New threats to the control of methicillin-resistant Staphylococcus aureus

Bed occupancy rates and hospital-acquired Clostridium difficile infection: a cohort study

BACKGROUND

An emergent strain (ribotype 027) of Clostridium difficile infection (CDI) has been implicated in epidemics worldwide. Organizational factors such as bed occupancy have been associated with an increased incidence of CDI; however, the data are sparse, and the association has not been widely demonstrated. We investigated the association of bed occupancy and CDI within a large hospital organization in the United Kingdom.

OBJECTIVE

To establish whether bed occupancy rates are a significant risk factor for CDI in the general ward setting.

METHODS

A retrospective cohort study was carried out on data from 2006 to 2008. Univariate and multivariate Cox regression modeling was used to examine the strength and significance of the associations. Variables included patient characteristics, antibiotic policy exposure, case mix, and bed occupancy rates.

RESULTS

A total of 1,589 cases of hospital-acquired CDI were diagnosed (1.7% of admissions), with an overall infection rate of 2.16 per 1,000 patient-days. Median bed occupancy was 93.3% (interquartile range, 83.3%-100%) Univariate and multivariate analyses showed positive and statistically significant associations. In the adjusted model, patients on wards with occupancy rates of 80%-89.9% had rates of CDI that were 56% higher (hazard ratio, 1.56 [95% confidence interval, 1.18-2.04]; P < .001) compared with baseline (0%-69.9% occupancy). CDI rates were 55% higher for patients on wards with maximal bed occupancy (100%).

CONCLUSIONS

There is strong evidence of an association between high bed occupancy and CDI. Without effective interventions at high levels of bed occupancy, the economic benefits sought from reducing bed numbers may be negated by the increased risk of CDI.

Quantifying type-specific reproduction numbers for nosocomial pathogens: evidence for heightened transmission of an Asian sequence type 239 MRSA clone

An important determinant of a pathogen's success is the rate at which it is transmitted from infected to susceptible hosts. Although there are anecdotal reports that methicillin-resistant Staphylococcus aureus (MRSA) clones vary in their transmissibility in hospital settings, attempts to quantify such variation are lacking for common subtypes, as are methods for addressing this question using routinely-collected MRSA screening data in endemic settings. Here we present a method to quantify the time-varying transmissibility of different subtypes of common bacterial nosocomial pathogens using routine surveillance data. The method adapts approaches for estimating reproduction numbers based on the probabilistic reconstruction of epidemic trees, but uses relative hazards rather than serial intervals to assign probabilities to different sources for observed transmission events. The method is applied to data collected as part of a retrospective observational study of a concurrent MRSA outbreak in the United Kingdom with dominant endemic MRSA clones (ST22 and ST36) and an Asian ST239 MRSA strain (ST239-TW) in two linked adult intensive care units, and compared with an approach based on a fully parametric transmission model. The results provide support for the hypothesis that the clones responded differently to an infection control measure based on the use of topical antiseptics, which was more effective at reducing transmission of endemic clones. They also suggest that in one of the two ICUs patients colonized or infected with the ST239-TW MRSA clone had consistently higher risks of transmitting MRSA to patients free of MRSA. These findings represent some of the first quantitative evidence of enhanced transmissibility of a pandemic MRSA lineage, and highlight the potential value of tailoring hospital infection control measures to specific pathogen subtypes.

Eradication of an epidemic methicillin-resistant Staphylococcus aureus (MRSA) from a geriatric university hospital: evidence from a 10-year follow-up

We report on a successful eradication of methicillin-resistant S. aureus (MRSA) after an epidemic in 1992 in the geriatric ward of a tertiary-care hospital. After identification of MRSA in seven patients, all patients and staff members in the geriatric ward underwent screening. A multifaceted intervention plan was implemented: contact isolation, optimization of infection control and decolonization of all MRSA carriers. Thirty-two patients and five staff members were found to be MRSA carriers. Twenty one of 32 (66%) patients and all five staff members were successfully decolonized. Seven of 32 (22%) patients died during the epidemic before decolonization. A couple was discharged with persisting MRSA colonization and two individuals were lost to follow-up. The eradication of the epidemic clone was proven by systematic screenings in 1995 and 1997. Since then, the strain has no longer been identified in our institution, based on epidemiological surveillance and molecular typing of all MRSA strains obtained from any specimen. This study provides strong evidence that long-term eradication of an MRSA epidemic in a hospital is feasible, and endemicity of MRSA after an outbreak can be avoided. The successful bundle approach for eradication of MRSA during an epidemic is expensive, but the long-term benefits likely outweigh the initial heavy use of resources.

