening and isolation for infection control

Control measures aimed to reduce the prevalence of healthcare-associated infections include active surveillance cultures (ASCs), contact isolation of patients colonised with epidemiologically significant pathogens, and pre-emptive isolation of high risk patients. However, the benefits of these measures are questionable. A systematic review of isolation policies demonstrated that intensive concerted interventions including isolation can substantially reduce nosocomial meticillin-resistant Staphylococcus aureus (MRSA) infection. Monitoring of interventions is fundamental. Surveillance data should be presented and fed back appropriately. International guidelines suggest that only intensive care units should apply extensive ASCs. However, legislation for mandatory screening at hospital admission has been advocated in many countries. Targeted screening could be used to limit the potential for dissemination of antibiotic-resistant pathogens from otherwise unsuspected carriers from the start of patients' hospitalisation, as opposed to other strategies, in which screening programmes target patients already hospitalised. Although the influx of antibiotic-resistant pathogens into the hospital would not change, early detection would reduce the time colonised patients might have to disseminate pathogens. Recently, rapid methods for molecular detection of MRSA have been developed. Data on the impact of these tests on the MRSA acquisition rate are extremely heterogeneous. Published studies differ according to the settings in which they have been evaluated, the choice of patient population to be screened, other infection control measures employed and, most importantly, study design and baseline prevalence of MRSA. Based on these studies, definitive recommendations cannot be made.

Comparative evaluation of a rapid MRSA detection assay based on multiplex real-time PCR versus MRSA screening cultures containing egg yolk

Although the Centers for Disease Control and Prevention (CDC) has been recommending the performance of active surveillance culture (ASC) for the prevention of methicillin-resistant Staphylococcus aureus (MRSA) infections and their control since the guideline was issued in 2006, many variant types of MRSA with various characteristics have been found recently. As this change in MRSA characteristics makes it harder to screen MRSA only by cultures, it is expected that ASC will not be sufficient for the prevention of MRSA infections or MRSA infection control. We evaluated the comparative utility of the BD GeneOhm MRSA assay (a rapid MRSA detection test based on a multiplex real-time polymerase chain reaction [PCR] assay; Becton Dickinson, Fukushima, Japan) and MRSA screening cultures containing egg yolk. The results of the BD GeneOhm MRSA assay were as follows: all MRSA strains were positive, including one strain which became positive by retest; all methicillin-resistant S. epidermidis (MRSE) strains and methicillin-sensitive S. epidermidis (MSSE) strains were negative; 11 of 12 methicillin-sensitive S. aureus (MSSA) strains were negative, while 1 strain was positive; ATCC 33591 was positive, and ATCC 29213 was negative. The sensitivity and specificity of the BD GeneOhm MRSA assay were 100% and 97.4%, respectively. Nine egg yolk reaction-negative MRSA strains were found in 50 MRSA strains, and all MRSE, MSSA, and MSSE strains were denied as MRSA on Pourmedia MRSA II (Eiken Chemical, Tokyo, Japan) after 24-h or 48-h incubation at 35 degrees C. The sensitivity and specificity of Pourmedia MRSA II were 82% and 100%, respectively. Similar results were obtained with some other cultures containing egg yolk.

Cost-effectiveness of rapid MRSA screening in surgical patients

This study investigates the effectiveness of a same-day polymerase chain reaction (PCR) test for the rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) in a general screening of patients admitted to the trauma surgery and heart surgery department in a German university hospital. A total of 442 patients were screened over a 4-month period by using a PCR assay, compared to culture methods, for specimens from the nose and throat. The MRSA carriage rate on admission was 3.85% during the study period. The PCR results of 1,680 swabs showed a sensitivity of 85% and a specificity of 99.39% for swabs from the nares and for the throat 42.11% and 98.78%, respectively. A combination of specimens from the nose and throat from the same patient led to a sensitivity of 100% with a specificity of 98.29%. Cost calculation under the circumstances of a diagnosis-related groups (DRG) payment system found that the eight MRSA-positive patients created costs of 38,472 euros, i.e. 4,809 euros per patient, facing screening costs of 36.62 euros per sample. Screening patients by using the rapid PCR assay for a combination of specimens from the nose and throat would offer a safe and cost-effective way of MRSA screening on admission.

