Community-associated meticillin-resistant Staphylococcus aureus: nosocomial transmission in a neonatal unit

Recombination-mediated dissemination of Methicillin-resistant S. aureus clonal complex 1 in the Egyptian health care settings

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a rapidly evolving pathogen that is frequently associated with outbreaks and sustained epidemics. This study investigated the population structure, resistome, virulome, and the correlation between antimicrobial resistance determinants with phenotypic resistance profiles of 36 representative hospital-acquired MRSA isolates recovered from hospital settings in Egypt.

RESULTS

The community-acquired MRSA lineage, clonal complex 1 (CC1) was the most frequently detected clone, followed by three other globally disseminated clones, CC121, CC8, and CC22. Most isolates carried SCCmec type V and more than half of isolates demonstrated multi-drug resistant phenotypes. Resistance to linezolid, a last resort antibiotic for treating multidrug resistant MRSA, was observed in 11.11% of the isolates belonging to different genetic backgrounds. Virulome analysis indicated that most isolates harboured a large pool of virulence factors and toxins. Genes encoding aureolysin, gamma hemolysins, and serine proteases were the most frequently detected virulence encoding genes. CC1 was observed to have a high pool of AMR resistance determinants including cfr, qacA, and qacB genes, which are involved in linezolid and quaternary ammonium compounds resistance, as well as high content of virulence-related genes, including both of the PVL toxin genes. Molecular clock analysis revealed that CC1 had the greatest frequency of recombination (compared to mutation) among the four major clones, supporting the role of horizontal gene transfer in modulating AMR and hypervirulence in this clone.

CONCLUSIONS

This pilot study provided evidence on the dissemination success of CA-MRSA clone CC1 among Egyptian hospitals. Co-detection of multiple AMR and virulence genes in this lineage pose a broad public health risk, with implications for successful treatment. The results of this study, together with other surveillance studies in Egypt, should be used to develop strategies for controlling MRSA infections in Egyptian health-care settings.

The Correlation Between Biofilm-Forming Ability of Community-Acquired Methicillin-Resistant Staphylococcus aureus Isolated from the Respiratory Tract and Clinical Characteristics in Children

Objective

This study aimed to investigate the biofilm-forming ability, molecular typing, and antimicrobial resistance of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) strains isolated from the respiratory tract of children and their correlation with clinical characteristics.

Methods

All CA-MRSA strains were isolated from hospitalized children, and their presentation, molecular typing, antimicrobial susceptibility, and biofilm formation were investigated. The clinical characteristics were compared between the strong and weak biofilm producer groups.

Results

Fifty-three CA-MRSA strains were isolated from the respiratory samples of 53 children, with nearly half of them being young infants (0-12 months). Approximately, 88.7% (47/53) of the isolates were resistant to four or more antibiotics, mainly β-lactam antibiotics, lincosamides, and macrolides. Twelve sequence types (STs) and 20 subtypes of staphylococcal protein A (spa) typing were identified, with ST59-t437 (39.6%, 21/53) as the predominant subtype. All strains showed the ability to form biofilms. When compared to children with weak biofilm-forming CA-MRSA strains, those with strong biofilm-forming strains had higher proportions of lower respiratory tract infections (LRTI) (88.5% vs 59.3%), obvious cough symptoms (84.6% vs 51.9%), and severe chest imaging manifestations (76.9% vs 37.0%). Furthermore, a strong biofilm-forming ability significantly increased the risk of prolonged cough in children with LRTI (44.4% vs 14.3%), and a positive correlation between the duration of cough and the extent of biofilm formation was observed. Medical history investigation revealed that the strong biofilm-forming group had a much higher percentage of macrolides intake than the weak biofilm-forming group in the last month before admission (61.5% vs 14.8%).

Conclusion

ST59-t437 was the most prevalent clone in CA-MRSA respiratory isolates among the hospitalized children. All CA-MRSA strains formed biofilms. The stronger the biofilm-forming ability, the more serious and prolonged were the respiratory symptoms.

Approaches for characterizing and tracking hospital-associated multidrug-resistant bacteria

Hospital-associated infections are a major concern for global public health. Infections with antibiotic-resistant pathogens can cause empiric treatment failure, and for infections with multidrug-resistant bacteria which can overcome antibiotics of "last resort" there exists no alternative treatments. Despite extensive sanitization protocols, the hospital environment is a potent reservoir and vector of antibiotic-resistant organisms. Pathogens can persist on hospital surfaces and plumbing for months to years, acquire new antibiotic resistance genes by horizontal gene transfer, and initiate outbreaks of hospital-associated infections by spreading to patients via healthcare workers and visitors. Advancements in next-generation sequencing of bacterial genomes and metagenomes have expanded our ability to (1) identify species and track distinct strains, (2) comprehensively profile antibiotic resistance genes, and (3) resolve the mobile elements that facilitate intra- and intercellular gene transfer. This information can, in turn, be used to characterize the population dynamics of hospital-associated microbiota, track outbreaks to their environmental reservoirs, and inform future interventions. This review provides a detailed overview of the approaches and bioinformatic tools available to study isolates and metagenomes of hospital-associated bacteria, and their multi-layered networks of transmission.

Whole-genome epidemiology, characterisation, and phylogenetic reconstruction of Staphylococcus aureus strains in a paediatric hospital

BACKGROUND

Staphylococcus aureus is an opportunistic pathogen and a leading cause of nosocomial infections. It can acquire resistance to all the antibiotics that entered the clinics to date, and the World Health Organization defined it as a high-priority pathogen for research and development of new antibiotics. A deeper understanding of the genetic variability of S. aureus in clinical settings would lead to a better comprehension of its pathogenic potential and improved strategies to contrast its virulence and resistance. However, the number of comprehensive studies addressing clinical cohorts of S. aureus infections by simultaneously looking at the epidemiology, phylogenetic reconstruction, genomic characterisation, and transmission pathways of infective clones is currently low, thus limiting global surveillance and epidemiological monitoring.

METHODS

We applied whole-genome shotgun sequencing (WGS) to 184 S. aureus isolates from 135 patients treated in different operative units of an Italian paediatric hospital over a timespan of 3 years, including both methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) from different infection types. We typed known and unknown clones from their genomes by multilocus sequence typing (MLST), Staphylococcal Cassette Chromosome mec (SCCmec), Staphylococcal protein A gene (spa), and Panton-Valentine Leukocidin (PVL), and we inferred their whole-genome phylogeny. We explored the prevalence of virulence and antibiotic resistance genes in our cohort, and the conservation of genes encoding vaccine candidates. We also performed a timed phylogenetic investigation for a potential outbreak of a newly emerging nosocomial clone.