Recommendations for the prevention and control of methicillin-resistant Staphylococcus aureus isolates (MRSA) in hospitals and other healthcare facilities

The Commission for Hospital Hygiene and Infection Control (KRINKO) at the Robert Koch-Institute Berlin published the "Recommendations for Preventing and Controlling Methicillin-Resistant Staphylococcus aureus (MRSA) Strains in Hospitals and Other Medical Facilities" in the Federal Health Gazette in 1999 [1]. These recommendations were translated for the current edition of GMS Krankenhaushygiene Interdisziplinär by the German Society of Hospital Hygiene.KRINKO's work is legitimated by section sign 23 para. 2 of the Infection Protection Act. Regarding the legal nature of the KRINKO recommendations, it should be noted that they are neither a formal act or an administrative regulation. The KRINKO recommendations are instead an evidence-based consensus of particularly qualified experts. The consensus is reached by including the Federal States' authorities and all competent professional bodies and associations. This is to guarantee that the KRINKO recommendations reflect the state-of-the-art of medical science, and are met with a high degree of user acceptance. The recommendations are published in the Federal Health Gazette and on the RKI's Internet pages (http://www.rki.de/).Link to the German original edition of the MRSA recommendations.

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.

Overcrowding and understaffing in modern health-care systems: key determinants in meticillin-resistant Staphylococcus aureus transmission

Recent decades have seen the global emergence of meticillin-resistant Staphylococcus aureus (MRSA), causing substantial health and economic burdens on patients and health-care systems. This epidemic has occurred at the same time that policies promoting higher patient throughput in hospitals have led to many services operating at, or near, full capacity. A result has been limited ability to scale services according to fluctuations in patient admissions and available staff, and hospital overcrowding and understaffing. Overcrowding and understaffing lead to failure of MRSA control programmes via decreased health-care worker hand-hygiene compliance, increased movement of patients and staff between hospital wards, decreased levels of cohorting, and overburdening of screening and isolation facilities. In turn, a high MRSA incidence leads to increased inpatient length of stay and bed blocking, exacerbating overcrowding and leading to a vicious cycle characterised by further infection control failure. Future decision making should use epidemiological and economic evidence to evaluate the effect of systems changes on the incidence of MRSA infection and other adverse events.

MRSA and the environment: implications for comprehensive control measures

Environmental contamination with methicillin-resistant Staphylococcus aureus (MRSA) is established soon after colonized or infected patients become resident. There are many studies that detail the mechanisms of spread and environmental survival of methicillin-susceptible Staphylococcus aureus (MSSA); this knowledge translates directly into the same findings for MRSA. The potential ubiquity of MRSA in a health-care setting poses challenges for decontamination. Whereas patients and medical staff are important sources for MRSA spread, the environmental burden may contribute significantly in various contexts. Effective control measures must therefore include consideration for MRSA in the environment.

Development and validation of measures to assess prevention and control of AMR in hospitals

BACKGROUND

The rapid spread of antimicrobial resistance (AMR) in the US hospitals poses serious quality and safety problems. Expert panels, identifying strategies for optimizing antibiotic use and preventing AMR spread, have recommended hospitals undertake efforts to implement specific evidence-based practices.

OBJECTIVE

To develop and validate a measurement scale for assessing hospitals' efforts to implement recommended AMR prevention and control measures.

STUDY DESIGN

Surveys were mailed to infection control professionals in a national sample of 670 US hospitals stratified by geographic region, bedsize, teaching status, and VA affiliation.

SUBJECTS

: Four hundred forty-eight infection control professionals participated (67% response rate).

METHODS

Survey items measured implementation of guideline recommendations, practices for AMR monitoring and feedback, AMR-related outcomes (methicillin-resistant Staphylococcus aureus prevalence and outbreaks [MRSA]), and organizational features. "Derivation" and "validation" samples were randomly selected. Exploratory factor analysis was performed to identify factors underlying AMR prevention and control efforts. Multiple methods were used for validation.

RESULTS

We identified 4 empirically distinct factors in AMR prevention and control: (1) practices for antimicrobial prescription/use, (2) information/resources for AMR control, (3) practices for isolating infected patients, and (4) organizational support for infection control policies. The Prevention and Control of Antimicrobial Resistance scale was reliable and had content and construct validity. MRSA prevalence was significantly lower in hospitals with higher resource/information availability and broader organizational support.

CONCLUSIONS

The Prevention and Control of Antimicrobial Resistance scale offers a simple yet discriminating assessment of AMR prevention and control efforts. Use should complement assessment methods based exclusively on AMR outcomes.

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.

Control and Outcome of a Large Outbreak of Colonization and Infection with Glycopeptide-Intermediate Staphylococcus aureus in an Intensive Care Unit

BACKGROUND

Glycopeptide-intermediate Staphylococcus aureus (GISA) is emerging as a cause of nosocomial infection and outbreaks of infection and colonization in intensive care units (ICUs). We describe an outbreak of GISA colonization/infection and the ensuing control measures in an ICU and investigate outcomes of the affected patients.

