Screening for methicillin-resistant Staphylococcus aureus in the endemic hospital: what have we learned?

Development and external validation of a clinical prediction model for MRSA carriage at hospital admission in Southeast Lower Saxony, Germany

In countries with low endemic Methicillin-resistant Staphylococcus aureus (MRSA) prevalence, identification of risk groups at hospital admission is considered more cost-effective than universal MRSA screening. Predictive statistical models support the selection of suitable stratification factors for effective screening programs. Currently, there are no universal guidelines in Germany for MRSA screening. Instead, a list of criteria is available from the Commission for Hospital Hygiene and Infection Prevention (KRINKO) based on which local strategies should be adopted. We developed and externally validated a model for individual prediction of MRSA carriage at hospital admission in the region of Southeast Lower Saxony based on two prospective studies with universal screening in Braunschweig (n = 2065) and Wolfsburg (n = 461). Logistic regression was used for model development. The final model (simplified to an unweighted score) included history of MRSA carriage, care dependency and cancer treatment. In the external validation dataset, the score showed a sensitivity of 78.4% (95% CI: 64.7-88.7%), and a specificity of 70.3% (95% CI: 65.0-75.2%). Of all admitted patients, 25.4% had to be screened if the score was applied. A model based on KRINKO criteria showed similar sensitivity but lower specificity, leading to a considerably higher proportion of patients to be screened (49.5%).

The Correlation between Airborne Methicillin-resistant Staphylococcus aureus with the Presence of MRSA Colonized Patients in a General Intensive Care Unit

Air sampling directly onto a methicillin-resistant Staphylococcus aureus (MRSA) selective agar was performed at six locations three times weekly over a period of 32 weeks in a new, initially MRSA-free Intensive Care Unit to examine if MRSA is present in air sample cultures and, if so, whether it is affected by the number of MRSA colonized patients present. A total of 480 air samples were collected on 80 days. A total of 39/480 (8.1%) samples were found to be MRSA positive of which 24/160 (15%) positive air samples were from the single rooms, where MRSA colonised patients were isolated, and 15/320 (4.7%) were from the open bed areas. A significant correlation was found between the daily number of MRSA colonized or infected patients in the Unit and the daily number of MRSA positive air samples cultures obtained (r2=0.128; P<0.005). The frequency of positive cultures was significantly higher in the single rooms than in the open bed areas (relative risk=3.2; P<0.001). The results from one of the single rooms showed a strong correlation between the presence of MRSA patients and MRSA positive air samples (relative risk=11.4; P<0.005). Our findings demonstrate that the presence of airborne MRSA in our unit is strongly related to the presence and number of MRSA colonized or infected patients in the Unit.

Disparity of the "screen-and-isolate" policy for multidrug-resistant organisms: A national survey in French adult ICUs

BACKGROUND

The prevalence of multidrug-resistant organisms (MDROs) has dramatically increased. The aim of this survey was to describe and analyze the different screening and isolation policies regarding MDROs in French adult intensive care units (ICUs).

MATERIALS AND METHODS

A multicenter online survey was performed among French ICUs, including 63 questions distributed into 4 parts: characteristics of the unit, MDRO screening policy, policy regarding contact precautions, and ecology of the unit.

RESULTS

From April 2015 to June 2016, 73 of 301 ICUs (24%) participated in the survey. MDRO screening was performed on admission in 96% of ICUs, for at least 1 MDRO (78%). MDRO screening was performed weekly during ICU stay in 83% of ICUs. Preemptive isolation was initiated on admission in 82% of ICUs, mostly in a targeted way (71%). Imported and acquired MDRO rates >10% were reported in 44% and 27% of ICUs, respectively. An MDRO outbreak had occurred within the past 3 years in 48% of cases.

CONCLUSION

French ICUs have variable screening and isolation approaches for MDROs, as up to 10 combinations were met. Discrepancies with the 2009 national guidelines were observed. Very few ICUs practice without some form of screening and isolation of patients upon admission.

Shorter Incubation Times for Detecting Multi-drug Resistant Bacteria in Patient Samples: Defining Early Imaging Time Points Using Growth Kinetics and Total Laboratory Automation

Background

The transition from manual processing of patient samples to automated workflows in medical microbiology is challenging. Although automation enables microbiologists to evaluate all samples following the same incubation period, the essential incubation times have yet to be determined. We defined essential incubation times for detecting methicillin-resistant Staphylococcus aureus (MRSA), multi-drug resistant gram-negative bacteria (MDRGN), and vancomycin-resistant enterococci (VRE).

Methods

We monitored the growth kinetics of MRSA, MDRGN, and VRE between two and 48 hours on chromogenic media to establish the time points of first growth, single colony appearance, and typical morphology for 10², 10⁴, 10⁶, and 10⁸ colony forming units/mL. Subsequently, we imaged plates inoculated with 778 patient samples after 20, 24, and 36 hours.

Results

The first growth, single colony appearance, and typical morphology time points were inoculum-dependent. First growth appeared after 6–18 hours, 4–18 hours, and 8–48 hours for MRSA, MDRGN, and VRE, respectively, and single colonies appeared at 12–18 hours, 6–20 hours, and 12–48 hours, respectively. Typical morphology was visible at 14–22 hours and 12–48 hours for MRSA and VRE, but was not determined for MDRGN. By examining patient samples, ≥98% of MRSA and MDRGN were visible 20 hours after the start of incubation. Following 24 hours of incubation, only 79.5% of VRE were clearly visible on the respective plates.

