Prospective study of infection, colonization and carriage of methicillin-resistant Staphylococcus aureus in an outbreak affecting 990 patients

Characterization of the best anatomical sites in screening for methicillin-resistant Staphylococcus aureus colonization

The purpose of this study was to identify differences in the sensitivity of anatomical sites sampling for methicillin-resistant Staphylococcus aureus (MRSA) colonization related to age, gender, clinical situation, and acquisition source as a base for screening protocols. We used a database that included all MRSA-positive cultures (Carmel Medical Center, 2003-2006) taken from nares, throat, perineum, and infection sites. The study population of 597 patients was divided into: "screening sample" (SS), which were cases of routine screening, and "clinical diagnostic sample" (CDS), which were patients with concurrent MRSA infection. MRSA acquisition sources were classified as internal medicine, surgical, referral patients, or intensive care unit (ICU). CDS patients were older than SS patients (median age 78 vs. 74 years, p = 0.0002), more commonly throat colonized (47.5% vs. 31.8%, p = 0.0001), and colonized in more multiple sites (65.7% vs. 43.3% were colonized in three sites in the CDS and SS groups, respectively, p < 0.001) than SS patients. In the SS, group throat colonization was higher in internal medicine wards than in the ICU (odds ratio [OR] = 3.98, p < 0.0001). In the CDS group, perineal colonization was more common in referral patients than in the ICU (OR = 4.52, p < 0.05). Patient age was the most influential factor on nares and multiple sites colonization in the SS and CDS groups, respectively. Our data support multiple sites sampling. Throat cultures are crucial in MRSA-infected patients and internal medicine ward patients. Multiple body sites colonization is more likely in older or MRSA-infected patients, affecting decisions regarding eradication using topical antibiotics.

Effectiveness of universal screening for vancomycin-resistant enterococcus and methicillin-resistant Staphylococcus aureus on admission to a burn-trauma step-down unit

Vancomycin-resistant enterococcus (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) are significant healthcare-associated pathogens. We sought to identify factors that could be used to predict which patients carry or are infected with VRE or MRSA on admission so that we could obtain cultures selectively from high-risk patients on our burn-trauma unit. We conducted a case-control study of patients admitted to our burn-trauma unit from September 2000 to March 2005 who were colonized or infected with either VRE or MRSA (cases) and patients who were not colonized or infected with one of these organisms (controls). We used logistic regression to construct a model that we subsequently validated based on data collected prospectively from patients admitted from September 2006 to August 2007. In the case-control study, colonization or infection with MRSA or VRE on admission were independently associated with the total days of antimicrobial treatment, age, prior hospitalization, prior operations, and admitting diagnosis (admission for a burn injury was protective). In the cohort study, a prior hospitalization with a length of stay>or=7 days and operations within the past 6 months were significantly associated with colonization or infection on admission. The latter model was 59.3% sensitive. If, we used this model to identify which patients should be cultured on admission, we would have missed 24 (39.3%) of the colonized or infected patients. These patients would not have been placed in isolation (434 missed isolation days, 71.0%) and may have been the source of transmission to other patients. Our model lacked the sensitivity to identify patients colonized or infected with VRE or MRSA. We recommend that units, which care for patients who are at high risk of hospital-acquired infection and having prevalence and transmission rates of VRE or MRSA similar to those in our study, screen all patients for these organisms on admission to the unit.

Surveillance cultures for detection of methicillin-resistant Staphylococcus aureus: diagnostic yield of anatomic sites and comparison of provider- and patient-collected samples

We studied provider- and patient-collected samples from multiple anatomic sites to determine the yield for detection of methicillin-resistant Staphylococcus aureus (MRSA). Sampling of multiple sites was required to achieve a sensitivity of more than 90% for MRSA colonization. Groin and perineum samples yielded positive results significantly more often for community-onset MRSA than for hospital-onset MRSA. Agreement rates between provider- and patient-collected swab specimens were excellent.

Acquisition and cross-transmission of Staphylococcus aureus in European intensive care units

OBJECTIVE

To study the acquisition and cross-transmission of Staphylococcus aureus in different intensive care units (ICUs).

METHODS

We performed a multicenter cohort study. Six ICUs in 6 countries participated. During a 3-month period at each ICU, all patients had nasal and perineal swab specimens obtained at ICU admission and during their stay. All S. aureus isolates that were collected were genotyped by spa typing and multilocus variable-number tandem-repeat analysis typing for cross-transmission analysis. A total of 629 patients were admitted to ICUs, and 224 of these patients were found to be colonized with S. aureus at least once during ICU stay (22% were found to be colonized with methicillin-resistant S. aureus [MRSA]). A total of 316 patients who had test results negative for S. aureus at ICU admission and had at least 1 follow-up swab sample obtained for culture were eligible for acquisition analysis.

RESULTS

A total of 45 patients acquired S. aureus during ICU stay (31 acquired methicillin-susceptible S. aureus [MSSA], and 14 acquired MRSA). Several factors that were believed to affect the rate of acquisition of S. aureus were analyzed in univariate and multivariate analyses, including the amount of hand disinfectant used, colonization pressure, number of beds per nurse, antibiotic use, length of stay, and ICU setting (private room versus open ICU treatment). Greater colonization pressure and a greater number of beds per nurse correlated with a higher rate of acquisition for both MSSA and MRSA. The type of ICU setting was related to MRSA acquisition only, and the amount of hand disinfectant used was related to MSSA acquisition only. In 18 (40%) of the cases of S. aureus acquisition, cross-transmission from another patient was possible.

CONCLUSIONS

Colonization pressure, the number of beds per nurse, and the treatment of all patients in private rooms correlated with the number of S. aureus acquisitions on an ICU. The amount of hand disinfectant used was correlated with the number of cases of MSSA acquisition but not with the number of cases of MRSA acquisition. The number of cases of patient-to-patient cross-transmission was comparable for MSSA and MRSA.

Methicillin-resistant Staphylococcus aureus in orthopaedic surgery

Methicillin-resistant Staphylococcus aureus (MRSA) has become a ubiquitous bacterium in both the hospital and community setting. There are two major subclassifications of MRSA, community-acquired and healthcare-acquired, each with differing pathogenicity and management. MRSA is increasingly responsible for infections in otherwise healthy, active adults. Local outbreaks affect both professional and amateur athletes and there is increasing public awareness of the issue. Health-acquired MRSA has major cost and outcome implications for patients and hospitals. The increasing prevalence and severity of MRSA means that the orthopaedic community should have a basic knowledge of the bacterium, its presentation and options for treatment. This paper examines the evolution of MRSA, analyses the spectrum of diseases produced by this bacterium and presents current prevention and treatment strategies for orthopaedic infections from MRSA.