METHODS

We describe an outbreak of GISA colonization and infection that affected 21 patients in a medical ICU at a tertiary care teaching hospital, as well as the measures taken to eradicate the GISA strain.

RESULT

Recognition of the outbreak was difficult. Infections, all of which were severe, were diagnosed in 11 of 21 patients. Patient isolation and barrier precautions failed when used alone. Addition of a stringent policy of restricted admissions, twice daily environmental cleaning, and implementation of hand decontamination with a hydroalcoholic solution led to outbreak termination. This was associated with increases in workload, despite a marked decrease in the number of admissions.

CONCLUSION

This first description of a large outbreak of GISA colonization and infection underlines the importance of routine GISA-strain detection when methicillin-resistant S. aureus is isolated. Outbreak control may be difficult to achieve.

Implementation of strategies to prevent and control the emergence and spread of antimicrobial-resistant microorganisms in U.S. hospitals

OBJECTIVE

To examine the extent to which the strategies recommended by the National Foundation for Infectious Diseases (NFID)-Centers for Disease Control and Prevention (CDC) co-sponsored workshop, Antimicrobial Resistance in Hospitals: Strategies to Improve Antimicrobial Use and Prevent Nosocomial Transmission of Antimicrobial-Resistant Microorganisms, have been implemented and the relationship between the degree of implementation and hospital culture, leadership, and organizational factors.

DESIGN

Survey.

SETTING

A representative sample of U.S. hospitals stratified by teaching status, bed size, and geographic region.

PARTICIPANTS

Infection control professionals.

RESULTS

Surveyed hospitals had implemented strategies to optimize the use of antimicrobials and to detect, report, and prevent transmission of antimicrobial-resistant microorganisms. Multivariate analyses found that hospitals with a greater degree of implementation of the NFID-CDC strategic goals were more likely to have management support, education of staff, and interdisciplinary groups specifically to address these issues; they were also more likely to engage in benchmarking on broader quality of care indicators.

CONCLUSIONS

Most surveyed hospitals had implemented some measures to address the NFID-CDC recommendations; however, hospitals need to do much more to improve antimicrobial use and to increase their efforts to detect, report, and control the spread of antimicrobial resistance. A supportive hospital administration must foster a culture of ongoing support, education, and interdisciplinary work groups focused on this important issue to successfully accomplish these goals.

Methicillin-resistant Staphylococcus aureus in horses and horse personnel, 2000-2002

Methicillin-resistant Staphylococcus aureus was isolated from horses and horse personnel in a pattern suggestive of interspecies transmission of a human-origin clone.

Methicillin-resistant Staphylococcus aureus (MRSA) infection was identified in 2 horses treated at a veterinary hospital in 2000, prompting a study of colonization rates of horses and associated persons. Seventy-nine horses and 27 persons colonized or infected with MRSA were identified from October 2000 to November 2002; most isolations occurred in a 3-month period in 2002. Twenty-seven (34%) of the equine isolates were from the veterinary hospital, while 41 (51%) were from 1 thoroughbred farm in Ontario. Seventeen (63%) of 27 human isolates were from the veterinary hospital, and 8 (30%) were from the thoroughbred farm. Thirteen (16%) horses and 1 (4%) person were clinically infected. Ninety-six percent of equine and 93% of human isolates were subtypes of Canadian epidemic MRSA-5, spa type 7 and possessed SCCmecIV. All tested isolates from clinical infections were negative for the Panton-Valentine leukocidin genes. Equine MRSA infection may be an important emerging zoonotic and veterinary disease.

Antibiotic susceptibility of bacteria most commonly isolated from bone related infections: the role of cephalosporins in antimicrobial therapy

Bone infections, which can be acute or chronic, often require aggressive antibiotic therapy, whether treated at home or in the community. Surveillance programmes are essential tools in the monitoring of antimicrobial resistance and can act as a resource to maintain effective prescribing. The Surveillance Network (TSN), which collects organism and patient-specific data from a network of laboratories across the United States, was used to analyse susceptibility of common bacterial species isolated from bone infections during 2000-2002. Narrow-spectrum antimicrobials such as vancomycin, quinupristin-dalfopristin and linezolid demonstrated good activity against Staphylococcus aureus and streptococci, and were active against 100% of isolates. However, Gram-negative species were also commonly isolated from these sites of infection. Later-generation cephalosporins, represented by ceftriaxone, cefotaxime and cefepime, exhibited a broad spectrum of activity including Enterobacteriaceae, streptococci and methicillin-susceptible S. aureus, but they were not active against methicillin-resistant S. aureus (MRSA) and showed variable activity against Pseudomonas aeruginosa. Using ceftazidime as a marker for extended spectrum beta-lactamase (ESBL) expression, less than 3% of Escherichia coli or Klebsiella pneumoniae expressed this phenotype. Based on current in vitro activity, the third-generation cephalosporins provide broad-spectrum coverage useful for the empirical therapy of suspected bone infections, especially for patients treated in the community or hospitalised with community-acquired infections.