RESULTS

The phylogeny of the 135 single-patient S. aureus isolates showed a high level of diversity, including 80 different lineages, and co-presence of local, global, livestock-associated, and hypervirulent clones. Five of these clones do not have representative genomes in public databases. Variability in the epidemiology is mirrored by variability in the SCCmec cassettes, with some novel variants of the type IV cassette carrying extra antibiotic resistances. Virulence and resistance genes were unevenly distributed across different clones and infection types, with highly resistant and lowly virulent clones showing strong association with chronic diseases, and highly virulent strains only reported in acute infections. Antigens included in vaccine formulations undergoing clinical trials were conserved at different levels in our cohort, with only a few highly prevalent genes fully conserved, potentially explaining the difficulty of developing a vaccine against S. aureus. We also found a recently diverged ST1-SCCmecIV-t127 PVL- clone suspected to be hospital-specific, but time-resolved integrative phylogenetic analysis refuted this hypothesis and suggested that this quickly emerging lineage was acquired independently by patients.

CONCLUSIONS

Whole genome sequencing allowed us to study the epidemiology and genomic repertoire of S. aureus in a clinical setting and provided evidence of its often underestimated complexity. Some virulence factors and clones are specific of disease types, but the variability and dispensability of many antigens considered for vaccine development together with the quickly changing epidemiology of S. aureus makes it very challenging to develop full-coverage therapies and vaccines. Expanding WGS-based surveillance of S. aureus to many more hospitals would allow the identification of specific strains representing the main burden of infection and therefore reassessing the efforts for the discovery of new treatments and clinical practices.

Staphylococcus aureus extracellular vesicles (EVs): surface-binding antagonists of biofilm formation

The prevalence of Staphylococcus aureus worldwide as a nosocomial infectious agent is recognized but the reason behind the spread of this bacterium has remained elusive. Here, we hypothesized that the communication of S. aureus might benefit from it blocking other bacteria from establishing themselves on the surface. This was found to be the case for several pathogens as the S. aureus supernatant curtailed their ability to form biofilms. Subsequent analyses using Acinetobacter baumannii as a model found this effect is primarily mediated by S. aureus' extracellular vesicles (EVs), which bound to the polystyrene surface. We found the EV-treated surfaces were significantly more hydrophilic after EV treatment, a condition that made it difficult for A. baumannii to initially adhere to the polystyrene surface and reduced its resulting biofilm by up to 93%. Subsequent tests found this also extended to several other bacterial pathogens, with a 40-70% decrease in their biofilm mass. The S. aureus EVs and their activity still remained after the surface was washed with 10% bleach, while the use of ethylenediaminetetraacetic acid (EDTA) removed both the EVs from the surface and their activity.

The recent emergence in hospitals of multidrug-resistant community-associated sequence type 1 and spa type t127 methicillin-resistant Staphylococcus aureus investigated by whole-genome sequencing: Implications for screening

Community-associated spa type t127/t922 methicillin-resistant Staphylococcus aureus (MRSA) prevalence increased from 1%-7% in Ireland between 2010–2015. This study tracked the spread of 89 such isolates from June 2013-June 2016. These included 78 healthcare-associated and 11 community associated-MRSA isolates from a prolonged hospital outbreak (H1) (n = 46), 16 other hospitals (n = 28), four other healthcare facilities (n = 4) and community-associated sources (n = 11). Isolates underwent antimicrobial susceptibility testing, DNA microarray profiling and whole-genome sequencing. Minimum spanning trees were generated following core-genome multilocus sequence typing and pairwise single nucleotide variation (SNV) analysis was performed. All isolates were sequence type 1 MRSA staphylococcal cassette chromosome mec type IV (ST1-MRSA-IV) and 76/89 were multidrug-resistant. Fifty isolates, including 40/46 from H1, were high-level mupirocin-resistant, carrying a conjugative 39 kb iles2-encoding plasmid. Two closely related ST1-MRSA-IV strains (I and II) and multiple sporadic strains were identified. Strain I isolates (57/89), including 43/46 H1 and all high-level mupirocin-resistant isolates, exhibited ≤80 SNVs. Two strain I isolates from separate H1 healthcare workers differed from other H1/strain I isolates by 7–47 and 12–53 SNVs, respectively, indicating healthcare worker involvement in this outbreak. Strain II isolates (19/89), including the remaining H1 isolates, exhibited ≤127 SNVs. For each strain, the pairwise SNVs exhibited by healthcare-associated and community-associated isolates indicated recent transmission of ST1-MRSA-IV within and between multiple hospitals, healthcare facilities and communities in Ireland. Given the interchange between healthcare-associated and community-associated isolates in hospitals, the risk factors that inform screening for MRSA require revision.

The changing face of community-acquired methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of infection, both in hospitalised patients with significant healthcare exposure and in patients without healthcare risk factors. Community-acquired methicillin-resistant S. aureus (CA-MRSA) are known for their rapid community transmission and propensity to cause aggressive skin and soft tissue infections and community-acquired pneumonia. The distinction between the healthcare-associated (HA)-MRSA and CA-MRSA is gradually fading owing to the acquisition of multiple virulence factors and genetic elements. The movement of CA-MRSA strains into the nosocomial setting limits the utility of using clinical risk factors alone to designate community or HA status. Identification of unique genetic characteristics and genotyping are valuable tools for MRSA epidemiological studies. Although the optimum pharmacotherapy for CA-MRSA infections has not been determined, many CA-MRSA strains remain broadly susceptible to several non-β-lactam antibacterial agents. This review aimed at illuminating the characteristic features of CA-MRSA, virulence factors, changing clinical settings and molecular epidemiology, insurgence into the hospital settings and therapy with drug resistance.

Molecular Characteristics of Disease-Causing and Commensal Staphylococcus lugdunensis Isolates from 2003 to 2013 at a Tertiary Hospital in Taiwan

Objectives

Staphylococcus lugdunensis can cause community- and healthcare-associated infections. This study investigated the molecular characteristics of S. lugdunensis isolates collected at our hospital and compared the characteristics of the infectious and commensal isolates.

Methods

We collected the S. lugdunensis isolates between 2003 and 2013. The antimicrobial resistance test, SCCmec typing, accessory gene regulator (agr) typing, pulsed-field gel electrophoresis (PFGE), and δ-like hemolysin activity were performed.

Results

In total, 118 S. lugdunensis isolates were collected, of which 67 (56.8%) were classified into the infection group and 51 (43.2%) into the commensal group. The oxacillin resistance rate was 36.4%. The most common SCCmec types were SCCmec types V (51.4%) and II (32.6%). In total, 34 pulsotypes were identified. The PFGE typing revealed five clones (pulsotypes A, J, M, N, and P) at our hospital. Pulsotypes A and N caused the spread of high oxacillin resistance. In total, 10.2% (12 of 118) of the isolates lacked δ-like hemolysin activity. Compared with the infection group, the commensal group showed a higher percentage of multiple drug resistance and carried a higher percentage of SCCmec type II (11 of 22, 50% and 3 of 21, 14.3%) and a lower percentage of SCCmec type V (8 of 22, 36.4% and 14 of 21, 66.7%). The commensal group (27 PFGE types) showed higher genetic diversity than did the infection group (20 PFGE types). No difference was observed in the distribution of the five main pulsotypes, agr typing, and the presence of δ-like hemolysin activity between the two groups.

Conclusions

Five main clones were identified at our hospital. The commensal group showed higher genetic diversity, had a higher percentage of multidrug resistance, and carried a higher percentage of SCCmec type II and a lower percentage of SCCmec type V than did the infection group.