Conclusions

An incubation time of 20 hours is sufficient for detecting MRSA and MDRGN. VRE growth is much slower and requires additional imaging after 36 hours.

Cost Analysis of Universal Screening vs. Risk Factor-Based Screening for Methicillin-Resistant Staphylococcus aureus (MRSA)

Background

The literature remains conflicted regarding the most effective way to screen for MRSA. This study was designed to assess costs associated with universal versus risk factor-based screening for the reduction of nosocomial MRSA transmission.

Methods

The study was conducted at The Ottawa Hospital, a large multi-centre tertiary care facility with approximately 47,000 admissions annually. From January 2006-December 2007, patients underwent risk factor-based screening for MRSA on admission. From January 2008 to August 2009 universal MRSA screening was implemented. A comparison of costs incurred during risk factor-based screening and universal screening was conducted. The model incorporated probabilities relating to the likelihood of being tested and the results of polymerase chain reaction (PCR) testing with associated effects in terms of MRSA bacteremia and true positive and negative test results. Inputted costs included laboratory testing, contact precautions and infection control, private room costs, housekeeping, and length of hospital stay. Deterministic sensitivity analyses were conducted.

Results

The risk factor-based MRSA screening program screened approximately 30% of admitted patients and cost the hospital over $780 000 annually. The universal screening program screened approximately 83% of admitted patients and cost over $1.94 million dollars, representing an excess cost of $1.16 million per year. The estimated additional cost per patient screened was $17.76.

Conclusion

This analysis demonstrated that a universal MRSA screening program was costly from a hospital perspective and was previously known to not be clinically effective at reducing MRSA transmission. These results may be useful to inform future model-based economic analyses of MRSA interventions.

The Decrease in Healthcare-Associated Methicillin-Resistant Staphylococcus aureus Infections and Savings From Glycopeptide Use

We evaluated changes in the rate of healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) infections and healthcare-associated S. aureus infections after implementation of infection control precautions and the effect of this on glycopeptide use and expenditures for glycopeptides in a private medical center in Turkey in the years 2000-2005. A striking decrease was obtained in the number of MRSA infections, and the expenditure for glycopeptide use also decreased

Modeling Transmission of Methicillin-ResistantStaphylococcus AureusAmong Patients Admitted to a Hospital

Objective:

To determine the impact of the screening test, nursing workload, handwashing rates, and dependence of handwashing on risk level of patient visit on methicillin-resistantStaphylococcus aureus(MRSA) transmission among hospitalized patients.

Setting:

General medical ward.

Methods:

Monte Carlo simulation was used to model MRSA transmission (median rate per 1,000 patient-days). Visits by healthcare workers (HCWs) to patients were simulated, and MRSA was assumed to be transmitted among patients via HCWs.

Results:

The transmission rate was reduced from 0.89 to 0.56 by the combination of increasing the sensitivity of the screening test from 80% to 99% and being able to report results in 1 day instead of 4 days. Reducing the patient-to-nurse ratio from 4.3 in the day and 6.8 at night to 3.8 and 5.7, respectively, reduced the number of nosocomial infections from 0.89 to 0.85; reducing the ratio to 1 and 1, respectively, further reduced the number of nosocomial infections to 0.32. Increases in handwashing rates by 0%, 10%, and 20% for high-risk visits yielded reductions in nosocomial infections similar to those yielded by increases in handwashing rates for all visits (0.89, 0.36, and 0.24, respectively). Screening all patients for MRSA at admission reduced the transmission rate to 0.81 per 1,000 patient-days from 1.37 if no patients were screened.

Conclusion:

Within the ranges of parameters studied, the most effective strategies for reducing the rate of MRSA transmission were increasing the handwashing rates for visits involving contact with skin or bodily fluid and screening patients for MRSA at admission. (Infect Control Hosp Epidemiol 2005;26:607- 615)

Methicillin-ResistantStaphylococcus AureusCarriage Among Patients After Hospital Discharge

Background and Objective:

At the University Medical Center Utrecht (UMCU), follow-up implies an inventory of risk factors and screening for MRSA colonization among all MRSA-positive patients for at least 6 months. If risk factors or positive cultures persist or re-emerge, longer follow-up is indicated and isolation at readmission. This study investigated how long MRSA-positive patients remained colonized after hospital discharge and which risk factors were important. Furthermore, the results of eradication therapy were evaluated.

Design:

All patients who were positive for MRSA at the UMCU between January 1991 and January 2001 were analyzed regarding carriage state, presence of risk factors for prolonged carriage ofStaphylococcus aureus, and eradication treatment.

Results:

A total of 135 patients were included in the study. The median follow-up time was 1.2 years. Eighteen percent of the patients were dismissed from follow-up 1 year after discharge. Only 5 patients were dismissed after 6 months. Among patients with no risk factors, eradication treatment was effective for 95% within 1 year. Among patients with persistent risk factors, treatment was effective for 89% within 2 years.