Clonal spread of methicillin-resistant Staphylococcus aureus in a large geographic area of the United States

Methicillin resistance in Staphylococcus aureus has rapidly increased over the last two decades. This increase is paralleled by the emergence of unique multi-resistant MRSA clones. In Brazil, Argentina, Uruguay, Portugal and Czech Republic a specific MRSA clone is widely spread, the so-called Brazilian epidemic clone. Another epidemic clone, the Iberian clone, is disseminated in Spain, Portugal, Belgium, Scotland, Italy, Germany and New York. Thus, a large number of hospital-acquired infections have been caused by specific MRSA clones. Using different molecular techniques for MRSA typing, we verified that two unique epidemic clones are spread over large geographic area in the US. In addition, we showed that a previously described MRSA clone type, the New York clone (I::A:A), is widely spread beyond the New York frontiers.

The impact of methicillin-resistant Staphylococcus aureus in a neurosurgical unit: a growing problem

OBJECT

Methicillin-resistant Staphylococcus aureus (MRSA) infection is a growing problem worldwide. To investigate the severity of the problem, the authors surveyed the incidence of MRSA colonization and infection in the neurosurgical unit at their institution.

METHODS

Patients colonized or infected with MRSA who had been treated in the neurosurgical unit between 1993 and 1999 were retrospectively identified from laboratory records. There were 203 patients with MRSA-positive cultures, and the incidence of infection increased between 1993 (16 cases; 1.9% of admissions) and 1999 (60 cases; 6.7% of admissions). The mean duration of hospital stay was longer in patients with MRSA than in all patients treated in the unit (33.6 compared with 10.3 days, p < 0.001). Methicillin-resistant S. aureus was isolated from the nose in 89 patients, the throat in 79, the perineum in 52, surgical wounds in 16, sputum in 15, blood in 10, and from multiple sites in 69 patients. Fifty-six patients (28%) were infected with MRSA, and there were 15 deaths, of which three (20%) were likely to be due to the infection. The sources of MRSA included the neurosurgical ward in 84 patients, the intensive care unit in 28, other hospitals in 39, and the community in 17. The common strains of MRSA isolated were epidemic (E)MRSA- 16 (110 cases) and EMRSA-15 (31 cases). The microorganism was eradicated in 16 cases, not eradicated in 20, and 167 patients were discharged from the hospital before eradication was achieved. All MRSA isolates were sensitive to vancomycin and teicoplanin and there was reduced sensitivity to mupirocin.

CONCLUSIONS

Infection with MRSA is a growing problem in the neurosurgical population, and most cases are hospital-acquired and are associated with longer hospital stays. Asymptomatic colonization by this organism is far more common than infection of the surgical wound, although there is still morbidity due to MRSA sepsis. Most patients with MRSA are discharged before eradication of infection is achieved, thus increasing the risk that the infection will spread in the community. Strict adherence to the basic principles of infection control is the key to eradication of MRSA.

Cost-effectiveness of active surveillance cultures and contact/droplet precautions for control of methicillin-resistant Staphylococcus aureus

Some have reported that adopting Centers for Disease Control and Prevention guidelines requiring contact precautions for methicillin-resistant Staphylococcus aureus (MRSA) had no impact on rates of nosocomial spread or infection, and may therefore waste money. The objective of the present study was to evaluate the cost-effectiveness of active surveillance cultures and barrier precautions for controlling MRSA. Estimated costs of surveillance cultures and isolation measures used during an MRSA outbreak at this hospital were compared with the estimated attributable excess costs of methicillin resistance (i.e., the difference between MRSA and methicillin-sensitive S. aureus costs) for bacteraemias occurring during an MRSA outbreak not promptly controlled at another hospital. The study was set in the neonatal intensive care units of two tertiary care hospitals. Estimated costs of controlling the 10.5-month outbreak in this neonatal intensive care unit that resulted in 18 colonized and four infected infants ranged from $48 617 to $68 637. The estimated attributable excess cost of 75 MRSA bacteraemias in a second neonatal intensive care unit outbreak that resulted in 14 deaths and lasted 51 months was $1 306 600. Weekly active surveillance cultures and isolation of patients with MRSA halted an outbreak at this hospital, and cost 19- to 27-fold less than the attributable costs of MRSA bacteraemias in another outbreak that was not promptly controlled. The costs of infections at other body sites and the human cost of deaths from infection were not estimated but would further help to justify the cost of identifying colonized patients and implementing effective preventive measures.