Characterization of pediatric hospital-associated infection caused by methicillin-resistant Staphylococcus aureus in mainland China

BACKGROUND

This study was conducted to investigate the clinical features of hospital-associated infections (HAIs) caused by methicillin-resistant Staphylococcus aureus (MRSA) in Chinese children, and the molecular characteristics of the bacteria.

METHODS

Patients with HAIs caused by MRSA were identified retrospectively. All isolates were analyzed using molecular typing and antimicrobial susceptibility tests.

RESULTS

In total, 150 patients were identified, with a median age of 18 months. The most common infection was pneumonia (55.3%), followed by skin and soft tissue infections (46%). Invasive infections were observed in 52 patients (34.7%), and their hospital stay was longer compared with non-invasive cases (21 vs 12 days, p = 0.047). A total of 16 sequence types (STs) were identified. ST239 and ST59 were common clones, accounting for 46% and 28% of cases, respectively. Compared with cases caused by ST239-SCCmecI-III, patients infected by ST59-SCCmecIV-V had a lower median age (11 vs 41 months, p = 0.047) and more commonly developed invasive infection (50% vs 18.8%, p = 0.006).

CONCLUSIONS

Invasive infections accounted for a large proportion of HAIs caused by MRSA. ST59-SCCmecIV/V, a common clone in the community, caused HAIs in Chinese children, more often infected younger children and caused invasive infections.

[Update on outbreaks reported from neonatal intensive care units (2010-203): Staphylococcus aureus]

In terms of the unique risk profile of the patients and the morbidity associated with S. aureus infections in this vulnerable patient population, the literature on outbreaks of S. aureus (including MRSA) in neonatal intensive care units (NICUs) needs to be analyzed separately from reports derived from other intensive care units. With the objective of updating important information for those involved in outbreak management and fostering preventive efforts, this article summarizes the results of a systematic literature analysis, referring to an earlier publication by Gastmeier et al. It focuses on NICU outbreaks caused by S. aureus (including MRSA) and on controlling them.

Active Surveillance and Decolonization of Methicillin-Resistant Staphylococcus aureus on Admission to Neonatal Intensive Care Units in Hong Kong: A Cost-Effectiveness Analysis

Objective.

To examine potential clinical outcomes and cost of active methicillin-resistant Staphylococcus aureus (MRSA) surveillance with and without decolonization in neonatal intensive care units (NICUs) from the perspective of healthcare providers in Hong Kong.

Design.

Decision analysis modeling.

Setting.

NICU.

Patients.

Hypothetical cohort of patients admitted to an NICU.

Methods.

We designed a decision tree to simulate potential outcomes of active MRSA surveillance with and without decolonization in patients admitted to an NICU. Outcome measures included total direct medical cost per patient, MRSA infection rate, and MRSA-associated mortality rate. Model inputs were derived from the literature. Sensitivity analyses evaluated the impact of uncertainty in all model variables.

Results.

In the base-case analysis, active surveillance plus decolonization showed a lower expected MRSA infection rate (0.911% vs 1.759%), MRSA-associated mortality rate (0.223% vs 0.431%), and total cost per patient (USD 47,294 vs USD 48,031) compared with active surveillance alone. Sensitivity analyses showed that active surveillance plus decolonization cost less and had lower event rates if the incidence risk ratio of acquiring MRSA infections in carriers after decolonization was less than 0.997. In 10,000 Monte Carlo simulations, active surveillance plus decolonization was significantly less costly than active surveillance alone 99.9% of the time, and both the MRSA infection rate and the MRSA-associated mortality rate were significantly lower 99.9% of the time.

Conclusions.

Active surveillance plus decolonization for patients admitted to NICUs appears to be cost saving and effective in reducing the MRSA infection rate and the MRSA-associated mortality rate if addition of decolonization to active surveillance reduces the risk of MRSA infection.

Infect Control Hosp Epidemiol 2012;33(10):1024-1030

Community-associated methicillin-resistant Staphylococcus aureus case studies

Over the past decade, the emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has changed the landscape of S. aureus infections around the globe. Initially recognized for its ability to cause disease in young and healthy individuals without healthcare exposures as well as for its distinct genotype and phenotype, this original description no longer fully encompasses the diversity of CA-MRSA as it continues to expand its niche. Using four case studies, we highlight a wide range of the clinical presentations and challenges of CA-MRSA. Based on these cases we further explore the globally polygenetic background of CA-MRSA with a special emphasis on generally less characterized populations.

First outbreak with MRSA in a Danish neonatal intensive care unit: risk factors and control procedures

Introduction

The purpose of the study was to describe demographic and clinical characteristics and outbreak handling of a large methicillin-resistant Staphylococcus aureus (MRSA) outbreak in a neonatal intensive care unit (NICU) in Denmark June 25^th–August 8^th 2008, and to identify risk factors for MRSA transmission.

Methods

Data were collected retrospectively from medical records and the Danish Neobase database. All MRSA isolates obtained from neonates, relatives and NICU health care workers (HCW) as well as environmental cultures were typed.

Results

During the 46 day outbreak period, 102 neonates were admitted to the two neonatal wards. Ninety-nine neonates were subsequently sampled, and 32 neonates (32%) from 25 families were colonized with MRSA (spa-type t127, SCCmec V, PVL negative). Thirteen family members from 11 of those families (44%) and two of 161 HCWs (1%) were colonized with the same MRSA. No one was infected. Five environmental cultures were MRSA positive. In a multiple logistic regression analysis, nasal Continuous Positive Airway Pressure (nCPAP) treatment (p = 0.006) and Caesarean section (p = 0.016) were independent risk factors for MRSA acquisition, whereas days of exposure to MRSA was a risk factors in the unadjusted analysis (p = 0.04).

Conclusions

MRSA transmission occurs with high frequency in the NICU during hospitalization with unidentified MRSA neonates. Caesarean section and nCPAP treatment were identified as risk factors for MRSA colonization. The MRSA outbreak was controlled through infection control procedures.

Diversity of methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from inpatients of 30 hospitals in Orange County, California

There is a need for a regional assessment of the frequency and diversity of MRSA to determine major circulating clones and the extent to which community and healthcare MRSA reservoirs have mixed. We conducted a prospective cohort study of inpatients in Orange County, California, systematically collecting clinical MRSA isolates from 30 hospitals, to assess MRSA diversity and distribution. All isolates were characterized by spa typing, with selective PFGE and MLST to relate spa types with major MRSA clones. We collected 2,246 MRSA isolates from hospital inpatients. This translated to 91/10,000 inpatients with MRSA and an Orange County population estimate of MRSA inpatient clinical cultures of 86/100,000 people. spa type genetic diversity was heterogeneous between hospitals, and relatively high overall (72%). USA300 (t008/ST8), USA100 (t002/ST5) and a previously reported USA100 variant (t242/ST5) were the dominant clones across all Orange County hospitals, representing 83% of isolates. Fifteen hospitals isolated more t008 (USA300) isolates than t002/242 (USA100) isolates, and 12 hospitals isolated more t242 isolates than t002 isolates. The majority of isolates were imported into hospitals. Community-based infection control strategies may still be helpful in stemming the influx of traditionally community-associated strains, particularly USA300, into the healthcare setting.