Conclusions:

Based on these findings, eradication therapy should be prescribed for all MRSA carriers, independent of the presence of risk factors. MRSA-positive patients should be evaluated for 6 months for the presence of risk factors and MRSA carriage. Screening for risk factors is important because intermittent MRSA carriage was found in a significant number of our patients. Patients with negative MRSA cultures and without risk factors for 12 months can be safely dismissed from follow-up. (Infect Control Hosp Epidemiol 2005;26:629-633)

Prospective Two-Center Comparison of Three Chromogenic Agars for Methicillin-Resistant Staphylococcus aureus Screening in Hospitalized Patients

Three chromogenic media, chromID MRSA SMART (SMART), chromID MRSA first generation (chromID), and Brilliance MRSA (OX2), were evaluated for methicillin-resistant Staphylococcus aureus (MRSA) screening using 1,220 samples. The sensitivity at 24 h was significantly better with the SMART agar (66.4%) than that with chromID agar (50.5%). Enrichment and incubation until 48 h are still needed for an optimal yield.

Effect of Screening for Methicillin-Resistant Staphylococcus aureus Carriage by Polymerase Chain Reaction on the Duration of Unnecessary Preemptive Contact Isolation

A high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) carriage at hospital readmission among previous MRSA carriers warrants screening and preemptive isolation precautions. The replacement of culture on chromogenic agar with rapid quantitative polymerase chain reaction for readmission screening reduces the number of unnecessary preemptive isolation-days by 54% (from 6.88 to 3.14 isolation-days) and related costs by 45% (from US$113.2 to US$62.1) for patients who test negative for MRSA.

Highly Effective Regimen for Decolonization of Methicillin-ResistantStaphylococcus aureusCarriers

Objective.

To evaluate the efficacy of a standardized regimen for decolonization of methicillin-resistantStaphylococcus aureus(MRSA) carriers and to identify factors influencing decolonization treatment failure.

Design.

Prospective cohort study from January 2002 to April 2007, with a mean follow-up period of 36 months.

Setting.

University hospital with 750 beds and 27,000 admissions/year.

Patients.

Of 94 consecutive hospitalized patients with MRSA colonization or infection, 32 were excluded because of spontaneous loss of MRSA, contraindications, death, or refusal to participate. In 62 patients, decolonization treatment was completed. At least 6 body sites were screened for MRSA (including by use of rectal swabs) before the start of treatment.

Interventions.

Standardized decolonization treatment consisted of mupirocin nasal ointment, chlorhexidine mouth rinse, and full-body wash with chlorhexidine soap for 5 days. Intestinal and urinary-tract colonization were treated with oral vancomycin and cotrimoxazole, respectively. Vaginal colonization was treated with povidone-iodine or, alternatively, with chlorhexidine ovula or octenidine solution. Other antibiotics were added to the regimen if treatment failed. Successful decolonization was considered to have been achieved if results were negative for 3 consecutive sets of cultures of more than 6 screening sites.

Results.

The mean age (± standard deviation [SD]) age of the 62 patients was 66.2 ± 19 years. The most frequent locations of MRSA colonization were the nose (42 patients [68%]), the throat (33 [53%]), perianal area (33 [53%]), rectum (36 [58%]), and inguinal area (30 [49%]). Decolonization was completed in 87% of patients after a mean (±SD) of 2.1 ± 1.8 decolonization cycles (range, 1-10 cycles). Sixty-five percent of patients ultimately required peroral antibiotic treatment (vancomycin, 52%; cotrimoxazole, 27%; rifampin and fusidic acid, 18%). Decolonization was successful in 54 (87%) of the patients in the intent-to-treat analysis and in 51 (98%) of 52 patients in the on-treatment analysis.

Conclusion.

This standardized regimen for MRSA decolonization was highly effective in patients who completed the full decolonization treatment course.

Infection control in the intensive care unit

It is critical for health care personnel to recognize and appreciate the detrimental impact of intensive care unit (ICU)-acquired infections. The economic, clinical, and social expenses to patients and hospitals are overwhelming. To limit the incidence of ICU-acquired infections, aggressive infection control measures must be implemented and enforced. Researchers and national committees have developed and continue to develop evidence-based guidelines to control ICU infections. A multifaceted approach, including infection prevention committees, antimicrobial stewardship programs, daily reassessments-intervention bundles, identifying and minimizing risk factors, and continuing staff education programs, is essential. Infection control in the ICU is an evolving area of critical care research.

A bundled approach to reduce methicillin-resistant Staphylococcus aureus infections in a system of community hospitals

Methicillin-resistant Staphylococcus aureus (MRSA) infections pose a significant challenge to U.S. healthcare facilities, but there has been limited study of initiatives to reduce infection and increase patient safety in community hospitals. To address this need, a multifaceted program for MRSA infection prevention was developed for implementation in 159 acute care facilities. This program featured five distinct tools-active MRSA surveillance of high-risk patients, enhanced barrier precautions, compulsive hand hygiene, disinfection and cleaning, and executive champions and patient empowerment-and was implemented during 1Q-2Q 2007. Postintervention (3Q 2007-2Q 2008), 10.2% of patients with high-risk for infection or complications due to MRSA had nasal colonization. Volume of disposable gown and alcohol-based hand sanitizer use increased substantially following program implementation. Self-reported rates, based on NHSN definitions, of healthcare-associated central line-associated bloodstream infections and ventilator-associated pneumonia due to MRSA decreased 39% (p < .001) and 54% (p < .001), respectively. Infection rates continued to decrease during the follow-up period (1Q-4Q 2009). This sustained improvement demonstrates that reducing healthcare-associated MRSA infections in a large number of diverse facilities is possible and that a "bundled" approach that translates science into clinical and executive performance expectations may aid in overcoming traditional barriers to implementation.