Spread of methicillin-resistant Staphylococcus aureus in a neonatal intensive unit associated with understaffing, overcrowding and mixing of patients

Over the period May-June 1999, an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) was registered in eight newborns in a neonatal intensive care unit (NICU) at the Department of Pediatrics, Ullevål University Hospital (UUH) in Oslo. Seven were infected or colonized with an indistinguishable strain, detected at the NICU, and one patient with a slightly different PFGE type (i.e. a subtype) was registered at the outpatient clinic. The MRSA strains resembled the sensitive, inbred 'Norwegian type' described four years earlier at UUH, showing a relatively low and heterogenic methicillin resistance (MIC 12-96 mg/L), and susceptibility to most other anti-staphylococcal agents. Before and during the outbreak, there was high activity, understaffing, overcrowding and a mix of patients; 42% of the staff were relatively untrained, and up to 62% (during weekends) were extra nursing staff, partly from other Scandinavian countries. All cases were isolated (air and contact isolation), and all other patients and personnel were treated as being exposed to MRSA (isolated from other departments) until the last patient had been identified, disinfection of all rooms was complete, and all screening samples from staff and other patients were negative. The NICU and the delivery suite were closed for one week for disinfection and screening. The outbreak ended after 34 days. Since then, two years later, no further cases have been detected in the NICU or the delivery suite.

MRSA patients: proven methods to treat colonization and infection

Methicillin-resistant Staphylococcus aureus (MRSA) infections continue to cause serious nosocomial infections in many hospitals. Measures used to control the spread of these infections include ongoing laboratory-based surveillance, placing colonized and infected patients in isolation, use of barrier precautions and handwashing and hand antisepsis. Culturing hospitalized patients at high risk of acquiring MRSA can facilitate detection and isolation of colonized patients. Eradicating MRSA nasal colonization among affected patients and healthcare personnel has also been as a control measure, with variable success. Eradicating MRSA nasal carriage from epidemiologically-implicated healthcare workers has been used on a number of occasions to control outbreaks. Attempts to eradicate MRSA colonization among affected patients has proven difficult. Of more than 40 different decolonization regimens that have been tested during the last 60 years, topical intranasal application of mupirocin ointment has proven to be the most effective. However, intranasal application of mupirocin has limited effectiveness in eradicating colonization in patients who carry the organism at multiple body sites. Furthermore, because decolonization of patients has virtually always been used in combination with other control measures, its efficacy has been difficult to determine. Because MRSA is transmitted primarily on the hands of healthcare workers, greater emphasis should be given to improving hand hygiene practices among health personnel. For patients infected with MRSA, vancomycin remains a drug of choice.

Case 40: ward management. Ward sister who failed to manage her ward appropriately

This article reviews the factors that impinge on the application of topical medications in wound care. The role of systemic and topical antibiotics in wound care is reviewed. Similarly, two antiseptics — iodine and silver, of great current interest in wound management — are scrutinized. The value of these topical agents in the management of wound bioburden should be ascertained from the perspective of understanding the advantages and disadvantages of their use and not established from what is currently the trend.

Genetic homogeneity among methicillin-resistant Staphylococcus aureus strains from Saudi Arabia

Ninety-four strains of methicillin-resistant Staphylococcus aureus (MRSA) were collected from patients nursed in several hospitals in Saudi Arabia, before they were referred to King Faisal Specialist Hospital and Research Centre for tertiary care. The hospitals were from geographically diverse regions and as such the entirety of Saudi Arabia was covered. All strains were genetically typed by random amplification of polymorphic DNA (RAPD) analysis using three different primers and a representative subset of the strains was analyzed with pulsed-field gel electrophoresis (PFGE) as well. It was concluded that 87 out of 94 (93%) belong to a single clonally related lineage of MRSA. In the other 7 cases, the DNA banding patterns were shown to differ only slightly from those determined for the clonal type. PFGE analysis confirmed the homogeneity of the collection of strains. When the RAPD and PFGE fingerprints obtained for the Saudi clone were compared to those generated for a collection of MRSA with a more diverse geographical background, it was shown that the clonal type from Saudi Arabia was not identical to any of these MRSA strains. Our data provide another example of the capacity of certain MRSA clones to expand through entire nations and establish themselves permanently among large number of hospitals and, consequently, even larger numbers of patients.

Preliminary analysis of the transmission dynamics of nosocomial infections: stochastic and management effects

A simple mathematical model is developed for the spread of hand-borne nosocomial pathogens such as Staphylococcus aureus within a general medical-surgical ward. In contrast to previous models a stochastic approach is used. Computer simulations are used to explore the properties of the model, and the results are presented in terms of the pathogen's successful introduction rate, ward-level prevalence, and colonized patient-days, emphasizing the general effects of changes in management of patients and carers. Small changes in the transmissibility of the organism resulted in large changes in all three measures. Even small increases in the frequency of effective handwashes were enough to bring endemic organisms under control. Reducing the number of colonized patients admitted to the ward was also an effective control measure across a wide range of different situations. Increasing surveillance activities had little effect on the successful introduction rate but gave an almost linear reduction in colonized patient-days and ward-level prevalence. Shorter lengths of patient stay were accompanied by higher successful introduction rates, but had little effect on the other measures unless the mean time before detection of a colonized individual was large compared to the mean length of stay. We conclude that chance effects are likely to be amongst the most important factors in determining the course of an outbreak. Mathematical models can provide valuable insights into the non-linear interactions between a small number of processes, but for the very small populations found in hospital wards, a stochastic approach is essential.