Recurrent furunculosis: a review of the literature

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is increasing in incidence and manifests as skin and soft tissue infections including furuncles. The majority of studies have focused on the epidemiology of single furuncles and not recurrent disease. There is a lack of data concerning the incidence of furunculosis outside the U.S.A.

OBJECTIVES

This report reviews the literature of recurrent furunculosis and the impact of CA-MRSA on the disease.

METHODS

Article citations were searched within PubMed. Search terms used were 'furunculosis', 'recurrent furunculosis', 'skin abscess' and 'recurrent boils'. Articles were discarded if they did not refer to furunculosis secondary to S. aureus.

RESULTS

A total of 1515 articles were initially retrieved with the term 'furunculosis', 77 with the term 'recurrent furunculosis', 2778 with the term 'skin abscess', and 1526 with the term 'recurrent boils'. After excluding articles not referring to S. aureus furunculosis, 86 articles were included for this review.

CONCLUSIONS

Furunculosis is increasing within the U.S.A. secondary to the CA-MRSA epidemic and the resistant organism's close association with the Panton-Valentine leucocidin (PVL) virulence factor. PVL is associated with follicular infections in general, having its strongest association with furunculosis and its recurrence. The majority of furuncles in the U.S.A. are caused by CA-MRSA, while elsewhere in the world they are caused by methicillin-sensitive S. aureus. Nasal carriage of S. aureus is the primary risk factor for recurrent furunculosis and occurs in 60% of individuals.

Meticillin-resistant Staphylococcus aureus in elderly residents of care homes: colonization rates and molecular epidemiology

BACKGROUND

Meticillin-resistant Staphylococcus aureus (MRSA) is a significant cause of mortality and morbidity in healthcare and community settings; however, there is a paucity of large-scale, longitudinal studies monitoring the occurrence of MRSA in the care home setting.

AIM

To determine the molecular epidemiology of MRSA colonizing elderly residents of care homes.

METHODS

Residents in 65 care homes in Leeds, UK, were screened for MRSA nasal colonization in four consecutive years (2006-2009). Isolates were characterized using antibiotic susceptibility testing, detection of the Panton-Valentine leucocidin (PVL) locus, accessory gene regulator allotyping, characterization of the staphylococcal cassette chromosome mec element, spa-typing and pulsed-field gel electrophoresis.

FINDINGS

MRSA was recovered from 888 nasal swabs of 2492 residents and prevalence was similar (19-22%) throughout the study. Resistance to ≥3 antibiotic classes was common (34%), but resistance to only β-lactam agents was rare (3%); no PVL-positive isolates were identified. Most isolates were related to healthcare-associated epidemic-MRSA type 15 (EMRSA-15, ST22-IV); such isolates decreased in prevalence during the study (86-72%; P < 0.0001, χ(2)-test). The remainder belonged to five different multi-locus sequence type clonal complexes (CC). Most notably, CC59 strains increased in prevalence (10-25%; P < 0.0001, χ(2)-test) and were associated with high-level mupirocin resistance.

CONCLUSIONS

The molecular epidemiology of MRSA in care homes is complex and dynamic. There was a high, consistent prevalence of MRSA nasal colonization, dominated by healthcare-associated strains. Vigilance is recommended; however, as high-level mupirocin resistance was associated with a single clonal group (CC59) that significantly increased in prevalence during the study.

Community-associated meticillin-resistant Staphylococcus aureus carriage in hospitalized patients in tropical northern Australia

BACKGROUND

Community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) was first reported in remote Australian Aboriginal communities. It is a prominent clinical pathogen in northern Australia with potential for transmission within the local hospital setting.

AIM

To determine epidemiological characteristics of S. aureus carriage within the Royal Darwin Hospital.

METHODS

We screened two patient groups: an 'admission group' recruited within 48 h of admission; and an 'inpatient group' recruited five or more days after admission. S. aureus isolates were characterized by antibiotic susceptibility testing and genotyped by a multi-locus sequence type-based high-resolution melting scheme.

FINDINGS

S. aureus carriage on admission was 30.7% of 225 compared with 34.8% among 201 inpatients, with MRSA carriage of 2.2% and 18.9% respectively. We isolated CA-MRSA from 0.9% and 10.4%, and healthcare-associated (HCA)-MRSA from 1.3% and 9.0% of the admission and inpatient groups, respectively. Among the inpatient group, hospital-associated ST239 was the most common MRSA strain. CA-MRSA was represented by one clonal complex (CC) in the admission group (CC5) and seven CCs in the inpatient group (CC1, 93, 5, 6, 30, 75, 88).

CONCLUSION

Inpatient carriage of multiple CA-MRSA lineages suggests selection for and transmission within the hospital of not only typical HCA-MRSA, but also diverse CA-MRSA strains.

Changing epidemiology of methicillin-resistant Staphylococcus aureus colonization in paediatric intensive-care units

Community-associated methicillin-resistant S. aureus (CA-MRSA) accounts for a growing proportion of hospital-onset infections, and colonization is a risk factor. This study aimed to determine changes in the prevalence of CA-MRSA colonization in paediatric intensive-care units (ICUs). A total of 495 paediatric patients colonized with MRSA from neonatal, medical, surgical, and cardiac ICUs between 2001 and 2009 were identified. Isolates were characterized by spa type, staphylococcal cassette chromosome (SCC) mec type and the presence of the genes encoding Panton–Valentine leukocidin (PVL). The proportion of patients colonized with MRSA remained stable (average 3·2%). The proportion of isolates with spa type 1, SCCmec type IV and PVL increased over time to maximums in 2009 of 36·1% (P < 0·001), 54·2% (P = 0·03) and 28·9% (P = 0·003), respectively. Antibiotic susceptibility patterns showed increasing proportions susceptible to clindamycin, gentamicin, tetracycline and trimethoprim-sulfamethoxazole (P values <0·001). In conclusion, the proportion of MRSA-colonized children in ICUs with CA-MRSA increased significantly over time.

The use of high-resolution melting analysis for rapid spa typing on methicillin-resistant Staphylococcus aureus clinical isolates

Methicillin-resistant Staphylococcus aureus (MRSA) has been endemic in Hong Kong for three decades. This study evaluated the practical use of high-resolution melting (HRM) real-time PCR analysis on MRSA staphylococcal Protein A (spa) typing on local MRSA isolates. Among 55 clinical MRSA isolates collected in 2011, 12 different spa types were observed by the conventional PCR-sequencing method including the locally predominant spa type t1081 and two locally predominant community acquired MRSA spa types t019 and t437. By using the HRM method, it could differentiate all 12 spa genotypes by distinct melting curves and HRM difference plot analysis. These two methods demonstrated 100% concordance whereas the HRM method required only 3h of turnaround time and one-fifth of reagent cost compared to the conventional method. Our study confirmed that the cost effective and rapid HRM typing approach is practically useful for MRSA community transmission monitoring and nosocomial outbreak control in Hong Kong.