A randomized controlled trial of tea tree oil (5%) body wash versus standard body wash to prevent colonization with methicillin-resistant Staphylococcus aureus (MRSA) in critically ill adults: research protocol

Background

Over the past ten years MRSA has become endemic in hospitals and is associated with increased healthcare costs. Critically ill patients are most at risk, in part because of the number of invasive therapies that they require in the intensive care unit (ICU). Washing with 5% tea tree oil (TTO) has been shown to be effective in removing MRSA on the skin. However, to date, no trials have evaluated the potential of TTO body wash to prevent MRSA colonization or infection. In addition, detecting MRSA by usual culture methods is slow. A faster method using a PCR assay has been developed in the laboratory, but requires evaluation in a large number of patients.

Methods/Design

This study protocol describes the design of a multicentre, phase II/III prospective open-label randomized controlled clinical trial to evaluate whether a concentration of 5% TTO is effective in preventing MRSA colonization in comparison with a standard body wash (Johnsons Baby Softwash) in the ICU. In addition we will evaluate the cost-effectiveness of TTO body wash and assess the effectiveness of the PCR assay in detecting MRSA in critically ill patients. On admission to intensive care, swabs from the nose and groin will be taken to screen for MRSA as per current practice. Patients will be randomly assigned to be washed with the standard body wash or TTO body wash. On discharge from the unit, swabs will be taken again to identify whether there is a difference in MRSA colonization between the two groups.

Discussion

If TTO body wash is found to be effective, widespread implementation of such a simple colonization prevention tool has the potential to impact on patient outcomes, healthcare resource use and patient confidence both nationally and internationally.

Trial Registration

[ISRCTN65190967]

The role of healthcare personnel in the maintenance and spread of methicillin-resistant Staphylococcus aureus

Healthcare workers may acquire methicillin-resistant Staphylococcus aureus (MRSA) from patients, both hospital and home environments, other healthcare workers, family and public acquaintances, and pets. There is a consensus of case reports and series which now strongly support the role for MRSA-carrying healthcare personnel to serve as a reservoir and as a vehicle of spread within healthcare settings. Carriage may occur at a number of body sites and for short, intermediate, and long terms. A number of approaches have been taken to interrupt the linkage of staff-patient spread, but most emphasis has been placed on handwashing and the treatment of staff MRSA carriers. The importance of healthcare workers in transmission has been viewed with varying degrees of interest, and several logistical problems have arisen when healthcare worker screening is brought to the forefront. There is now considerable support for the screening and treatment of healthcare workers, but it is suggested that the intensity of any such approach must consider available resources, the nature of the outbreak, and the strength of epidemiological associations. The task of assessing healthcare personnel carriage in any context should be shaped with due regard to national and international guidelines, should be honed and practiced according to local needs and experience, and must be patient-oriented.

Epidemiologic genotyping of methicillin-resistant Staphylococcus aureus (MRSA) by pulsed-field gel electrophoresis (PFGE)

Staphylococcus aureus has long been recognized as one of the leading cause of hospital infections all over the world. Increased frequency of methicillin-resistant Staphylococcus aureus (MRSA) in hospitalized patients and possibility of vancomycin resistance requires rapid and reliable characterization of isolates and control of MRSA spread in hospitals. Typing of isolates helps to understand pathogenesis and route of the hospital pathogen spread. In this study, in the analysis of an outbreak of MRSA infections in one surgical ward, we used pulsed-field gel electrophoresis (PFGE) as a method of typing. PFGE revealed one epidemic strain type A in 13 out of 16 patients, and another two types (type B in two patients and type C in one patient). Discussing the typing results in the ward has changed the admission policy of patients with infected vascular ulcers who were then cured as outpatients, and admitted for surgery after that. This policy resulted with the stopping of the outbreak; during next 2.5 year there was no further MRSA outbreak in the ward. PFGE also showed subtypes which enabled the insight into dynamics of MRSA strain changes during the outbreak. PFGE could be recommended as a screening method in the MRSA outbreak analysis. Because of it's high discriminatory power still remains the gold standard for MRSA typing.

Bacteriophage lysins as effective antibacterials

Lysins are highly evolved enzymes produced by bacteriophage (phage for short) to digest the bacterial cell wall for phage progeny release. In Gram-positive bacteria, small quantities of purified recombinant lysin added externally results in immediate lysis causing log-fold death of the target bacterium. Lysins have been used successfully in a variety of animal models to control pathogenic antibiotic resistant bacteria found on mucosal surfaces and infected tissues. The advantages over antibiotics are their specificity for the pathogen without disturbing the normal flora, the low chance of bacterial resistance to lysins, and their ability to kill colonizing pathogens on mucosal surfaces, a capacity previously unavailable. Thus, lysins may be a much needed anti-infective in an age of mounting antibiotic resistance.

Intestinal carriage of Staphylococcus aureus: how does its frequency compare with that of nasal carriage and what is its clinical impact?

The bacterial species Staphylococcus aureus, including its methicillin-resistant variant (MRSA), finds its primary ecological niche in the human nose, but is also able to colonize the intestines and the perineal region. Intestinal carriage has not been widely investigated despite its potential clinical impact. This review summarizes literature on the topic and sketches the current state of affairs from a microbiological and infectious diseases' perspective. Major findings are that the average reported detection rate of intestinal carriage in healthy individuals and patients is 20% for S. aureus and 9% for MRSA, which is approximately half of that for nasal carriage. Nasal carriage seems to predispose to intestinal carriage, but sole intestinal carriage occurs relatively frequently and is observed in 1 out of 3 intestinal carriers, which provides a rationale to include intestinal screening for surveillance or in outbreak settings. Colonization of the intestinal tract with S. aureus at a young age occurs at a high frequency and may affect the host's immune system. The frequency of intestinal carriage is generally underestimated and may significantly contribute to bacterial dissemination and subsequent risk of infections. Whether intestinal rather than nasal S. aureus carriage is a primary predictor for infections is still ill-defined.

Sensitivities of nasal and rectal swabs for detection of methicillin-resistant Staphylococcus aureus colonization in an active surveillance program

All medical and high-risk surgical patients were screened for methicillin-resistant Staphylococcus aureus colonization over 3.5 years. The sensitivities of nasal and rectal swabs were 68% and 62%, respectively. Naris and open-skin-site swabs detected 467 (74%) of 627 adult carriers identified. Rectal swabs detected an additional 160 (26%) carriers.

Health-care workers: source, vector, or victim of MRSA?