Control of methicillin-resistant Staphylococcus aureus in the hospital setting

Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of nosocomial infections. Healthcare professionals in the United States should develop programs to prevent transmission of this organism within their institutions. Aggressive control efforts are justified for several reasons: (1) the incidence of nosocomial MRSA reflects the general effectiveness of infection control practice; (2) MRSA do not replace susceptible strains but instead increase the overall rate of nosocomial S. aureus infections; (3) MRSA infections cause substantial morbidity and mortality; (4) serious MRSA infections must be treated with vancomycin. Thus, in hospitals with high rates of MRSA, use of this antimicrobial agent increases, which in turn may increase the risk for selecting vancomycin-resistant enterococci. Hospitals have used numerous different approaches to control nosocomial spread of MRSA. Staff should choose a control method based on the prevalence of MRSA in their institution and in their referring facilities, the rate of nosocomial transmission of MRSA in their hospital, the risk factors present in their patient population, the reservoirs and modes of transmission specific to their hospital, and their resources. Any MRSA control plan must stress adherence to basic infection control measures, such as hand washing and contact isolation precautions. In addition, decolonization of patients and staff, control of antimicrobial use, surveillance cultures, and molecular typing may be helpful adjuncts.

A Norwegian nosocomial outbreak of methicillin-resistant Staphylococcus aureus resistant to fusidic acid and susceptible to other antistaphylococcal agents

In Norway, infections caused by methicillin resistant Staphylococcus aureus (MRSA) are still uncommon. From December 1993 to January 1997, MRSA was isolated from 22 people in Oslo county; 17 patients and five carriers (healthcare workers). A cluster of ten people (five patients and five healthcare workers) were associated with an outbreak at two hospitals in Oslo. The five patients were all admitted to the same intensive care unit (ICU) at Ullevål University Hospital between May-July 1995 (they were not transferred from abroad) and treated for acute neurological lesions. After surgery, four of them (one died) were transferred to another hospital for rehabilitation and training. The presence of MRSA was discovered in the patients and the five healthcare workers during the 10 months June 1995-March 1996. All cluster strains showed an unusual antibiotic resistance pattern in vitro, with a relatively low degree of methicillin resistance, resistance to fusidic acid, but sensitivity to all other anti-staphylococcal agents. A clonal spread of this fusidic acid resistant MRSA was supported by strain typing using pulsed-field gel electrophoresis (PFGE), which showed that all ten cluster strains belonged to one type or its subtype.

The economic impact of Staphylococcus aureus infection in New York City hospitals

We modeled estimates of the incidence, deaths, and direct medical costs of Staphylococcus aureus infections in hospitalized patients in the New York City metropolitan area in 1995 by using hospital discharge data collected by the New York State Department of Health and standard sources for the costs of health care. We also examined the relative impact of methicillin-resistant versus -sensitive strains of S. aureus and of community-acquired versus nosocomial infections. S. aureus-associated hospitalizations resulted in approximately twice the length of stay, deaths, and medical costs of typical hospitalizations; methicillin-resistant and -sensitive infections had similar direct medical costs, but resistant infections caused more deaths (21% versus 8%). Community-acquired and nosocomial infections had similar death rates, but community-acquired infections appeared to have increased direct medical costs per patient ($35,300 versus $28,800). The results of our study indicate that reducing the incidence of methicillin-resistant and -sensitive nosocomial infections would reduce the societal costs of S. aureus infection.

A rapid (20 h) solid screening medium for detecting methicillin-resistant Staphylococcus aureus

Methicillin aztreonam mannitol salt agar is a sensitive and reliable solid screening medium for detecting methicillin-resistant Staphylococcus aureus (MRSA). With this medium an incubation period of only 20 h is sufficient to either produce visible colonies of MRSA or to exclude MRSA (no staphylococcal colonies). Coagulase testing (requiring a further 6 h) enables coagulase-positive isolates to be provisionally reported as 'possible MRSA' 26-30 h after the swabs were collected. The medium supports growth of intrinsically resistant staphylococci including low-expression-class MRSA (methicillin minimum inhibitory concentration (MIC) 8-16 mg/L), but methicillin susceptible staphylococci and beta-lactamase hyperproducers are suppressed.