Review of a major epidemic of methicillin-resistant Staphylococcus aureus: the costs of screening and consequences of outbreak management

BACKGROUND

A major outbreak of methicillin-resistant Staphylococcus aureus (MRSA) occurred in locations C and Z of our hospital and lasted for several years. It affected 1,230 patients and 153 personnel.

METHODS

Outbreak management was installed according to the Dutch "search and destroy" policy. A rapid, high-throughput method for molecular screening of potential MRSA carriers was implemented. Outbreak isolates were retrospectively genotyped by pulsed field gel electrophoresis. Costs of molecular screening were compared with screening by culture.

RESULTS

Genotyping results revealed 4 distinct epidemic MRSA clones. Three were present in hospital C. Because of a merger of hospitals, these clones spread to hospital Z. Another clone of MRSA affected other health care-related institutions in the region. Because of the implementation of strict containment measures of the "search and destroy" policy, the annual number of tests decreased from 100,000 to 18,000. The disposables and reagents used in polymerase chain reaction technology are more expensive than those of conventional methods. However, the clinical and economic benefits of fast results in regard to expenses of the hospital clearly outweigh the higher costs of screening.

CONCLUSION

The implementation of a rapid, high-throughput molecular screening system greatly contributed to the effectiveness of strict containment measures of the "search and destroy" policy. The major epidemic clones of MRSA in the outbreak were eradicated by this strategy.

Infection control in United Kingdom neonatal units: variance in practice and the need for an evidence base

Infection prevention is a cornerstone of good neonatal care. There are, however, few research data to support infection control approaches in this population. Through a structured telephone interview we surveyed all neonatal units in the United Kingdom to identify infection control issues, practices and policies. Eighty seven percent of the 198 neonatal units participated. Twenty one units (12.2%) had closed with infection control issues in the last year; 14.1% had current infection control concerns; 81.5% of units decolonised MRSA positive infants, but over 15 regimens were used. Wide variations in hygiene measures were identified; 22.1% of units used theatre scrubs for all staff, 7.6% used aprons and 5.8% required gloves to be worn when entering clinical areas. Only 54% required hand washing and alcohol gel before entry to a patient care area; 11.6% required only the use of alcohol gel.

Although infection control issues are resulting in neonatal unit closures and risks to patients, there are considerable variations in hygiene and screening practices. There is little data to support the safety or efficacy of decolonisation in neonatal populations, but this is widely practised. Research needs to be carried out to evaluate the effectiveness of screening practices and decolonisation in order that a consistent evidence-based approach can be applied.

Single-nucleotide polymorphism genotyping identifies a locally endemic clone of methicillin-resistant Staphylococcus aureus

We developed, tested, and applied a TaqMan real-time PCR assay for interrogation of three single-nucleotide polymorphisms that differentiate a clade (termed 't003-X') within the radiation of methicillin-resistant Staphylococcus aureus (MRSA) ST225. The TaqMan assay achieved 98% typeability and results were fully concordant with DNA sequencing. By applying this assay to 305 ST225 isolates from an international collection, we demonstrate that clade t003-X is endemic in a single acute-care hospital in Germany at least since 2006, where it has caused a substantial proportion of infections. The strain was also detected in another hospital located 16 kilometers away. Strikingly, however, clade t003-X was not found in 62 other hospitals throughout Germany nor among isolates from other countries, and, hence, displayed a very restricted geographical distribution. Consequently, our results show that SNP-typing may be useful to identify and track MRSA clones that are specific to individual healthcare institutions. In contrast, the spatial dissemination pattern observed here had not been resolved by other typing procedures, including multilocus sequence typing (MLST), spa typing, DNA macrorestriction, and multilocus variable-number tandem repeat analysis (MLVA).

Risk factors for positive admission surveillance cultures for methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci in a neurocritical care unit

OBJECTIVE

Hospitals are under increasing pressure to perform active surveillance cultures for methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus. This study aimed to identify patients at low and high risk for positive admission surveillance cultures for methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus in a neurocritical care unit using readily ascertainable historical factors.

DESIGN

Before/after study with nested case/control study.

SETTING

Neurocritical care unit of an academic hospital.

PATIENTS

During the intervention period (July 2007 to June 2008), after implementation of an admission surveillance culture screening program for methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus, 2,059 patients were admitted to the neurocritical care unit for a total of 5,957 patient days.

INTERVENTIONS

Cases had positive methicillin-resistant Staphylococcus aureus or vancomycin-resistant Enterococcus admission surveillance cultures within 48 hrs of hospital admission. Controls had negative cultures.

MEASUREMENTS AND MAIN RESULTS

Admission surveillance cultures grew methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus in 35 of 823 (4.3%) and 19 of 766 (2.5%) patients, respectively. Factors significantly associated with both methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus colonization were intravenous antibiotics and hospitalization in the past year, immunocompromised health status, intravenous drug use, long-term hemodialysis, and known prior carrier status. Transfer from an outside hospital and residence in a long-term care facility in the past year were associated with vancomycin-resistant Enterococcus colonization. Classification and regression tree analysis was used to identify variables that best predicted positive methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus surveillance cultures. A classification and regression tree model with six of these variables yielded an overall cross-validated predictive accuracy of 87.12% to detect methicillin-resistant Staphylococcus aureus colonization. For vancomycin-resistant Enterococcus, a four-variable classification and regression tree model (intravenous antibiotics, hospitalization and long-term patient care in the past year, and not being "admitted same day of procedure") optimized the predictive accuracy (94.91%). There were no cases of vancomycin-resistant Enterococcus colonization in patients admitted same day of procedure.