There is ongoing controversy about the role of health-care workers in transmission of meticillin-resistant Staphylococcus aureus (MRSA). We did a search of the literature from January, 1980, to March, 2006, to determine the likelihood of MRSA colonisation and infection in health-care workers and to assess their role in MRSA transmission. In 127 investigations, the average MRSA carriage rate among 33 318 screened health-care workers was 4.6%; 5.1% had clinical infections. Risk factors included chronic skin diseases, poor hygiene practices, and having worked in countries with endemic MRSA. Both transiently and persistently colonised health-care workers were responsible for several MRSA clusters. Transmission from personnel to patients was likely in 63 (93%) of 68 studies that undertook genotyping. MRSA eradication was achieved in 449 (88%) of 510 health-care workers. Subclinical infections and colonisation of extranasal sites were associated with persistent carriage. We discuss advantages and disadvantages of screening and eradication policies for MRSA control and give recommendations for the management of colonised health-care workers in different settings.

Methicillin-resistant Staphylococcus aureus carriage in a long-term care facility: hypothesis about selection and transmission

BACKGROUND

many studies have identified long-term care facilities (LTCFs) as reservoirs of patients carrying methicillin-resistant Staphylococcus aureus (MRSA). However, few data about the mechanisms of MRSA diffusion in these settings are available.

OBJECTIVES

the purpose of our study was to suggest hypothesis on the possible ways of MRSA transmission to residents in or outside a LTCF.

METHODS

data concerning patients on the day of the survey and within the preceding year were collected. Multivariate analysis was performed by logistic regression to identify characteristics associated with MRSA carriage. MRSA strains were analysed by pulsed-field gel electrophoresis (PFGE) and the relatedness between DNA patterns was studied with Gel Compar software.

RESULTS

the prevalence of MRSA carriage was 37.6%. Treatment with fluoroquinolones or third-generation cephalosporins [odds ratio (OR) = 12.07; 95% confidence interval (CI) = 5.90-24.7], treatment with other antimicrobial agents (OR = 4.40; 95% CI = 2.43-7.97), at least one medical imaging session (OR = 5.08; 95% CI = 2.66-9.69) within the 12 preceding months, and the presence of a subcutaneous catheter on the day of the survey (OR = 3.09; 95% CI = 1.87-5.10) were independently associated with MRSA carriage. Twenty-eight of the 38 strains tested were clustered in two major groups. In each of these groups, strains had at least a 90% relatedness. These strains were isolated in patients hospitalised in different areas of the LTCF.

CONCLUSION

we identified that both molecular and epidemiological arguments support the hypothesis of the possibility of MRSA cross-transmission inside the LTCF. Further studies are needed to confirm and explain the association identified between MRSA carriage and medical imaging.

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].

Is an increase of MRSA in Oslo, Norway, associated with changed infection control policy?

OBJECTIVES

The objective was to describe the prevalence of MRSA in Oslo, Norway, before and after introduction of a new National MRSA Control Guideline.

METHODS

From 1993 to 2006, we prospectively collected clinical and microbiological data on all MRSA cases in Oslo, Norway. Two MRSA guidelines; a strict Ullevål Standard MRSA Guideline and a less strict National MRSA Control Guideline were compared.

RESULTS

During 1993-2006, 358 MRSA cases were registered in Oslo; 43.9% detected in Ullevål University Hospital, 21.2% in nursing homes, and 18.7% in primary healthcare. One out of three (30.4%) were import-associated, and one out of ten (11.2%) were healthcare personnel. From 2004 on, a new National MRSA Control Guideline was introduced in primary healthcare, served by the community infection control. From 2004 on, there was a 4-6-fold increase of MRSA in primary healthcare (p = 0.038) and nursing homes (p = 0.005). Increase of MRSA cases at Ullevål (p < 0.001) was import-associated or from outbreaks in primary healthcare. There was no increase of internal spread in the hospital.

CONCLUSION

These data indicate that perhaps a less strict national MRSA infection control guideline in Norway may be associated with the 4-6-fold increase of MRSA cases in the community after 2003.

Validation of the IDI-MRSA system for use on pooled nose, axilla, and groin swabs and single swabs from other screening sites

A commercial rapid polymerase chain reaction methicillin-resistant Staphylococcus aureus (MRSA) screening method (IDI-MRSA) is validated for the use with nasal swabs transported in liquid Stuart's medium. We investigated the use of IDI-MRSA for screening for MRSA in pooled nose, axilla, and groin swabs and in single swabs from skin puncture sites, wounds, throat, rectum, and groin using swabs transported in Amies medium without charcoal. We performed the IDI-MRSA test on swabs that had been used for routine MRSA broth culture and which were selected to be about 50% MRSA positive. We compared the IDI-MRSA result with the MRSA culture result. With 201 pooled sets, the sensitivity of IDI-MRSA was 85% and the specificity 95%. With 32 single screening swabs, sensitivity was 94% and specificity 80%. The method is not compromised by swab transport in Amies medium if an additional heating step is used. We had a low rate of initial inhibition (1.3%), which may have been due to the extra heating step used to liquefy gel from the Amies medium. Thus, in this study IDI-MRSA gives similar results to culture with pooled or single swabs from multiple screening sites.

Financial implications of plans to combat methicillin-resistant Staphylococcus aureus (MRSA) in an orthopaedic department

INTRODUCTION

The aim of this study was to calculate retrospectively the cost of MRSA infections in the elective and trauma orthopaedic population in Rotherham District General Hospital in a 3-month period during 2005.

PATIENTS AND METHODS

A total of 686 patients were admitted to the orthopaedic wards and the surgical wounds 10 patients became infected with MRSA.

RESULTS

The cost of these infections when extrapolated over 12 months was pound384,000 excluding staff costs.

CONCLUSIONS

The key in the fight against MRSA in the hospital setting is multifactorial and requires a combination of measures. Our solution is: cohort nursing; non-selective screening of all admissions to the orthopaedic wards; use of a polymerase chain reaction as a diagnostic tool; ring-fencing of beds; and separate wound dressing rooms for each ward. The total cost is projected to be pound301,000.

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

Background

This study aimed to establish the feasibility and cost-effectiveness of rapid molecular screening for hospital-acquired meticillin-resistant Staphylococcus aureus (MRSA) in surgical patients within a teaching hospital.

Methods

In 2006, nasal swabs were obtained before surgery from all patients undergoing elective and emergency procedures, and screened for MRSA using a rapid molecular technique. MRSA-positive patients were started on suppression therapy of mupirocin nasal ointment (2 per cent) and undiluted chlorhexidine gluconate bodywash.

Results

A total of 18 810 samples were processed, of which 850 (4·5 per cent) were MRSA positive. In comparison to the annual mean for the preceding 6 years, MRSA bacteraemia fell by 38·5 per cent (P &lt; 0·001), and MRSA wound isolates fell by 12·7 per cent (P = 0·031). The reduction in MRSA bacteraemia and wound infection was equivalent to a saving of 3·78 beds per year (£276 220), compared with the annual mean for the preceding 6 years. The cost of screening was £302 500, making a net loss of £26 280. Compared with 2005, however, there was a net saving of £545 486.