Epidemic spread of ST1-MRSA-IVa in a neonatal intensive care unit, Italy

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has recently emerged as an important pathogen in neonatal intensive care units (NICUs). The purposes of this study were to characterize methicillin-resistant isolates from an outbreak in a NICU, to examine the genetic traits and clonality of CA-MRSA, and to review the characteristics and outcomes of the neonatal cases and investigate the routes of entry and transmission of the MRSA outbreak strain in the NICU under study.

METHODS

The study NICU practiced an active surveillance program for multidrug-resistant organisms, including weekly cultures for detection of MRSA from nasal swabs among all the admitted neonates. All first isolates from surveillance cultures and all clinical isolates were submitted for susceptibility testing and genotyping. Data from each infant's medical records were prospectively included in a database, and the clinical features and outcomes of the colonized/infected infants were assessed.

RESULTS

A total of 14 infants were colonized or infected by a strain of ST1-MRSA-IVa between April and August 2011. The CA-MRSA strain appeared to have been introduced to the NICU by an infected infant transferred from another hospital. The outbreak was successfully contained by multifaceted infection control interventions.

CONCLUSIONS

The results of this study confirm that NICU is a healthcare setting with a critical permeability to CA-MRSA. Active surveillance including molecular typing can help to detect and monitor the spread of antimicrobial drug-resistant organisms, and thus trigger timely control interventions.

Putative link between Staphylococcus aureus bacteriophage serotype and community association

Methicillin-resistant Staphylococcus aureus (MRSA) from humans can be broadly separated into 3 groups: healthcare-associated (HA), community-associated (CA), and livestock-associated (LA) MRSA. Initially based on epidemiological features, division into these classes is becoming increasingly problematic. The sequencing of S. aureus genomes has highlighted variations in their accessory components, which likely account for differences in pathogenicity and epidemicity. In particular, temperate bacteriophages have been regarded as key players in bacterial pathogenesis. Bacteriophage-associated Panton-Valentine leukocidin genes (luk-PV) are regarded as epidemiological markers of the CA-MRSA due to their high prevalence in CA strains. This paper describes the development and application of a partial composite S. aureus virulence-associated gene microarray. Epidemic, pandemic, and sporadic lineages of UK HA and CA S. aureus were compared. Phage structural genes linked with CA isolates were identified and in silico analysis revealed these to be correlated with phage serogroup. CA strains predominantly carried a PVL-associated phage either of the A or Fb serogroup, whilst HA strains predominantly carried serogroup Fa or B phages. We speculate that carriage of a serogroup A/Fb PVL-associated phage rather than the luk-PV genes specifically is correlated with CA status.

Methicillin-resistant Staphylococcus aureus colonization among women admitted for preterm delivery

OBJECTIVE

Methicillin-resistant Staphylococcus aureus infection is associated with morbidity in the neonatal intensive care unit. The purpose of this study was to determine the relationship between preterm maternal methicillin-resistant S aureus colonization and subsequent colonization and infection in premature neonates.

STUDY DESIGN

We conducted a prospective cohort study of 422 women admitted for preterm delivery. Methicillin-resistant S aureus cultures were collected from mothers and their neonates admitted to neonatal intensive care unit. We determined the proportion of women and neonates colonized with methicillin-resistant S aureus and examined possible factors associated with colonization and infection.

RESULTS

Fifteen of 422 (3.6%) women were found to be colonized with methicillin-resistant S aureus. Thirteen of 212 (6.1%) neonates admitted to neonatal intensive care unit were methicillin-resistant S aureus colonized and 3 of 13 (23.1%) developed a methicillin-resistant S aureus infection. We identified 1 methicillin-resistant S aureus colonized maternal-neonatal pair. The infant became methicillin-resistant S aureus positive 30 days after admission and did not develop a methicillin-resistant S aureus infection.

CONCLUSION

These findings suggest that maternal methicillin-resistant S aureus colonization is not a significant risk factor for vertical transmission of neonatal methicillin-resistant S aureus colonization.

Multilocus sequence typing of total-genome-sequenced bacteria

Accurate strain identification is essential for anyone working with bacteria. For many species, multilocus sequence typing (MLST) is considered the "gold standard" of typing, but it is traditionally performed in an expensive and time-consuming manner. As the costs of whole-genome sequencing (WGS) continue to decline, it becomes increasingly available to scientists and routine diagnostic laboratories. Currently, the cost is below that of traditional MLST. The new challenges will be how to extract the relevant information from the large amount of data so as to allow for comparison over time and between laboratories. Ideally, this information should also allow for comparison to historical data. We developed a Web-based method for MLST of 66 bacterial species based on WGS data. As input, the method uses short sequence reads from four sequencing platforms or preassembled genomes. Updates from the MLST databases are downloaded monthly, and the best-matching MLST alleles of the specified MLST scheme are found using a BLAST-based ranking method. The sequence type is then determined by the combination of alleles identified. The method was tested on preassembled genomes from 336 isolates covering 56 MLST schemes, on short sequence reads from 387 isolates covering 10 schemes, and on a small test set of short sequence reads from 29 isolates for which the sequence type had been determined by traditional methods. The method presented here enables investigators to determine the sequence types of their isolates on the basis of WGS data. This method is publicly available at www.cbs.dtu.dk/services/MLST.

Emergence of hospital- and community-associated panton-valentine leukocidin-positive methicillin-resistant Staphylococcus aureus genotype ST772-MRSA-V in Ireland and detailed investigation of an ST772-MRSA-V cluster in a neonatal intensive care unit

Sequence type 22 (ST22) methicillin-resistant Staphylococcus aureus (MRSA) harboring staphylococcal cassette chromosome mec (SCCmec) IV (ST22-MRSA-IV) has predominated in Irish hospitals since the late 1990s. Six distinct clones of community-associated MRSA (CA-MRSA) have also been identified in Ireland. A new strain of CA-MRSA, ST772-MRSA-V, has recently emerged and become widespread in India and has spread into hospitals. In the present study, highly similar MRSA isolates were recovered from seven colonized neonates in a neonatal intensive care unit (NICU) in a maternity hospital in Ireland during 2010 and 2011, two colonized NICU staff, one of their colonized children, and a NICU environmental site. The isolates exhibited multiantibiotic resistance, spa type t657, and were assigned to ST772-MRSA-V by DNA microarray profiling. All isolates encoded resistance to macrolides [msr(A) and mpb(BM)] and aminoglycosides (aacA-aphD and aphA3) and harbored the Panton-Valentine leukocidin toxin genes (lukF-PV and lukS-PV), enterotoxin genes (sea, sec, sel, and egc), and one of the immune evasion complex genes (scn). One of the NICU staff colonized by ST772-MRSA-V was identified as the probable index case, based on recent travel to India. Seven additional hospital and CA-ST772-MRSA-V isolates recovered from skin and soft tissue infections in Ireland between 2009 and 2011 exhibiting highly similar phenotypic and genotypic characteristics to the NICU isolates were also identified. The clinical details of four of these patients revealed connections with India through ethnic background or travel. Our study indicates that hospital-acquired and CA-ST772-MRSA-V is currently emerging in Ireland and may have been imported from India on several occasions.