CONCLUSIONS

Colonization with methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus in neurocritical care patients can be predicted with a high predictive accuracy using decision trees that include four to six readily attainable risk factors. In our setting, in the absence of these risk factors and in patients admitted from home for neurosurgical procedures, routine admission surveillance cultures to the intensive care unit may not be cost-effective.

The management of infection and colonization due to methicillin-resistant Staphylococcus aureus: A CIDS/CAMM position paper

Methicillin-resistant Staphylococcus aureus (MRSA) is being seen with greater frequency in most hospitals and other health care facilities across Canada. The organism may cause life-threatening infections and has been associated with institutional outbreaks. Several studies have confirmed that MRSA infection is associated with increased morbidity and mortality compared with infections caused by susceptible strains, even when the presence of comorbidities is accounted for. Treatment of MRSA infection is complicated by the fact that these organisms are resistant to multiple antimicrobial agents, so treatment options are limited. The effectiveness of decolonization therapy (attempting to eradicate MRSA carriage) is also uncertain. This paper reviews the medical management of MRSA infections, discusses the potential role of decolonization and provides an overview of evidence to support recommended infection control practices.

Epidemiology and virulence insights from MRSA and MSSA genome analysis

Staphylococcus aureus is a major human pathogen responsible for a wide diversity of infections ranging from localized to life threatening diseases. From 1961 and the emergence of methicillin-resistant S. aureus (MRSA), this bacterium has shown a particular capacity to survive and adapt to drastic environmental changes and since the beginning of the 1990s it has spread worldwide. Until recently, S. aureus was considered as the prototype of a nosocomial pathogen but it has now been recognized as an agent responsible for outbreaks in the community. Several recent reports suggest that the epidemiology of MRSA is changing. Understanding of pathogenicity, virulence and emergence of epidemic clones within MRSA populations is not clearly defined, despite several attempts to identify common molecular features between strains that share similar epidemiological and/or virulence behavior. These studies included: pattern profiling of bacterial adhesins, analysis of clonal complex groups, molecular genotyping and enterotoxin content analysis. To date, all approaches failed to find a correlation between molecular determinants and clinical outcomes. We hypothesize that the capacity of the bacterium to become more invasive or virulent is determined by genetics. The utilization of massively parallel methods of analysis is therefore ideal to study the contribution of genetics. Therefore, this article focuses on the entire genome including coding sequences as well as noncoding sequences. This high resolution approach allows the monitoring micro- and macroevolution of MRSA and identification of specific genomic markers of evolution of invasive or highly virulent phenotypes.

[Antibiotic multiresistance in critical care units]

The presence of microorganisms with acquired resistance to multiple antibiotics complicates the management and outcome of critically ill patients. The intensivist, in his/her daily activity, is responsible for the prevention and control of the multiresistance and the challenge of prescribing the appropriate treatment in case of an infection by these microorganisms. We have reviewed the literature regarding the definition, important concepts related to transmission, recommendations on general measures of control in the units and treatment options. We also present data on the situation in our country known primarily through the ENVIN-UCI register. Addressing the multiresistance not only requires training but also teamwork with other specialists and adaptation to the local environment.

High proportion of wrongly identified methicillin-resistant Staphylococcus aureus carriers by use of a rapid commercial PCR assay due to presence of staphylococcal cassette chromosome element lacking the mecA gene

During a 9-month period, 217 patients were newly diagnosed as methicillin-resistant Staphylococcus aureus (MRSA) carriers by using a commercial rapid PCR-based test (GeneXpert). However, no MRSA was recovered by culturing the second swab in 61 of these patients. Further analyses showed that 28 (12.9%) of the patients harbored S. aureus isolates with a staphylococcal cassette chromosome element lacking the mecA gene and were thus incorrectly determined to be MRSA carriers.

Detection of meticillin-resistant staphylococcus aureus (MRSA) colonization in newborn infants using real-time polymerase chain reaction (PCR)

OBJECTIVE

Meticillin-resistant staphylococcus aureus (MRSA) colonization on neonatal units is a common and important clinical problem. Effectiveness of polymerase chain reaction (PCR) for detecting MRSA nasal colonization of infants was evaluated and compared to culture-based methods. The effect of skin decolonization in affected infants was studied.

METHODS

Paired nasal swabs were collected from infants in our neonatal unit over a 12-month period (September 2007-2008). Colonization with MRSA was determined with a commercially available PCR method and compared to culture.

RESULTS

A total of 696 paired nasal swabs were taken. Three infants were colonized at the beginning and were included. There were positive PCRs in 12 infants. Five infants cultured MRSA from a nasal swab at the same time. No infants were culture-positive when PCR was negative (sensitivity 100%, specificity 99% compared to culture). PCR results were available within 24 h. Five infants were PCR+ and isolated meticillin-sensitive Staphylococcus aureus. This organism gave a false-positive PCR result. Two infants transferred in on broad-spectrum antibiotics were PCR+ and negative by culture. Decolonization led to negative nasal PCR and culture in 4/5 infants to discharge.