Conclusion

Rapid MRSA screening of all surgical admissions resulted in a significant reduction in staphylococcal bacteraemia during the screening period, although a causal link cannot be established.

A study of the efficacy and cost-effectiveness of MRSA screening and monitoring on surgical wards using a new, rapid molecular test (EMMS)

BACKGROUND

MRSA is a significant contributor to prolonged hospital stay, poor clinical outcome and increased healthcare costs amongst surgical patients. A PCR test has been developed for rapid detection of MRSA in nasal swabs. The aims of this study are (1) to estimate the effectiveness of screening using this rapid PCR tests vs culture in reducing MRSA cross-infection rates; (2) to compare the cost of each testing strategy, including subsequent health care costs; and (3) to model different policies for the early identification and control of MRSA infection in surgical patients.

METHODS/DESIGN

The study is a prospective two-period cross-over study set in 7 surgical wards covering different surgical specialities. A total of 10,000 patients > 18 years will be tested over 16 months. The only difference between the two study periods is the method used for the detection of MRSA in each ward (rapid v conventional culture), with all other infection control practices remaining consistent between the arms. The study has been designed to complement routine practice in the NHS. Outcomes are MRSA cross-infection rates (primary outcome) and need for antibiotic therapy and MRSA-related morbidity. Parallel economic and modelling studies are being conducted to aid in the interpretation of the results and to evaluate the cost-effectiveness of the rapid PCR screening strategy.

DISCUSSION

This paper highlights the design, methods and operational aspects of a study evaluating rapid MRSA screening in the surgical ward setting.

[Using a 48-hour delay from admission to the first positive culture without any other consideration: an accurate method to differentiate acquired and imported methicillin-resistant Staphylococcus aureus?]

To differentiate imported and acquired strains of methicillin-resistant Staphylococcus aureus (MRSA), a 48-hour delay from hospital admission to the first MRSA-positive culture is usually considered. To assess if taking into account this delay without any other consideration is an accurate method, we defined 3 situations for whom we considered the MRSA acquisition status as questionable. The other situations were defined as either acquired MRSA or imported MRSA. We determined the acquisition status of MRSA (acquired, imported, or questionable) isolated during a 20-month period by considering or not considering screening samples performed on admission. The ratio "imported MRSA/acquired MRSA" (I/A) was calculated according to (1) the consideration of MRSA with questionable status as imported or acquired, and (2) the consideration of screening samples or not in the calculation of the ratio. The acquisition status in our hospital was questionable in 3.6% of patients when all samples were considered and in 12,0% when only clinical samples were taken into account (p = 0,01). The ratio I/A was 4-fold higher by considering both clinical and screening cultures and questionable status as imported than by considering only clinical samples and questionable status as acquired. Using a 48-hour delay without any other consideration is probably an accurate method to differentiate acquired and imported MRSA when a selective screening programme at admission in operational. Conversely, this definition seems to be more hazardous in the absence of screening.

Staphylococcus aureus colonization among nursing home residents in a large Finnish nursing home

We studied colonization with methicillin-resistant and -sensitive Staphylococcus aureus (MRSA, MSSA) in the second largest nursing home in Finland, in which the residents volunteered had their nostrils, throats, perineums, skin lesions, and catheter exit sites swabbed, and catheter urines cultured. The specimens were cultured onto non-selective and selective agar, with or without enrichment in salt-containing trypticase soy broth (TSB). S. aureus was identified by routine methods, methicillin resistance was detected by oxacillin and cefoxitin disk diffusion and MIC E-tests, and GenoType MRSA -test was used for mecA gene confirmation. A total of 663 cultures were obtained from 213 residents. Of those, 165 specimens (25%) from 94 residents (44%) were positive for S. aureus, and 3 specimens (0.4%) from 2 (0.9%) residents were positive for MRSA. Of the 165 S. aureus isolates, 31 (19%) from 25 (27%) residents were found only from sites other than nostrils (30 MSSA and 1 MRSA). TSB enrichment detected additional 33 (5%) S. aureus isolates (32 MSSA and 1 MRSA), resulting in 8 (5%) additional residents. None of the MRSA strains would have been found if only nostrils and throat had been screened, and no enrichment broth had been used.

Evaluation of a single-locus real-time polymerase chain reaction as a screening test for specific detection of methicillin-resistant Staphylococcus aureus in ICU patients

The aim of the present study was to determine the diagnostic value of a single-locus real-time polymerase chain reaction (PCR) recently proposed for rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) from clinical samples (IDI-MRSA; Infectio Diagnostic, Sainte-Foy, Québec, Canada). This test, which was developed on the basis of studies of the sequence analysis of the mecA gene carried by staphylococcal cassette chromosome mec (SCCmec), was used to screen nasal swabs of 320 intensive care unit (ICU) patients at admission. The results were compared with those of conventional culture of swabs from several body sites. When compared with culture of swabs from the nose, throat, and wounds, the diagnostic values of the real-time PCR test from nasal swabs were as follows: 92.3% sensitivity, 98.6% specificity, 75.0% positive predictive value, and 99.6% negative predictive value. Fifteen (4.7%) samples could not be evaluated because the PCR reaction was inhibited, even after the samples were frozen and thawed for retesting. Culture of nasal swabs showed that 78 of the patients were colonized with methicillin-susceptible S. aureus. Unexpectedly, 4 (5.1%) of these samples gave false-positive results in the IDI-MRSA. These isolates were all single clones, as shown by pulsed-field gel electrophoresis and spa typing. Reliable results were obtained with the IDI-MRSA assay, even in a patient population with a low prevalence (approximately 4%) of MRSA and even when compared with swabs of different body sites. Nevertheless, further work is needed to reduce the inhibition rate of the PCR and to explain why false-positive results were obtained with methicillin-susceptible S. aureus.

Controlling methicillin-resistant Staphylococcus aureus by stepwise implementation of preventive strategies in a university hospital: impact of a link-nurse system on the basis of multidisciplinary approaches

BACKGROUND

Current approaches in the control of methicillin-resistant Staphylococcus aureus (MRSA) in the large tertiary referral hospital have not been universally successful.

METHODS

The trend of MRSA rates and their relationship with stepwise implementation of preventive strategies in Tokai University Hospital during a 76-month period from September 1998 to December 2004, was retrospectively analyzed with a quasi-experimental design.