Health Care-Associated Infection Prevention and Control: Pharmacists' Role in Meeting National Patient Safety Goal 7

Health care-associated infections and antimicrobial resistance are continually increasing, with fewer drugs available for effective treatment. Potential benefits of infection control and antimicrobial stewardship programs include improvements in antibiotic use and conversion from intravenous (IV) to oral antibiotics and reductions in resistance and infection rates and length of hospital stay. NorthShore University HealthSystem in Evanston, Illinois, was the first large hospital system in North America that adopted universal inpatient surveillance for methicillin-resistant Staphylococcus aureus (MRSA). Results showed that nasal MRSA was a powerful predictor of MRSA disease and antibiotic resistance in other organisms. MRSA infections occurring up to 30 days posthospitalization decreased by approximately 70%. At the Hospital of Saint Raphael, a community teaching hospital in New Haven, Connecticut, an antimicrobial stewardship pilot program focused on automatic conversation from IV to oral antimicrobials and appropriate antimicrobial use. The percentage of patients receiving oral fluconazole increased from 63% to 77%; the percentage of those receiving oral linezolid increased from 54% to 71%. Total antibiotic use decreased by 6%. Based on the 60-day trial, potential cost savings were estimated as $874,000 annually, less the cost of a pharmacist's salary and benefits. Infection control and antimicrobial stewardship programs offer pharmacists new opportunities for helping improve patient safety and quality of care. Pharmacy-medical staff partnership, combined with support from microbiology, infection control, information technology, and hospital administration, is key to a successful program.

Screening for MRSA

Rapid screening is no more effective at reducing acquisition than conventional screening

Impact of rapid screening tests on acquisition of meticillin resistant Staphylococcus aureus: cluster randomised crossover trial

OBJECTIVE

To determine whether introducing a rapid test for meticillin resistant Staphylococcus aureus (MRSA) screening leads to a reduction in MRSA acquisition on hospital general wards.

DESIGN

Cluster randomised crossover trial.

SETTING

Medical, surgical, elderly care, and oncology wards of a London teaching hospital on two sites.

MAIN OUTCOME MEASURE

MRSA acquisition rate (proportion of patients negative for MRSA who became MRSA positive).

PARTICIPANTS

All patients admitted to the study wards who were MRSA negative on admission and screened for MRSA on discharge.

INTERVENTION

Rapid polymerase chain reaction based screening test for MRSA compared with conventional culture.

RESULTS

Of 9608 patients admitted to study wards, 8374 met entry criteria and 6888 had full data (82.3%); 3335 in the control arm and 3553 in the rapid test arm. The overall MRSA carriage rate on admission was 6.7%. Rapid tests led to a reduction in median reporting time from admission, from 46 to 22 hours (P<0.001). Rapid testing also reduced the number of inappropriate pre-emptive isolation days between the control and intervention arms (399 v 277, P<0.001). This was not seen in other measurements of resource use. MRSA was acquired by 108 (3.2%) patients in the control arm and 99 (2.8%) in the intervention arm. When predefined confounding factors were taken into account the adjusted odds ratio was 0.91 (95% confidence interval 0.61 to 1.234). Rates of MRSA transmission, wound infection, and bacteraemia were not statistically different between the two arms.

CONCLUSION

A rapid test for MRSA led to the quick receipt of results and had an impact on bed usage. No evidence was found of a significant reduction in MRSA acquisition and on these data it is unlikely that the increased costs of rapid tests can be justified compared with alternative control measures against MRSA.

TRIAL REGISTRATION

Clinical controlled trials ISRCTN75590122 [controlled-trials.com].