CONCLUSIONS

PCR methods are sensitive and specific for detection of MRSA colonization in newborn infants of all gestations with results 1-2 days before culture.

Performance of a new chromogenic medium, BBL CHROMagar MRSA II (BD), for detection of methicillin-resistant Staphylococcus aureus in screening samples

Two chromogenic media for the detection of MRSA were compared: BBL CHROMagar MRSA II (BD) and MRSA ID agar (bioMérieux). Following overnight nonselective enrichment, 1,919 screening samples were inoculated on both chromogenic agars. After 24 h, the sensitivities of both media were high and comparable. Both media showed an important decrease in specificity after 48 h of incubation (decreases of 8% for MRSA II and 10% for MRSA ID), but MRSA II was significantly more specific at both time points.

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.

Comparative evaluation of five culture media with triplex PCR assay for detection of methicillin-resistant Staphylococcus aureus

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) is responsible for nosocomial and community-acquired infections. Hence, rapid and accurate laboratory diagnosis of MRSA is a vital constituent of control measures. The present study evaluated five different methods for the identification of MRSA. A total of 207 S. aureus clinical isolates that consisted of 89 MRSA and 118 methicillin-susceptible S. aureus (MSSA) strains confirmed by PCR were tested. MRSA strains were evaluated by five different methods: chromogenic MRSA agar (CMRSA), oxacillin resistance screening agar base (ORSAB), mannitol salt oxacillin agar (MSO), mannitol salt cefoxitin agar with two different concentrations of cefoxitin [4 microg/ml (MSC-4) and 6 microg/ml (MSC-6)]. The results of the different methods were compared to mecA PCR as the gold standard. MSC-6 showed only six false-positive MRSA in comparison with PCR. The sensitivities and specificities of MSC-6, MSC-4, MSO-4, ORSAB, and CMRSA were as follows: 98.9/94.9%, 100/83.1%, 89.9/87.3%, 97.8/96.6%, and 95.5/94.9%, respectively. In comparison with PCR, it was found that both MSC-6 and ORSAB were relatively the least expensive screening tests ($0.70 and $1.00, respectively). In conclusion, all methods were comparable, but MSC-6 was the least expensive medium for MRSA screening.

Polymerase chain reaction screening for methicillin-resistant Staphylococcus aureus and contact isolation

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) infections are thought to now be endemic in some populations. The early identification of individuals admitted to the hospital who are harboring this organism is important for the timely implementation of appropriate control strategies. Our objective was to measure the prevalence of MRSA carriage in high-risk patients entering our hospital and to determine which of these patients screened for MRSA should be placed in contact precautions on admission.

METHODS

Between January 1, 2007, and December 31, 2007, we used polymerase chain reaction analysis, with a turnaround time of 4 hours or less, to screen for MRSA in a select group of patients entering our hospital.

RESULTS

We screened 1,568 patients and found 144 (9.2%) positive. Of the 1,568 patients, 170 (10.8%) were known to previously have been MRSA positive. Of these, 90 (52.9%) had negative screens.

CONCLUSION

We used a rapid screening test to identify patients harboring MRSA. Our findings support that MRSA is harbored sporadically and patients do not have to be placed in contact isolation based on a history of previously being MRSA positive.

Serious infections due to methicillin-resistant Staphylococcus aureus: an evolving challenge for physicians

Methicillin-resistant Staphylococcus aureus (MRSA) is a well-recognized major cause of nosocomial infection worldwide. During the past decade, however, the epidemiology of staphylococcal infections has partially changed, with an increase in the number of patients who acquire infections in the community. The changing epidemiology is a cause for concern among physicians, leading to an increase in the number of patients with infections due to MRSA diagnosed at hospital admission and in the emergency department. The aims of this article are to review the current state of knowledge regarding MRSA infections, to identify those factors which may help physicians to recognize the patients at high risk, and to manage these infections appropriately.

One-year experience with modified BD GeneOhm MRSA assay for detection of methicillin-resistant Staphylococcus aureus from pooled nasal, skin, and throat samples

We report our 1-year experience with modified GeneOhm MRSA assay (formerly IDI-MRSA) for pooled surveillance specimens in low methicillin-resistant Staphylococcus aureus (MRSA) prevalence clinical setting. We have successfully modified the GeneOhm MRSA assay protocol during the specimen preparation step by adding an extra washing step followed by pooling of up to 3 samples per patient (nose, skin, with or without throat) at the lysis step. The sensitivity of the modified assay compared with conventional cultivation was 94.3%, specificity 99.2%, negative predictive value 99.2%, and positive predictive value 94.3%. The modified test is reliable and performed well compared with conventional culture methods in our clinical setting with low-level prevalence of MRSA colonization. Our findings support the use of pooling of the patients samples as a cost-effective way of screening for MRSA colonization.