RESULTS

Implementation of strategies including a feedback process with case and epidemic reporting, an infection control team and office, and a preventive guideline for MRSA did not result in reduction in monthly MRSA rates in the hospital, as analyzed with Shewhart u charts. When infection control link nurses were organized and their activities became full-scale, there appeared significant reduction in arithmetic mean of the monthly rates of MRSA from 6.3% to 5.0% in June 2002. Meanwhile the mean values for monthly counts of new MRSA cases also dropped in 15 of 25 wards/units in June 2002, as analyzed with Exponentially Weighted Moving Average charts. Concurrently, there was a significant increase (17.3%) in the monthly consumption of handwashing liquid plain soap. Thereafter the MRSA rates remained low for 2 years within three standard deviations.

CONCLUSIONS

The sustained reduction of MRSA rates in the hospital can be related to introduction of the infection control link-nurse system on the basis of continuous enforcement of basic and multidisciplinary approaches such as hand-hygiene compliance.

An outbreak in an intensive care unit of a strain of methicillin-resistant Staphylococcus aureus sequence type 239 associated with an increased rate of vascular access device-related bacteremia

BACKGROUND

Patients in intensive care units are at high risk of developing methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. We report an epidemiological and bacterial genomic analysis of a 2-year outbreak in an intensive care unit of a variant of MRSA sequence type 239 (hereafter designated TW).

METHODS

A cohort study was conducted to compare risk factors for MRSA bacteremia in patients who acquired TW versus patients who acquired non-TW strains of MRSA. Genetic analysis of TW was performed using multilocus sequence typing and microarray analysis.

RESULTS

Patients who acquired TW were more likely than patients who acquired non-TW strains of MRSA to have MRSA isolated from blood samples (47% vs. 13%; P<.001) and to have MRSA-positive vascular access device-sample cultures (59% vs. 26%; P<.001), but less likely to have MRSA isolated from screening swab samples (30% vs. 71%; P<.001). This increased rate of TW bacteremia was confined to the first week after acquisition of TW infection. Using Cox regression analysis, the adjusted hazard ratio for bacteremia with TW was 4.5 times that of non-TW strains of MRSA (95% confidence interval, 2.25-9.00; P<.001). Microarray analysis revealed that TW had accumulated all detectable mobile genetic elements that were variably expressed by other epidemic strains of MRSA sequence type 239 in the United Kingdom.

CONCLUSIONS

To our knowledge, this is the first report to provide direct evidence that strains of MRSA can differ in their ability to cause bacteremia. Further genetic and in vitro analysis of the TW strain may provide insight into the mechanism of vascular access device-related bacteremia in the intensive care unit environment.

Community-acquired Staphylococcus aureus pneumonia accompanied by rapidly progressive glomerulonephritis and hemophagocytic syndrome

A 59-year-old woman without underlying disease was admitted to a local hospital because of lung abscess, cytopenias and renal failure. 3 days before admission, she was diagnosed as influenza infection and was under antiviral therapy. Blood cultures were positive for methicillin-sensitive Staphylococcus aureus (MSSA). She was transferred to our hospital on the 15th day at the local hospital because the clinical manifestations could not improve even though she was treated with multiple intravenous antibiotics directed against MSSA. Sputum cultures yielded methicillin-resistant S. aureus (MRSA) producing toxic shock syndrome toxin-1 (TSST-1) and serologic test indicated hypercytokinemia. She was diagnosed as rapidly progressive glomerulonephritis and hemophagocytic syndrome associated with staphylococcal infection. The pulmonary lesions, cytopenias and renal dysfunction improved as a result of long-term antimicrobial treatment including vancomycin, hemodialysis, short-term administration of corticosteroid and other supportive cares. She was finally weaned from hemodialysis on the 73rd hospital day. In recent years, the number of cases of S. aureus producing TSST-1 and enterotoxin has been increasing and in cases of staphylococcal infections, close attention should be given to toxin-mediated as well as non-toxin-mediated clinical manifestations.

Concurrent analysis of nose and groin swab specimens by the IDI-MRSA PCR assay is comparable to analysis by individual-specimen PCR and routine culture assays for detection of colonization by methicillin-resistant Staphylococcus aureus

The IDI-MRSA assay (Infectio Diagnostic, Inc., Sainte-Foy, Quebec, Canada) with the Smart Cycler II rapid DNA amplification system (Cepheid, Sunnyvale, CA) appears to be sensitive and specific for the rapid detection of nasal colonization by methicillin-resistant Staphylococcus aureus (MRSA). We assessed the sensitivity and specificity of this assay under conditions in which both the nose and cutaneous groin specimens were analyzed together and compared the accuracy of this PCR approach to that when these specimens were tested separately and by culture assays in an inpatient population with known high rates (12 to 15%) of MRSA colonization. Of 211 patients screened, 192 had results assessable by all three methods (agar-broth culture, separate nose and groin IDI-MRSA assay, and combined nose-groin IDI-MRSA assay), with MRSA carriage noted in 31/192 (16.1%), 41/192 (21.4%), and 36/192 (18.8%) patients by each method, respectively. Compared to agar culture results, the sensitivity and specificity of the combined nose-groin IDI-MRSA assay were 88.0% and 91.6%, respectively, whereas when each specimen was processed separately, the sensitivities were 90.0% (nose) and 83.3% (groin) and the specificities were 91.7% (nose) and 90.2% (groin). IDI-MRSA assay of a combined nose-groin specimen appears to have an accuracy similar to that of the current recommended PCR protocol, providing results in a clinically useful time frame, and may represent a more cost-effective approach to using this assay for screening for MRSA colonization.

Duration of methicillin-resistant Staphylococcus aureus carriage, according to risk factors for acquisition

OBJECTIVE

To examine the duration of methicillin-resistant Staphylococcus aureus (MRSA) carriage and its determinants and the influence of eradication regimens.

DESIGN

Retrospective cohort study.

SETTING

A 1,033-bed tertiary care university hospital in Bern, Switzerland, in which the prevalence of methicillin resistance among S. aureus isolates is less than 5%.

PATIENTS

A total of 116 patients with first-time MRSA detection identified at University Hospital Bern between January 1, 2000, and December 31, 2003, were followed up for a mean duration of 16.2 months.

RESULTS

Sixty-eight patients (58.6%) cleared colonization, with a median time to clearance of 7.4 months. Independent determinants for shorter carriage duration were the absence of any modifiable risk factor (receipt of antibiotics, use of an indwelling device, or presence of a skin lesion) (hazard ratio [HR], 0.20 [95% confidence interval {CI}, 0.09-0.42]), absence of immunosuppressive therapy (HR, 0.49 [95% CI, 0.23-1.02]), and hemodialysis (HR, 0.08 [95% CI, 0.01-0.66]) at the time MRSA was first MRSA detected and the administration of decolonization regimen in the absence of a modifiable risk factor (HR, 2.22 [95% CI, 1.36-3.64]). Failure of decolonization treatment was associated with the presence of risk factors at the time of treatment (P=.01). Intermittent screenings that were negative for MRSA were frequent (26% of patients), occurred early after first detection of MRSA (median, 31.5 days), and were associated with a lower probability of clearing colonization (HR, 0.34 [95% CI, 0.17-0.67]) and an increased risk of MRSA infection during follow-up.