Rapid and specific molecular identification of methicillin-resistant Staphylococcus aureus in endotracheal aspirates from mechanically ventilated patients

Multiplex amplification of femA and mecA genetic determinants allowed an early and rapid identification of methicillin-resistant Staphylococcus aureus (MRSA) in endotracheal aspirates of mechanically ventilated patients. femA and/or mecA amplification and bacteriological results were concordant in 57 of 60 samples. In all three discrepant cases, complementary bacteriological tests confirmed the presence of MRSA first identified by molecular analysis. These results underline the value and rapidity of this molecular diagnosis for MRSA infection and control surveillance in intensive care units. Rapid MRSA detection is expected to have a significant clinical impact not only on patient outcome but also on the costs for isolation and treatment.

Methicillin-resistant Staphylococcus aureus in burns patients--why all the fuss?

Procedures designed to limit spread of methicillin-resistant Staphylococcus aureus (MRSA) in burns units demand time and resources. To assess the significance of MRSA in burns patients we performed a retrospective review of MRSA colonization in in-patients over a 41-month period at the North Trent Sub-regional Burns Unit. Patients were compared with MRSA free controls, matched for age and percentage body surface area (BSA) burn and admitted during the same time period. Length of stay, number of operations and deaths were outcome indicators. All patients managed non-operatively were excluded, leaving 40 MRSA patients and 46 controls. There was no statistical difference between the two groups with regard to number of operations (p= 0.07), duration of admission (p = 0.12) or mortality (p = 0.09). Of the control group, 83% had wound swabs positive for methicillin-sensitive Staphylococcus aureus (MSSA). there was no statistical difference in any outcome variables between this sub-group of controls and MRSA patients. Colonization with S. aureus (both MRSA and MSSA) was associated with larger burns (p<0.05), twice as many operative procedures (p<0.05) and prolonged admissions (p<0.01). Mortality was unaltered by staphylococcal colonization (p = 0.8). Although our study lacks power, we would suggest that methicillin resistance per se is not associated with increased morbidity or mortality in burns patients.

Polymerase chain reaction-mediated typing of microorganisms: tracking dissemination of genes and genomes

The polymerase chain reaction (PCR) is a powerful molecular biology tool which can be used for the identification of species and strains of diverse microorganisms. By aimed amplification of characteristic genes (i.e., genes encoding ribosomal RNA molecules) and subsequent genetic analysis of amplified fragments, information on microbiological systematics and phylogeny can be obtained in a fast and efficient manner. Similar types of gene identification can be used to verify or detect genes responsible for phenotypic characteristics, whereas modified forms of the PCR enable whole genome searches for genetic polymorphisms among strains of a given species. In medical sciences, both strategies, gene and genome variability analysis by PCR, have an increasing impact on the study of the spread of especially those microbes that are multiply resistant to clinically used antibiotics. In this communication we will exemplify the usefulness of PCR-mediated typing of microorganisms from a clinical perspective while focusing on gene- versus genome-scanning. Special emphasis will be placed on analysis of the dissemination and characteristics of methicillin-resistant Staphylococcus aureus (MRSA) strains and bacterial factors providing resistance to penicillin and other beta-lactam antibiotics. Technical limitations and possibilities for improvement will be discussed.

How do I diagnose and treat wound infection?

This article is the first in a ‘How do I?’ series, which will examine various aspects of wound management. With best practice continuously the goal, these articles will explore options and provide the nurse with practical advice on how to tackle the issues in question. The first article in the series aims to answer the question: ‘How do I diagnose and treat wound infection?’

Methicillin-resistant Staphylococcus aureus versus the burn patient

Methicillin-resistant Staphylococcus aureus (MRSA) has become a frequent cause of nosocomial infection, its increasing prevalence posing serious therapeutic and infection control problems within the hospital environment. MRSA is a major challenge to the burn patient, with potential to cause significant morbidity and mortality. Burn patients have been shown to become colonised and infected more readily than other patient groups. Extensive burn injuries are particularly susceptible to infection as a result of the disruption of the normal skin barrier and accompanying depression of immune responses. Extended hospitalisation and antibiotic therapy have been identified as additional risk factors for MRSA carriage and infection. Microbial surveillance, epidemiological studies and the introduction of strict infection control regimes can reduce the prevalence of MRSA but may be insufficient for eradication or prevention of outbreak situations. Recognition of the clinical importance of MRSA to the burn patient highlights the need to take appropriate measures to minimise transmission and infection in this vulnerable group of patients.

Methicillin-Resistant Staphylococcus Aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a cause of increasing concern to health-care professionals, as it affects large numbers of patients, with varying degrees of severity.