Evaluation of three chromogenic media (MRSA-ID, MRSA-Select and CHROMagar MRSA) and ORSAB for surveillance cultures of methicillin-resistant Staphylococcus aureus

Screening specimens were homogenised in saline 0.9% w/v before either direct inoculation or following enrichment in broth on three chromogenic media (MRSA-ID, CHROMagar MRSA and MRSA Select) and ORSAB medium for the detection of methicillin-resistant Staphylococcus aureus (MRSA). In total, 102 of 466 specimens yielded MRSA on at least one medium. After incubation for 16-18 h, the sensitivity was 51%, 59%, 47% and 65% on MRSA-ID, CHROMagar MRSA, ORSAB and MRSA Select, respectively, compared with 82%, 75%, 67% and 80%, respectively, after 42 h, and 93%, 95%, 79% and not tested, respectively, following broth enrichment. There were significantly more MRSA colonies on MRSA-Select after 16-18 h than on ORSAB or MRSA ID (p 0.001 and 0.0022, respectively), whereas there were more MRSA colonies after 42 h on MRSA-ID and MRSA-Select than on ORSAB (p 0.0004 and 0.012, respectively). The specificity of the media for identifying MRSA based on the colour of colonies after incubation for 16-18 h was 100%, 99%, 99% and 100%, respectively, compared with 98%, 97%, 98% and 98%, respectively, after 42 h, and 100%, 99%, 100% and not tested, respectively, following broth enrichment. The speed of detection (mean time to report a positive result) was 1.65, 1.72, 2.31 and 1.35 days, respectively. For each of the three media tested following enrichment, the use of an enrichment broth increased the detection rate of MRSA by 16-24%.

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.

Modelling the impact of antibiotic use and infection control practices on the incidence of hospital-acquired methicillin-resistant Staphylococcus aureus: a time-series analysis

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen worldwide. A wide range of factors have been suggested to influence the spread of MRSA. The objective of this study was to evaluate the effect of antimicrobial drug use and infection control practices on nosocomial MRSA incidence in a 426-bed general teaching hospital in Northern Ireland.

METHODS

The present research involved the retrospective collection of monthly data on the usage of antibiotics and on infection control practices within the hospital over a 5 year period (January 2000-December 2004). A multivariate ARIMA (time-series analysis) model was built to relate MRSA incidence with antibiotic use and infection control practices.

RESULTS

Analysis of the 5 year data set showed that temporal variations in MRSA incidence followed temporal variations in the use of fluoroquinolones, third-generation cephalosporins, macrolides and amoxicillin/clavulanic acid (coefficients = 0.005, 0.03, 0.002 and 0.003, respectively, with various time lags). Temporal relationships were also observed between MRSA incidence and infection control practices, i.e. the number of patients actively screened for MRSA (coefficient = -0.007), the use of alcohol-impregnated wipes (coefficient = -0.0003) and the bulk orders of alcohol-based handrub (coefficients = -0.04 and -0.08), with increased infection control activity being associated with decreased MRSA incidence, and between MRSA incidence and the number of new patients admitted with MRSA (coefficient = 0.22). The model explained 78.4% of the variance in the monthly incidence of MRSA.

CONCLUSIONS

The results of this study confirm the value of infection control policies as well as suggest the usefulness of restricting the use of certain antimicrobial classes to control MRSA.

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].

Fatal necrotizing pneumonia due to a Panton-Valentine leukocidin positive community-associated methicillin-sensitive Staphylococcus aureus and Influenza co-infection: a case report

Recent studies have described a number of fatalities due to methicillin-resistant Staphylococcus aureus (MRSA) and influenza virus co-infection. MRSA isolates provide a challenge to caregivers due to inherent wide range antibiotic resistance. Many facilities have instituted screening methods, based on the presence of antibiotic resistance genes, to identify MRSA positive patients upon admission. However, the resistance profile of the pathogen does not necessarily determine the severity of disease caused by that organism.

We describe a fatal case of necrotizing pneumonia in a patient co-infected with Influenza B and a community-associated, PVL-positive methicillin-susceptible Staphylococcus aureus (MSSA).

Methicillin-resistant Staphylococcus aureus (MRSA) detection: comparison of two molecular methods (IDI-MRSA PCR assay and GenoType MRSA Direct PCR assay) with three selective MRSA agars (MRSA ID, MRSASelect, and CHROMagar MRSA) for use with infection-control swabs

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasing problem. Rapid detection of MRSA-colonized patients has the potential to limit spread of the organism. We evaluated the sensitivities and specificities of MRSA detection by two molecular methods (IDI-MRSA PCR assay and GenoType MRSA Direct PCR assay) and three selective MRSA agars (MRSA ID, MRSASelect, and CHROMagar MRSA), using 205 (101 nasal, 52 groin, and 52 axillary samples) samples from consecutive known MRSA-infected and/or -colonized patients. All detection methods had higher MRSA detection rates for nasal swabs than for axillary and groin swabs. Detection of MRSA by IDI-MRSA was the most sensitive method, independent of the site (94% for nasal samples, 80% for nonnasal samples, and 90% overall). The sensitivities of the GenoType MRSA Direct assay and the MRSA ID, MRSASelect, and CHROMagar MRSA agars with nasal swabs were 70%, 72%, 68%, and 75%, respectively. All detection methods had high specificities (95 to 99%), independent of the swab site. Extended incubation for a further 24 h with selective MRSA agars increased the detection of MRSA, with a corresponding decline in specificity secondary to a significant increase in false-positive results. There was a noticeable difference in test performance of the GenoType MRSA Direct assay in detection of MRSA (28/38 samples [74%]) compared with detection of nonmultiresistant MRSA (17/31 samples [55%]) (susceptible to two or more non-beta-lactam antibiotics). This was not observed with selective MRSA agar plates or IDI-MRSA. Although it is more expensive, in addition to rapid turnaround times of 2 to 4 h, IDI-MRSA offers greater detection of MRSA colonization, independent of the swab site, than do conventional selective agars and GenoType MRSA Direct.