Characteristics of Invasive Staphylococcus aureus in United Kingdom Neonatal Units

BACKGROUND

In industrialized countries, Staphylococcus aureus (SA) is a leading cause of late-onset neonatal sepsis.

METHODS

Culture-proven episodes were identified prospectively from neonatal units participating in the neonatal infection surveillance network. Demographic, risk factor, and outcome data were collected.

RESULTS

Between 2004 and 2009, there were 117 episodes of SA infections (including 8 methicillin-resistant SA) in 116 infants from 13 units. The median gestational age and birth-weight were 27 weeks (90% ≤ 37 weeks, 85% ≤ 32 weeks) and 850 g (90% ≤ 2500 g), respectively. The overall incidence was 0.6 per 1000 live births and 23/1000 in infants <1500 g. Most episodes (94%) occurred more than 48 hours after birth (late onset). There were 7 early-onset episodes (< 48 hours) (median gestational age, 38.5 weeks), all due to methicillin-susceptible SA. At the time of culture, 67 of 95 (71%) infants were receiving respiratory support and 47 of 94 (50%) had a central line in situ. The majority of infants had nonspecific clinical features although evidence of focal infection (skin, soft tissue, bone, joint, or pneumonia) was ultimately seen in 41 of 91 (45%). There were 18 deaths, 4 (all late onset) directly due to methicillin-susceptible SA sepsis (4.4%).

CONCLUSIONS

SA is the second most common pathogen causing late-onset neonatal infections in this neonatal network. Infants who weigh < 1500 g in intensive care settings are the most vulnerable group. Clinical signs are not sufficiently distinctive to allow targeted therapy, suggesting that an antistaphylococcal agent should be part of empiric therapy for late-onset sepsis in premature infants.

Community-associated meticillin-resistant Staphylococcus aureus strains as a cause of healthcare-associated infection

Community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) was first noticed as a cause of infection in community-based individuals without healthcare contact. As the global epidemic of CA-MRSA has continued, CA-MRSA strain types have begun to emerge as a cause of healthcare-associated infections (HAIs) and hospital outbreaks have occurred worldwide. In areas where CA-MRSA clones have become established with high prevalence, for example USA300 (ST8-IV) in the USA, CA-MRSA are beginning to supplant or overtake traditional healthcare-associated MRSA strains as causes of HAI. The emergence of CA-MRSA as a cause of HAI puts a wider group of hospitalised patients, healthcare workers and their community contacts potentially at risk of MRSA infection. It also exposes CA-MRSA strains to the selective pressure of antibiotic use in hospitals, potentially resulting in increased antibiotic resistance, challenges traditional definitions of CA-MRSA and hampers control efforts due to the constant re-introduction of MRSA from an emerging community reservoir. There is thus an urgent need to clarify the definitions, prevalence and epidemiology of CA-MRSA and to develop systems for the identification and control of these organisms in the community, in hospitals and other healthcare facilities, and at the community-hospital interface.

Active surveillance culturing impacts methicillin-resistant Staphylococcus aureus acquisition in a pediatric intensive care unit

OBJECTIVE

To determine whether active surveillance culturing for methicillin-resistant Staphylococcus aureus (MRSA) decreases nosocomial MRSA acquisition in the pediatric intensive care unit.

DESIGN

Before and after observational study.

SETTING

A tertiary care, 20-bed, pediatric intensive care unit.

PATIENTS

All patients admitted to the pediatric intensive care unit.

INTERVENTIONS

Anterior nares cultures for MRSA were obtained on admission and weekly in the pediatric intensive care unit from January 2007 to December 2009 as part of a hospital quality improvement project.

MEASUREMENTS AND MAIN RESULTS

MRSA admission prevalence and nosocomial incidence density were determined retrospectively for 2006 and prospectively for 2007-2009. Nosocomial MRSA incidence density during the intervention period was determined monthly and analyzed by trend analysis by using a general linear model. The correlation of active surveillance culturing compliance with nosocomial acquisition of MRSA was analyzed. Possible confounding by healthcare worker hand hygiene compliance observed during the intervention period was also analyzed by multivariate linear regression analysis. The yearly MRSA incidence density significantly decreased from 2006 to 2009 (6.88 per 1,000 patient days to 1.45 per 1,000 patient days, p < .001) and from 2007 to 2009 (7.32 per 1,000 patient days to 1.45 per 1,000 patient days, p < .001). Trend analysis demonstrated a significant decline in MRSA acquisition over time following the introduction of active surveillance culturing (p < .001). Surveillance culturing was significantly associated with the decline in MRSA acquisition observed in the pediatric intensive care unit by multivariate regression analysis when controlling for hand hygiene (p = .01).

CONCLUSIONS

Active surveillance culturing resulted in significantly decreased nosocomial acquisition of MRSA in a pediatric intensive care unit setting. Admission and weekly active surveillance culturing appears to be an effective tool to decrease the spread of MRSA in the pediatric intensive care unit, independent of improvement in hand hygiene compliance. The impact on hospital-acquired MRSA infections and the cost benefit of active surveillance culturing require further study.

A review of hand-washing techniques in primary care and community settings

AIM

This review seeks to identify the most effective hand-washing and hand-cleansing practice that could be used in primary care.

BACKGROUND

Healthcare associated infection is a major problem in the UK causing 5000 deaths every year. Current guidelines indicate expert opinion is the level of evidence for hand washing as an activity to reduce infection.

DESIGN

Systematic review.

METHOD

Publications on hand-washing, hand-cleansing studies, policy and practice-based documents were sought by searching several databases. Terms used included hand washing, hand cleansing, hand hygiene, hand decontamination, infection control and primary care.

RESULTS

Few articles described the hand-washing technique in detail and some publications simply referred to either the European and British Standards or the Centre for Disease Control statement on hand washing. Major discrepancies in hand position and water flow direction were found. Several methodological problems were also identified and few studies were undertaken in primary care.

CONCLUSION

This review has found a lack of evidence for hand-washing techniques being undertaken in practice today. Findings from hand-washing technique studies were inconclusive and methodological issues exist resulting in sparse reliable evidence. There is an urgent need to undertake methodologically sound studies of hand-washing techniques for use in the ever expanding scope of primary care practice.

RELEVANCE TO CLINICAL PRACTICE

Evidence for hand-washing and hand-cleansing techniques will inform healthcare professional practice, and contribute to the overall management of infection control in primary care.

Synthesis and structure activity relationship studies of novel Staphylococcus aureus Sortase A inhibitors

Synthetic methods have been developed for lead Sortase A inhibitors identified from previous studies. Several derivatives of the lead inhibitor were synthesized to derive preliminary structure activity relationships (SAR). Different regions of the lead inhibitor that are critical for the enzyme activity have been determined by systematic SAR studies. The E stereochemistry of the lead compound was found to be critical for its activity. Replacement of the E double bond with Z double bond or a rigid triple bond reduced the enzyme inhibitory activity in most cases. Reduction of the double bond to a C-C single bond resulted in complete loss of activity. Amide carbonyl and NH groups were also found to be crucial for the activity of this class of inhibitors, as well. The morpholine ring oxygen atom was also found to be an important factor for the activity of the lead inhibitor. Preliminary SAR studies led to the identification of compounds with improved enzyme inhibition. The most active compound was found to have an IC(50) value of 58 microM against the enzyme.