CONCLUSIONS

Risk factors for MRSA acquisition should be carefully assessed in all MRSA carriers and should be included in infection control policies, such as the timing of decolonization treatment, the definition of MRSA clearance, and the decision of when to suspend isolation measures.

Evidence-based model for hand transmission during patient care and the role of improved practices

Hand cleansing is the primary action to reduce health-care-associated infection and cross-transmission of antimicrobial-resistant pathogens. Patient-to-patient transmission of pathogens via health-care workers' hands requires five sequential steps: (1) organisms are present on the patient's skin or have been shed onto fomites in the patient's immediate environment; (2) organisms must be transferred to health-care workers' hands; (3) organisms must be capable of surviving on health-care workers' hands for at least several minutes; (4) handwashing or hand antisepsis by the health-care worker must be inadequate or omitted entirely, or the agent used for hand hygiene inappropriate; and (5) the caregiver's contaminated hand(s) must come into direct contact with another patient or with a fomite in direct contact with the patient. We review the evidence supporting each of these steps and propose a dynamic model for hand hygiene research and education strategies, together with corresponding indications for hand hygiene during patient care.

Bayesian inference of hospital-acquired infectious diseases and control measures given imperfect surveillance data

This paper describes a stochastic epidemic model developed to infer transmission rates of asymptomatic communicable pathogens within a hospital ward. Inference is complicated by partial observation of the epidemic process and dependencies within the data. The epidemic process of nosocomial communicable pathogens can be partially observed by routine swabs testing for the presence of the pathogen. False-negative swab results must be accounted for and make it difficult to ascertain the number of patients who were colonized. Reversible jump Markov chain Monte Carlo methods are used within a Bayesian framework to make inferences about the colonization rates and unknown colonization times. The methods are applied to routinely collected data concerning methicillin-resistant Staphylococcus Aureus in an intensive care unit to estimate the effectiveness of isolation on reducing transmission of the bacterium.

Gentamicin-susceptible or gentamicin-resistant methicillin-resistant Staphylococcus aureus: a case-case study

Gentamicin-susceptible methicillin-resistant Staphylococcus aureus (GS-MRSA) strains are replacing gentamicin-resistant MRSA (GR-MRSA) strains. We showed that exposure to other patients harboring GS-MRSA was the major risk factor for GS-MRSA acquisition, and that antimicrobial exposure, especially to beta-lactams, was strongly associated with acquisition of GR-MRSA but not GS-MRSA. Gentamicin use was significantly associated with GR-MRSA acquisition in univariate analysis only.

Screening strategies in surveillance and control of methicillin-resistant Staphylococcus aureus (MRSA)

With reports of hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) continuing to increase and therapeutic options decrease, infection control methods are of increasing importance. Here we investigate the relationship between surveillance and infection control. Surveillance plays two roles with respect to control: it allows detection of infected/colonized individuals necessary for their removal from the general population, and it allows quantification of control success. We develop a stochastic model of MRSA transmission dynamics exploring the effects of two screening strategies in an epidemic setting: random and on admission. We consider both hospital and community populations and include control and surveillance in a single framework. Random screening was more efficient at hospital surveillance and allowed nosocomial control, which also prevented epidemic behaviour in the community. Therefore, random screening was the more effective control strategy for both the hospital and community populations in this setting. Surveillance strategies have significant impact on both ascertainment of infection prevalence and its control.

Risk factors for Staphylococcus aureus nasal carriage in residents of three nursing homes in Germany

The prevalence of Staphylococcus aureus nasal carriage in three nursing homes (N=500) was 36.6%. No meticillin-resistant S. aureus (MRSA) was detected. The following significant risk factors for S. aureus nasal carriage were identified: vascular cognitive impairment [odds ratio (OR)=0.31]; diabetes mellitus (OR=1.82); hypertension (OR=0.30); chronic obstructive pulmonary disease (OR=1.86); stroke (OR=3.31); antibiotic therapy within the previous three months (OR=2.10); and level 2 care (defined as highly dependent, needing help in activities of daily living for up to 4h/day) (OR=1.97). Compared with other countries, the prevalence of MRSA nasal carriage in residents of German nursing homes is low.

Consideration of age at admission for selective screening to identify methicillin-resistant Staphylococcus aureus carriers to control dissemination in a medical ward

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has become an increasingly important pathogen responsible for hospital-acquired infections. Our study was to evaluate the efficiency of our selective screening program for methicillin-resistant Staphylococcus aureus (MRSA) carriers at admission to nonintensive care units.

METHODS

During 6 months, all patients were screened at admission to an internal medicine ward, at which time they were classified as patients at risk of carriage (PRC) and those with no known risk factor. The amplitude of cross transmission was estimated using various indicators during this universal screening period and during the same calendar period of the preceding year (selective screening).

RESULTS

The prevalence of MRSA carriage at admission was 5.5%. Among the 22 carriers identified, only 10 were PRC. Age >80 years was significantly associated with MRSA carriage upon admission (OR, 3.5; P < .01). All estimation indicators of MRSA dissemination amplitude were significantly lower during universal screening (relative risks varied from 2.79 to 26.4 according to indicators), demonstrating the need to broaden our criteria defining PRC.

CONCLUSION

Adding patients >80 years of age to our PRC definition would increase screening sensitivity (15 carriers identified for 128 patients sampled) and would enable early implementation of barrier precautions for the additional carriers identified.

Use of surveillance cultures and enteral vancomycin to control methicillin-resistant Staphylococcus aureus in a paediatric intensive care unit

This study assessed the effects of throat and gut surveillance, combined with enteral vancomycin, on gut overgrowth, transmission of methicillin-resistant Staphylococcus aureus (MRSA), infections and mortality in patients admitted to a paediatric intensive care unit (PICU). A 4-year prospective observational study was undertaken with 1241 children who required ventilation for >or=4 days. Patients identified as MRSA carriers following surveillance cultures of throat and rectum received enteral vancomycin. Twenty-nine (2.4%) children carried MRSA, 19 on admission and nine during treatment in the PICU; one patient was not able to be evaluated. Overgrowth was present in 22 (75%) of the carriers. Ten (0.8%) children developed 21 MRSA infections (15 exogenous infections in eight children at a median of 8 days (IQR 3-10.5); five primary endogenous infections at a median of 3 days (IQR 1-25) in three children when they were in overgrowth status; one child developed both types of infection). Enteral vancomycin reduced gut overgrowth significantly, completely preventing secondary endogenous infections. Transmission occurred on nine occasions over a period of 4 years. Four patients died, two (5.9%) with MRSA infection, giving a mortality (11.8%) similar to the study population (9.8%). No emergence of vancomycin-resistant enterococci or S. aureus with intermediate susceptibility to vancomycin was detected. A policy based on throat and gut surveillance, combined with enteral vancomycin, for critically-ill children who were MRSA carriers was found to be effective and safe, and challenges the recommended guidelines of nasal swabbing followed by topical mupirocin.