Prevalence and risk factors for meticillin-resistant Staphylococcus aureus in adult emergency admissions--a case for screening all patients?

In this study we describe the prevalence and frequency of risk factors for meticillin-resistant Staphylococcus aureus (MRSA) colonization in emergency admissions during a one-year MRSA screening programme. Overall, 7801/13 826 (56.4%) adult emergency admissions by 6469 patients were screened for MRSA. Of those screened, 670/7801 (8.6%) admissions by 433 patients (6.7%) were colonized with MRSA. Risk factors studied were previous hospital admission, previous MRSA colonization and residence in care homes. Patients with any risk factor (MRSA positive: 366/3952 (9.3%) vs MRSA negative: 67/2450 (2.7%), P<0.001), advanced age (mean ages for MRSA positive and negative patients were 74.4 and 56.2 years, respectively (P<0.001)), and increasing frequency of hospital admissions (P<0.001), patients from care homes (41/184, 22.2%) and previous MRSA colonization (232/1855, 12.5%) had a significantly higher MRSA colonization rate. The cost of the screening programme was nearly 24,500 pounds. It was noticed that there was a substantial reduction in hospital-acquired MRSA and MRSA bacteraemia during the study period. The study was not designed to establish whether this reduction was causally associated with the screening programme. We conclude that there is a high MRSA colonization rate among emergency admissions, especially those with risk factors. Using a selective risk factor based screening strategy more than 60% of the patients would have to be screened but still 3952/6469, 67 (15.5%) MRSA carriers would have been missed. Screening of all emergency admissions to detect MRSA colonization is preferable to selective screening, relatively inexpensive, and might reduce the MRSA colonization rate of hospital-acquired MRSA and MRSA bacteraemia among emergency admissions.

Effect on MRSA transmission of rapid PCR testing of patients admitted to critical care

We report a significant reduction in the rate of meticillin-resistant Staphylococcus aureus (MRSA) transmission on a critical care unit when admission screening by culture was replaced with a same-day polymerase chain reaction (PCR) test. This was an observational cohort study, set in a 19-bed mixed medical and surgical adult critical care unit in southwest England. We studied 1305 patients admitted between April 2005 and February 2006. Standard MRSA culture methods were used to screen 612 patients between April 2005 and August 2005, and the IDI MRSA PCR test was used to screen 693 patients between September 2005 and February 2006. Standard infection control precautions were instituted when positive results were obtained by either method. Outcome measures included carriage rate, turnaround time for results and rate of subsequent MRSA transmission on the unit. The overall carriage rate on admission to the unit was 7.0%. Culture results were available in three working days, PCR results within one working day. The mean incidence of MRSA transmission was 13.89/1000 patient days during the culture phase and 4.9/1000 patient days during the PCR phase (relative risk reduction 0.65, 95% CI 0.28-1.07). PCR screening for MRSA on admission to critical care units is feasible in routine clinical practice, provides quicker results than culture-based screening and is associated with a significant reduction in subsequent MRSA transmission.

Evaluation of rapid screening and pre-emptive contact isolation for detecting and controlling methicillin-resistant Staphylococcus aureus in critical care: an interventional cohort study

INTRODUCTION

Rapid diagnostic tests may allow early identification of previously unknown methicillin-resistant Staphylococcus aureus (MRSA) carriers at intensive care unit (ICU) admission. The aim of this study was twofold: first, to assess whether a new molecular MRSA screening test can substantially decrease the time between ICU admission and identification of MRSA carriers; and, second, to examine the combined effect of rapid testing and pre-emptive contact isolation on MRSA infections.

METHOD

Since November 2003, patients admitted for longer than 24 hours to two adult ICUs were screened systematically on admission using quick, multiplex immunocapture-coupled PCR (qMRSA). Median time intervals from admission to notification of test results were calculated for a five-month intervention phase (November 2003-March 2004) and compared with a historical control period (April 2003-October 2003) by nonparametric tests. ICU-acquired MRSA infection rates were determined for an extended surveillance period (January 2003 through August 2005) and analyzed by Poisson regression methods.

RESULTS

During the intervention phase, 97% (450/462) of patients admitted to the surgical ICU and 80% (470/591) of patients admitted to the medical ICU were screened. On-admission screening identified the prevalence of MRSA to be 6.7% (71/1053). Without admission screening, 55 previously unknown MRSA carriers would have been missed in both ICUs. Median time from ICU admission to notification of test results decreased from 87 to 21 hours in the surgical ICU (P < 0.001) and from 106 to 23 hours in the medical ICU (P < 0.001). In the surgical ICU, 1,227 pre-emptive isolation days for 245 MRSA-negative patients were saved by using the qMRSA test. After adjusting for colonization pressure, the systematic on-admission screening and pre-emptive isolation policy was associated with a reduction in medical ICU acquired MRSA infections (relative risk 0.3, 95% confidence interval 0.1-0.7) but had no effect in the surgical ICU (relative risk 1.0, 95% confidence interval 0.6-1.7).

CONCLUSION

The qMRSA test decreased median time to notification from four days to one day and helped to identify previously unknown MRSA carriers rapidly. A strategy linking the rapid screening test to pre-emptive isolation and cohorting of MRSA patients substantially reduced MRSA cross-infections in the medical but not in the surgical ICU.