Changes in the molecular epidemiological characteristics of methicillin-resistant Staphylococcus aureus in a neonatal intensive care unit

OBJECTIVE

To determine whether the molecular epidemiological characteristics of methicillin-resistant Staphylococcus aureus (MRSA) had changed in a level III neonatal intensive care unit (NICU).

DESIGN

Retrospective review of medical records.

SETTING

Level III NICU of a university-affiliated children's hospital in New York, New York.

PATIENTS

Case patients were neonates hospitalized in the NICU who were colonized or infected with MRSA.

METHODS

Rates of colonization and infection with MRSA during the period from 2000 through 2008 were assessed. Staphylococcal chromosomal cassette (SCC) mecA analysis and genotyping for S. aureus encoding protein A (spa) were performed on representative MRSA isolates from each clonal pulsed-field gel electrophoresis pattern.

RESULTS

Endemic MRSA infection and colonization occurred throughout the study period, which was punctuated by 4 epidemiologic investigations during outbreak periods. During the study period, 93 neonates were infected and 167 were colonized with MRSA. Surveillance cultures were performed for 1,336 neonates during outbreak investigations, and 115 (8.6%) neonates had MRSA-positive culture results. During 2001-2004, healthcare-associated MRSA clones, carrying SCC mec type II, predominated. From 2005 on, most MRSA clones were community-associated MRSA with SCC mec type IV, and in 2007, USA300 emerged as the principal clone.

CONCLUSIONS

Molecular analysis demonstrated a shift from healthcare-associated MRSA (2001-2004) to community-associated MRSA (2005-2008).

Community-associated methicillin-resistant Staphylococcus aureus (MRSA): an overview for nurses

Upon completion of this activity, the learner will be able to:1. Differentiate between the two types of Methicillin-resistant Staphylococcus aureus (MRSA)--HA-MRSA and CA-MRSA. 2. Describe evidence-based management of MRSA infections. 3. Describe the epidemiology and clinical manifestations of MRSA infections.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

First outbreak of PVL-positive nonmultiresistant MRSA in a neonatal ICU in Australia: comparison of MALDI-TOF and SNP-plus-binary gene typing

The purpose of this brief report is to describe the first outbreak of a community-associated nonmultiresistant and PVL-positive MRSA strain (CC30) in a neonatal intensive care unit in Australia. The utility of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) for microbial typing is compared with single nucleotide polymorphism (SNP) plus binary gene analysis. The composite correlation index analysis of the MALDI-TOF-MS data demonstrated the similar inter-strain relatedness found with the SNP-plus-binary gene typing used to confirm the outbreak. The evolving spread of MRSA emphasizes the importance of surveillance, infection control vigilance and the ongoing investigation of rapid typing methods for MRSA.

Clinical, molecular and epidemiological description of a cluster of community-associated methicillin-resistant Staphylococcus aureus isolates from injecting drug users with bacteraemia

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is an increasing problem, predominantly in previously healthy individuals including notable risk groups such as the homeless, those who play close-contact sports, military personnel, men who have sex with men (MSM) and injecting drug users (IDUs). Over a 5-month period, four IDUs were admitted to Addenbrooke's Hospital, Cambridge, UK, with MRSA bacteraemia. All four patients presented with complex clinical features, with more than one focus of infection, and were linked epidemiologically. The atypical antibiogram of the MRSA isolates (ciprofloxacin-susceptible) prompted further characterization, both phenotypically (antibiotic resistance typing; phage typing) and genotypically (detection of toxin genes by PCR; pulsed-field gel electrophoresis (PFGE); Staphylococcal chromosome cassette (SCC) mec typing; multi-locus sequence typing (MLST)). All four isolates had similar antibiograms, were Panton-Valentine Leucocidin (PVL) toxin gene-negative, harboured SCCmec type IV and were closely related as shown by phage typing and PFGE. These isolates were representatives of a community-associated clone, ST1-MRSA-IV, known to be circulating in IDUs in the UK since 2001. This paper presents a detailed description of the clinical, microbiological and epidemiological features of a series of CA-MRSA bacteraemias in IDUs in the UK.

An investigation of the risk factors for infection with methicillin-resistant Staphylococcus aureus among patients in a neonatal intensive care unit

BACKGROUND

The aims of this study were to investigate the risk factors of methicillin-resistant Staphylococcus aureus (MRSA) infection among infants to establish effective infection control measures for neonatal intensive care unit (NICU).

METHODS

Data were prospectively collected from 961 infants hospitalized in a teaching hospital in Japan, from July 2002 through December 2005.

RESULTS

Among all infants, 28 (2.9%) developed MRSA infections. Multivariate logistic regression analyses demonstrated the risk factors for developing MRSA infections to include a low birth weight (odds ratio [OR], 0.91; 95% confidence interval [CI]: 0.93-0.99), the presence of eye mucous (OR, 6.78; 95% CI: 2.87-16.01), the practice of kangaroo mother care (OR, 3.82; 95% CI: 1.11-13.13), and the MRSA colonization rate (OR, 11.12; 95% CI: 1.32-93.89).

CONCLUSION

The risk factors for developing a MRSA infection among infants in NICU were a low birth weight, the presence of eye mucous, the practice of kangaroo mother care, and a high MRSA colonization rate. Therefore, extra attention should be given to infants in high-risk groups demonstrating a low birth weight and the presence of eye mucous and who have undergone kangaroo mother care. As a result, the cohort isolation of infants with MRSA may therefore be an effective strategy to prevent MRSA infections.

One tube multiplex PCR for simple screening of SCCmec I-V types of methicillin-resistant Staphylococcus aureus

In this study, a rapid and simple one-tube multiplex PCR (M-PCR) method was developed for Staphylococcal Cassette Chromosome mec (SCCmec), primary screening. One hundred and eight methicillin-resistant Staphylococcus aureus (MRSA) isolates with SCC mec typing results using the Oliveira and de Lencastre method (Oliveira and de Lencastre. Antimicrob. Agents Chemother. 46:2155-2161, 2002), were evaluated for the efficacy of our method. Typing results were also compared to the recently published PCR protocol by Kondo et al., (Kondo et al., Antimicrob Agents Chemother. 51:264-74, 2007). The one-tube M-PCR method showed comparable efficacy to the other two methods. None of the isolates were classified as non-typable in Kondo's and our method. Two formerly assigned SCCmec type I isolates by Oliveira and de Lencastre were determined as SCCmec type IV by Kondo's and the method in this study. In conclusion, the one-tube M-PCR method developed in this study increased the rapidity and simplicity for primary screening SCCmec type I to V MRSA.