Evaluation of a Strategy of Screening Multiple Anatomical Sites for Methicillin-Resistant Staphylococcus aureus at Admission to a Teaching Hospital

We compared the sensitivity of screening with nasal culture alone with that of a multiple-site screening method for the identification of carriers of methicillin-resistant Staphylococcus aureus at hospital admission. If nasal cultures alone had been used during the 1-year study, 27.0% of carriers of methicillin-resistant S. aureus would have been missed, which corresponds to 560 theoretical isolation days. If rectal screening had not been used, 431 theoretical isolation days would have been missed, and, if axillary screening had not been used, 99 theoretical isolation days would have been missed.

Risk factors for ICU-acquired methicillin-resistant Staphylococcus aureus infections

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen that causes severe morbidity and mortality in many hospitals worldwide, and MRSA infections are frequent in intensive care units (ICUs).

OBJECTIVE

A prospective study was implemented to investigate the risk factors for ICU-acquired MRSA infections.

METHODS

This study was conducted in surgical and neurologic ICUs from May to November 2003. The patients staying in ICUs more than 48 hours were included in the study. All of the patients were visited daily, and data were recorded on individual forms for each patient until discharge or death. Nasal swab cultures were done within 48 hours of ICU admission and repeated every week until the patients colonized with MRSA or were discharged from ICUs. ICU-acquired MRSA infection was diagnosed when MRSA was isolated from the infected site.

RESULTS

Overall, 249 patients were followed during the study. MRSA infection was detected in 21 (8.4%) of these patients. The most frequent infection was primary bloodstream infection (10/21, 47%). It was followed by pneumonia (8/21, 38%) and surgical site infection (3/21, 14%). Nasal MRSA colonization was detected in 59 (23.7%) patients, and 12 of them (20.3%) developed MRSA infection. In univariate analysis, hospitalization period in an ICU, intraabdominal and orthopedic pathologies, mechanical ventilation, central venous catheter insertion, total parenteral nutrition, previous antibiotic use, surgical ICU stay, nasal MRSA colonization, and presence of more than 2 patients having nasal colonization in the same ICU at the same time were found significant for MRSA infections. In multivariate analysis; hospitalization period in an ICU (OR, 1.090; 95% CI: 1.038-1.144, P = .001), central venous catheter insertion (OR, 1.822; 95% CI: 1.095-3.033, P = .021), previous antibiotic use (OR, 2.337; 95% CI: 1.326-4.119, P = .003) and presence of more than 2 patients having nasal colonization in the same ICU at the same time (OR, 1.398; 95% CI: 1.020-1.917, P = .037) were independently associated with MRSA infections.

CONCLUSION

According to the our results, hospitalization period in an ICU, presence of patients colonized with MRSA in the same ICU at the same time, previous antibiotic use, and central venous catheter insertion are independent risk factors for ICU-acquired MRSA infections. Detection of these factors helps to decrease the rate of MRSA infections in the ICUs.

The throat: an important site for MRSA colonization

In order to evaluate the value of bacterial cultures taken from the throat, 266 patients with MRSA were retrospectively assessed. At the time when MRSA was first detected in the patient, the most frequent sites positive for MRSA were a skin lesion (110 patients, 41%), the anterior nares (109 patients, 41%), and the throat (102 patients, 38%). In 26%, 17%, and 17% of the patients, a skin lesion, the anterior nares, and the throat, respectively, were the only site where MRSA was seen. In 123 patients cultured for MRSA because of a close contact with an already known MRSA patient, 65 patients (53%) were positive for MRSA in their throat and in 40 patients (33%), throat was the only sample site with MRSA at the time when the patient was found to be MRSA positive. 146 of the 266 patients (55%) were colonized with MRSA in the throat any time throughout the period they were MRSA positive. We conclude that throat is an important reservoir for MRSA and that samples taken from the throat should be included in screening patients for MRSA.

Bacteriophage lytic enzymes: novel anti-infectives

Bacteriophage lytic enzymes, or lysins, are highly evolved molecules produced by bacterial viruses (bacteriophage) to digest the bacterial cell wall for bacteriophage progeny release. Small quantities of purified recombinant lysin added to gram-positive bacteria causes immediate lysis resulting in log-fold death of the target bacterium. Lysins have now been used successfully in animal models to control pathogenic antibiotic resistant bacteria found on mucosal surfaces and in blood. The advantages over antibiotics are their specificity for the pathogen without disturbing the normal flora, the low chance of bacterial resistance to lysins and their ability to kill colonizing pathogens on mucosal surfaces, capabilities that were previously unavailable. Thus, lysins could be an effective anti-infective in an age of mounting antibiotic resistance.

Control of imported and acquired methicillin-resistant Staphylococcus aureus (MRSA) in mechanically ventilated patients: a dose-response study of enteral vancomycin to reduce absolute carriage and infection

This study aimed to quantify the animate source provided by the patients using the concept of "absolute carriage" by multiplying the carrier rate by the level of carriage; and to compare the impact of a low and high dose of an oropharyngeal vancomycin gel on the absolute MRSA carriage and infection. In all, 265 patients were included, 126 were MRSA positive. Fifty-five patients received 2% vancomycin gel during the first year whilst 4% vancomycin gel was given to 50 patients during the second year. Surveillance swabs of throat and rectum were obtained from all eligible patients on admission and then twice weekly. The vancomycin protocol was started as soon as the surveillance cultures were positive for MRSA. Those patients received one gram of enteral vancomycin daily, divided into four doses. During the first year 2% vancomycin gel 4 ml (80 mg) was applied in the oropharynx in four doses in addition to the enteral solution (Group A). During the second year 4% vancomycin gel 4 ml (160 mg) was used (Group B). The absolute carriage was high during both periods: 3.6 for Group A, and 3.2 for Group B. The 4% vancomycin protocol significantly reduced the absolute carriage, compared to the 2% vancomycin protocol: 2.6 versus 1.5 (P < 0.01). Significant reduction in secondary endogenous infections was found in the second year: seven versus 15 patients (P < 0.05). A total of 3,588 microbiological samples were processed. Neither Staphylococcus aureus with intermediate sensitivity to vancomycin (VISA) nor vancomycin-resistant enterococci (VRE) were detected.