Vancomycin resistance in staphylococci

Recent emergence of vancomycin resistance in methicillin-resistant Staphylococcus aureus (VRSA) has posed a new threat to hospital infection control and antibiotic chemotherapy. Relatively low-level resistance of VRSA compared to that of vancomycin-resistant enterococci (VRE), and prevalence of S. aureus clinical strains heterogeneously resistant to vancomycin (hetero-VRSA), challenge the value of routine antibiotic susceptibility tests as a tool for the prediction of clinical efficacy of vancomycin therapy. This review summarizes the history of emergence of glycopeptide resistance in staphylococci and considers the mechanism of resistance in these organisms.

Resistance to methicillin and other antibiotics in isolates of Staphylococcus aureus from blood and cerebrospinal fluid, England and Wales, 1989-95

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) strains are colonising hospital patients in most areas of England and Wales, UK. The extent to which they cause invasive infection can be gauged from their presence in isolates from blood or cerebrospinal fluid.

METHODS

About 200 clinical laboratories reported the results of susceptibility testing of between 4501 and 6370 isolates of S aureus from blood or cerebrospinal fluid in each of the years 1989-95. We assessed the rate of resistance to methicillin and other antibiotics for each of these years.

FINDINGS

Resistance to methicillin was stable at about 1.5% of isolates during 1989-91, but increased thereafter to 13.2% in 1995 (p < 0.001). At the same time there was a significant increase in the percentage of isolates resistant to erythromycin, clindamycin, ciprofloxacin, gentamicin, trimethoprim, and rifampicin (p < 0.001 for each)-resistance characteristics often seen in MRSA. Resistance to benzylpenicillin increased slightly but significantly (p < 0.001); resistance to fusidic acid was stable (p > 0.05); resistance to tetracycline decreased significantly (p < 0.001).

INTERPRETATION

Among cases of S aureus bacteraemia, the proportion due to MRSA has increased significantly. Bacteraemia due to MRSA has a poor prognosis, especially if not treated with suitable antibiotics. Therefore, these findings are important, especially for management of patients and the development of antibiotic policies.

Distribution of bacteria on hands and the effectiveness of brief and thorough decontamination procedures using non-medicated soap

Our perception of the role of hand washing in the clinical situation is based on experimental studies in which test-bacteria are usually inoculated onto the skin surface and removed using hand washing preparations containing antiseptics. In this study, we have investigated the distribution of bacteria on the hands of volunteers and the effectiveness of long (3 minute) and brief (10 second) washes in removing both naturally-occurring and artificially-inoculated bacteria (Micrococcus sp.), using only soap and water. There was a tenfold reduction in median counts of artificially inoculated bacteria following both long and brief washes. However, less than 50% of naturally-occurring bacteria were removed and, for hands previously disinfected by immersion in 70% ethanol, the washing procedure increased bacterial counts. In both unwashed hands, and hands washed following a strict protocol, the mean variation in counts of naturally-occurring bacteria at different sites (wrists, dorsal surface, palmar surface, fingertips and interdigital spaces) was only two-fold. The efficiency of recovery of naturally-occurring organisms was estimated by repeated swabbing, to be more than 60%. The data question the value of typical hand wash procedures recommended by many authorities for use in clinical situations and of the perfunctory hand washes frequently adopted by nursing staff in busy wards. Experimental evidence is required to justify procedures and to identify the precise circumstances in which they are of value.

Methicillin-resistant Staphylococcus aureus

This article examines some of the issues involved in the management and control of MRSA colonisation and infection in wounds.

Rapid diagnosis of methicillin-resistant Staphylococcus aureus bacteremia by nested polymerase chain reaction

OBJECTIVE

The purpose of this study was to establish a rapid and sensitive diagnostic method for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia in postoperative patients.

SUMMARY BACKGROUND DATA

As a result of diffusion and abuse of third-generation cephalosporin antibiotics in the 1980s in Japan, an outbreak of MRSA infection has been posed. In the field of surgery, severe postoperative infections with MRSA such as MRSA bacteremia, which may lead to multiple organ failure, have emerged with a high mortality.

METHODS

Thirty-five patients with high fever (above 38.5 C) or watery diarrhea or both within 2 weeks after gastrointestinal major surgery and 6 healthy volunteers were examined. Nested polymerase chain reaction was used to detect mecA and toxic shock syndrome toxin-1 (TSST-1) genes in blood specimens.

RESULTS

The mecA and TSST-1 genes were not detected in the blood samples of any of the six healthy volunteers. In all 12 samples from which MRSA colonies were isolated by blood culture, mecA and TSST-1 genes were detected. Although it took at least 48 hours to identify MRSA by the blood culture method, the presence of mecA and TSST-1 genes was determined by nested polymerase chain reaction method within only 3 to 4 hours after blood sampling.

CONCLUSIONS

This method, as a sensitive and rapid monitoring system for MRS bacteremia, would be clinically beneficial for prevention of cross infection and for early determination of appropriate treatment for infected patients.