Report of a hospital neonatal unit outbreak of community-associated methicillin-resistantStaphylococcus aureus

Community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA) with the type IV staphylococcal chromosomal cassettemec(SCCmec) is rarely reported as being acquired in hospital. We report a hospital outbreak, in Grampian, Scotland, of eight cases of skin and soft-tissue infections due to such a strain. All patients had been in the labour, delivery and maternity units of a small community hospital during a 7-month period. Typing by pulsed-field gel electrophoresis showed the isolates to be a single strain closely related to the USA800 lineage (paediatric clone) and additional typing confirmed it as ST5-MRSA-IV. Genes for exfoliative toxin A (ETA) and enterotoxin D were detected by PCR in all the isolates although none carried the Panton–Valentine leukocidin gene. Region-wide surveillance of over 6000 MRSA isolates collected from 1998 to 2004 showed that 95 (1·6%) were closely related to the outbreak strain although only 60 carried the ETA gene. The strain has not been seen elsewhere in Scotland.

Differences between "classical" risk factors for infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and risk factors for nosocomial bloodstream infections caused by multiple clones of the staphylococcal cassette chromosome mec type IV MRSA strain

OBJECTIVE

To identify risk factors associated with nosocomial bloodstream infections caused by multiple clones of the staphylococcal cassette chromosome mec (SCCmec) type IV strain of methicillin-resistant Staphylococcus aureus (MRSA).

DESIGN

An unmatched case-control study (at a ratio of 1:2) performed during the period from October 2002 through September 2003.

SETTING

A 2,000-bed tertiary care teaching hospital affiliated with the University of São Paulo in São Paulo, Brazil.

METHODS

Case patients (n=30) were defined either as patients who had a bloodstream infection due to SCCmec type IV MRSA diagnosed at least 48 hours after hospital admission or as neonates with the infection who were born in the hospital. Control patients (n=60) were defined as patients with SCCmec type III MRSA infection diagnosed at least 48 hours after hospital admission. Genes encoding virulence factors were studied in the isolates recovered from case patients, and molecular typing of the SCCmec type IV MRSA isolates was also done by pulsed-field gel electrophoresis and multilocus sequence typing.

RESULTS

In multivariate analysis, the following 3 variables were significantly associated with having a nosocomial bloodstream infection caused by SCCmec type IV strains of MRSA: an age of less than 1 year, less frequent use of a central venous catheter (odds ratio [OR], 0.07 [95% confidence interval {CI}, 0.02-0.28]; p= .025), and female sex. A second analysis was performed that excluded the case and control patients from the neonatal unit, and, in multivariate analysis, the following variables were significantly associated with having a nosocomial bloodstream infection caused by SCCmec type IV strains of MRSA: less frequent use of a central venous catheter (OR, 0.12 [95% CI, 0.03-0.55]; p= .007), lower Acute Physiology and Chronic Health Evaluation II score on admission (OR, 0.14 [95% CI, 0.03-0.61]; p= .009), less frequent surgery (OR, 0.21 [95% CI, 0.06-0.83]; p= .025), and female sex (OR, 5.70 [95% CI, 1.32-24.66]; p= .020). Of the 29 SCCmec type IV MRSA isolates recovered from case patients, none contained the Panton-Valentine leukocidin, gamma-hemolysin, enterotoxin B or C, or toxic shock syndrome toxin-1. All of the isolates contained genes for the LukE-LukD leukocidin and alpha-hemolysin. Genes for enterotoxin A were present in 1 isolate, and genes for beta-hemolysin were present in 3 isolates.

CONCLUSIONS

"Classical" risk factors do not apply to patients infected with the SCCmec type IV strain of MRSA, which is an important cause of nosocomial bacteremia. This strain infects a patient population that is less ill and has had less frequent invasive procedures than a patient population infected with the multidrug-resistant strain of SCCmec type III MRSA. We found that virulence factors were rare and that Panton-Valentine leukocidin was absent. There were multiple clones of the SCCmec type IV strain in our hospital. Children under 1 year of age were at a higher risk. There was a predominant clone (sequence type 5) in this patient population.

Emergence of and risk factors for methicillin-resistant Staphylococcus aureus of community origin in intensive care nurseries

OBJECTIVE

The goal of this study was to define more clearly the impact of community-acquired methicillin-resistant Staphylococcus aureus clones (eg, USA300 and USA400) on colonization and infection in infants in intensive care nurseries and potential modes of transmission of community-acquired methicillin-resistant S aureus clones.

METHODS

Prospective surveillance for methicillin-resistant S aureus colonization and infection was performed among infants in the intensive care nurseries at Grady Memorial Hospital (Atlanta, GA) between 1993 and 2006. Beginning in September 2004, nares surveillance cultures were collected at admission. Methicillin-resistant S aureus isolates were genotyped by using pulsed-field gel electrophoresis and multiplex polymerase chain reaction assays for staphylococcal chromosomal cassette mec gene complex type and Panton-Valentine leukocidin genes. Prevalence of and risk factors for colonization with community-acquired versus health care-associated methicillin-resistant S aureus clones (eg, USA100) were assessed.

RESULTS

Between 1993 and 2006, 130 (3.5%) of 3707 infants were identified to be colonized with methicillin-resistant S aureus. Twelve (1.2%) of 996 admission nares cultures were positive for methicillin-resistant S aureus (since initiation of admission cultures in September 2004). Community-acquired methicillin-resistant S aureus clones were first recovered in 1998; the proportion of methicillin-resistant S aureus clones of community origin increased significantly between 1998 and 2004. Multivariate analysis identified vaginal delivery and maternal smoking, both among infants of mothers receiving systemic antibiotic treatment before delivery, as independent predictors for neonatal colonization with community-acquired methicillin-resistant S aureus. Systemic antibiotic therapy before delivery for nonsmoking mothers delivering through cesarean section and possibly endotracheal intubation were associated with the recovery of health care-associated methicillin-resistant S aureus clones.

CONCLUSIONS

Community-acquired methicillin-resistant S aureus clones have emerged as a major cause of methicillin-resistant S aureus colonization in high-risk newborns. Community-acquired methicillin-resistant S aureus recovery was associated with acquisition during birth, whereas health care-associated methicillin-resistant S aureus clones seemed to be transmitted nosocomially.

The emergence of community-associated methicillin-resistant Staphylococcus aureus at a London teaching hospital, 2000-2006

We used ciprofloxacin susceptibility as a phenotypic marker of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in a London hospital collection of MRSA isolates from inpatients, outpatients and primary-care clinics during 2000-2006. Four-hundred and fifty-eight ciprofloxacin-susceptible (Cip-S) MRSA isolates were reported; antimicrobial susceptibility, staphylococcal cassette chromosome mec (SCCmec) type, spa type and the presence of Panton-Valentine leukocidin (PVL) genes were determined for all 194 surviving Cip-S MRSA isolates. Multilocus sequence typing and pulsed-field gel electrophoresis were performed on representative isolates. Clinical and epidemiological features of Cip-S MRSA infections were consistent with CA-MRSA, the incidence of which increased markedly during the study period from 49 in 2000 to 102 in 2006. Most (82.0%) of the surviving Cip-S MRSA isolates were SCCmec IV and 25.3% were PVL-positive. Considerable clonal heterogeneity was noted among the recovered isolates, including the t044/ST80-IV European clone and the PVL-negative t127/ST1-IV clone; PVL-positive t008/ST8-IV (USA300) isolates were rare. Ciprofloxacin susceptibility is a useful screening marker of CA-MRSA strains in London, which are more frequent than previously thought and whose incidence is increasing.