Successful long-term program for controlling methicillin-resistant Staphylococcus aureus in intensive care units

OBJECTIVE

To evaluate the effectiveness of screening strategy and contact precautions for patients with methicillin-resistant Staphylococcus aureus (MRSA).

DESIGN AND SETTING

Prospective observational cohort from 1 February 1995 to 31 December 2001 in three intensive care units (45 beds) in a French teaching hospital.

PATIENTS

8,548 patients admitted to the three ICUs had nasal screening on ICU admission and weekly thereafter. Contact precautions were used in MRSA-positive patients. The following variables were collected: age, gender, severity score, length of stay, workload, and colonization pressure (percentage of patient-days with an MRSA to the number of patient-days in the unit). Alcohol-based handrub solution was introduced in July 2000. We compared the period before this (P1) with that thereafter (P2).

RESULTS

Of the 8,548 admitted patients 554 (6.5%) had MRSA at ICU admission, and 456 of the 7,515 (6.1%) exposed patients acquired MRSA. Acquisition incidence decreased from 7.0% in P1 to 2.8% in P2. Independent variables associated with MRSA acquisition were: age (adjusted odds ratio 1.013), severity score (1.047), length of ICU stay (1.015), colonization pressure (1.019), medical ICU (1.58), and P2 (0.49).

CONCLUSIONS

MRSA control in these ICUs characterized by a high prevalence of MRSA at admission was achieved via multiple factors, including screening, contact precautions, and use of alcoholic handrub solution. Our results after adjustment of risk factors for MRSA acquisition and the steady improvement in MRSA over several years strengthen these findings. MRSA spreading can be successfully controlled in ICUs with high colonization pressure.

Effectiveness of a hospital-wide selective screening programme for methicillin-resistant Staphylococcus aureus (MRSA) carriers at hospital admission to prevent hospital-acquired MRSA infections

Screening of potential MRSA-positive patients at hospital admission is recommended in German and international guidelines. This policy has been shown to be effective in reducing the frequency of nosocomial MRSA transmissions in the event of an outbreak, but the influence of screening on reducing hospital-acquired MRSA infections in a hospital setting where MRSA is endemic is not yet well-documented. This study describes the effect of hospital-wide screening of defined risk groups in a 700-bed acute care hospital during a period of 19 months. In a cohort study with a 19-month control period, the frequencies of hospital-acquired MRSA infections were compared with and without screening. In the control period, there were 119 MRSA-positive patients, of whom 48 had a hospital-acquired MRSA infection. On the basis of this frequency, a predicted total of 73.2 hospital-acquired MRSA infections was calculated for the screening period, but only 52% of the expected number (38 hospital-acquired MRSA infections) were observed, i.e., 48% of the predicted number of hospital-acquired MRSA infections were prevented by the screening programme. The screening programme was performed with minimal effort and can therefore be recommended as an effective measure to help prevent hospital-acquired MRSA infections.

Impact of screening for MRSA carriers at hospital admission on risk-adjusted indicators according to the imported MRSA colonization pressure

We evaluated the impact of the different components of a screening programme of methicillin-resistant Staphylococcus aureus (MRSA) carriers at hospital admission on the value of two risk-adjusted rates: the proportion of imported MRSA and an indicator of the MRSA colonization pressure (ICP), and the incidence of MRSA acquired and detected in our hospital. Indicators were calculated: (1) with no screening programme; (2) with a programme limited to the intensive care unit (ICU); (3) with a programme extended to patients with risk factors for MRSA carriage hospitalized in non-ICU wards. The programme included an automatic alert. Systematic sampling of patients with risk factors hospitalized in non-ICU settings detected nearly 50% of carriers at admission. The proportion of MRSA imported into our hospital varied from 35.4% without any screening programme to 71.8% when all components of our screening programme were considered (P<10(-4)). The ICP varied from 3.1% (31/985) with the complete programme to 10.4% (31/297) without any screening programme (P<10(-6)). Screening patients with risk factors for MRSA carriage hospitalized in non-ICU wards resulted in a 51% increase of the calculated proportion of imported strains and a 58% decrease of the ICP. The two studied indicators were strongly dependent on the screening strategy for MRSA carriers implemented at admission. The screening strategy for patients admitted to non-ICU wards who have risk factors for MRSA carriage seems to be the determinant for the interpretation of certain risk-adjusted indicators of MRSA cross-transmission. Comparisons of these indicators must consider the setting in which the screening programmes are implemented.

[Impact of nasal colonization by methicillin-resistant Staphylococcus aureus among geriatric intermediate care facility patients]

OBJECTIVE

To evaluate the impact of nasal carriage of Methicillin Resistant Staphylococcus aureus (MRSA) on antibiotic cost, infection morbidity, mortality and length of stay in a geriatric population.

METHODS

341 consecutive elderly patients (mean age 83.4 +/- 8.7 years) admitted to an intermediate care facility were prospectively include between November 1998 and October 1999. Nasal swab cultures were taken on admission.

RESULTS

In sixty patients (17.6%) no nasal swab was taken. Among the 281 patients screened, 52 were identified as MRSA carriers. The principle predictive factors were: diabetes (p=0,046), sores (p=0,03), malnutrition (p=0,02), polypathology (p=0,02) and prolongation of previous hospitalisation (p=0,09).

CONCLUSION

Nasal carriage of MRSA on admission to the facility was not a deleterious prognostic factor regarding duration of stay, infectious morbidity and antibiotic cost, but was associated with higher mortality risk.

Detection of methicillin-resistant Staphylococcus aureus directly from nasal swab specimens by a real-time PCR assay

Screening for colonization with methicillin-resistant Staphylococcus aureus (MRSA) is a key aspect of infection control to limit the nosocomial spread of this organism. Current methods for the detection of MRSA in clinical microbiology laboratories, including molecularly based techniques, require a culture step and the isolation of pure colonies that result in a minimum of 20 to 24 h until a result is known. We describe a qualitative in vitro diagnostic test for the rapid detection of MRSA directly from nasal swab specimens (IDI-MRSA; Infectio Diagnostic, Inc., Sainte-Foy, Quebec, Canada), based upon a real-time PCR and direct detection of MRSA via amplicon hybridization with a fluorogenic target-specific molecular beacon probe. Samples from 288 patients were analyzed for the presence of MRSA with the IDI-MRSA assay, compared to detection by either direct plating or enrichment broth selective culture methods. The diagnostic values for this MRSA screening method were 91.7% sensitivity, 93.5% specificity, 82.5% positive predictive value, and 97.1% negative predictive value when compared to culture-based methods. The time from the start of processing of specimen to result was approximately 1.5 h. In our hands, the IDI-MRSA assay is a sensitive and specific test for detection of nasal colonization with MRSA and providing for same-day results, allowing more efficient and effective use of infection control resources to control MRSA in health care facilities.