Community-associated strains of methicillin-resistant Staphylococccus aureus as the cause of healthcare-associated infection.

OBJECTIVE: Methicillin-resistant Staphylococcus aureus (MRSA) isolates from patients with community-associated infection have been described as strains genetically distinct from the strains isolated from patients with healthcare-associated infection. This study examines the hypothesis that community-associated MRSA (CA-MRSA) strains now cause serious infections in hospitalized patients. METHODS: Thirty-seven clinical MRSA isolates were randomly selected from blood isolates obtained from July 2003 through June 2004. Strains were tested for staphylococcal chromosomal cassette mec (SCCmec) type, pulsed-field gel electrophoresis (PFGE) type, and presence of Panton-Valentine leukocidin (PVL) genes. Medical records review and epidemiologic classification was performed by an investigator blinded to the results of the bacterial strain analysis. Episodes of bloodstream infection were independently classified as either community-associated or healthcare-associated infections, and bacterial isolates were independently classified as either CA-MRSA strains or healthcare-associated MRSA (HA-MRSA) strains, according to established definitions. SETTING: A tertiary care Veterans Affairs Medical Center. RESULTS: Twenty-four (65%) of 37 MRSA isolates were SCCmec type IV, a genetic type characteristic of CA-MRSA strains; 22 of these 24 isolates belonged to the CA-MRSA clone USA300 and carried PVL genes. Thirteen (35%) of the 37 strains were SCCmec type II, of which 12 were USA100-ST5 and 12 lacked PVL genes. Thirty patients (81%) had healthcare-associated infections; 18 (60%) of these 30 were infected with isolates carrying markers of CA-MRSA strains. Of 7 patients with CA-MRSA infections, 6 were infected with isolates belonging to the USA300 clone. Patients with healthcare-associated bloodstream infections were as likely to be infected with a CA-MRSA strain as patients with a community-associated infection (P = .38). CONCLUSIONS: MRSA strains with molecular characteristics of CA-MRSA strains have emerged as an important cause of serious healthcare-associated infection in our hospital.     

Methicillin-resistant Staphylococcus aureus clones, Western Australia

Community-associated methicillin-resistant Staphylococcus aureus (MRSA) was first reported in Western Australia in the early 1990s from indigenous peoples living in remote areas. Although a statewide policy of screening all hospital patients and staff who have lived outside the state for MRSA has prevented the establishment of multidrug-resistant epidemic MRSA, the policy has not prevented SCCmec type IV and type V MRSA clones from becoming established. Of the 4,099 MRSA isolates analyzed (referred to the Gram-positive Bacteria Typing and Research Unit) from July 2003 to December 2004, 77.5% were community-associated MRSA (CA-MRSA). Using multilocus sequence/staphylococcal chromosome cassette mec typing, 22 CA-MRSA clones were characterized. Of these isolates, 55.5% were resistant to >1 non-beta-lactam antimicrobial drug. Five Panton-Valentine leukocidin (PVL)-positive CA-MRSA clones were identified. The emergence of multidrug-resistant CA-MRSA clones and the detection of PVL toxin genes in clones previously reported as PVL negative is a major public health concern.     

Molecular epidemiology of methicillin-resistant Staphylococcus aureus, rural southwestern Alaska

USA300 is the dominant strain responsible for community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) infections in most of the United States. We examined isolates from outbreaks of MRSA skin infections in rural southwestern Alaska in 1996 and 2000 (retrospective collection) and from the hospital serving this region in 2004-2006 (prospective collection). Among 36 retrospective collection isolates, 92% carried Panton-Valentine leukocidin (PVL) genes; all carried staphylococcal chromosomal cassette mec (SCCmec) type IV. None belonged to clonal complex (CC) 8, the CC associated with USA300; 57% were sequence type (ST) 1, and 26% were ST30; 61% were clindamycin resistant. In the prospective collection, 42 isolates were PVL+ and carried SCCmec type IV; 83.3% were ST1, 9.5% were ST30, and 7.1% were ST8. Among 120 prospective isolates, 57.5% were clindamycin resistant. CA-MRSA epidemiology in southwestern Alaska differs from that in the lower 48 states; ST8 strains were rarely identified and clindamycin resistance was common.     

Genetic diversity of community-associated methicillin-resistant Staphylococcus aureus isolated from Tenerife Island, Spain

With the recent detection of MRSA (methicillin-resistant Staphylococcus aureus) infections in patients lacking health care-related risk factors, the term community-acquired MRSA (CA-MRSA) has been become widely recognised. Many cases of CA-MRSA spreading to the community have been described worldwide. The aim of this study was to determine the features of CA-MRSA isolates from Tenerife Island. Toward this end, one hundred MRSA isolates were collected from eight different health regions, and their molecular features were investigated. This study revealed a wide variety of MRSA clones, including an emergent ST: ST1434 (CC8) and two new spa types, t7575 (ST125) and t7678 (ST22). The PVL genes were found in only five isolates belonging to unrelated lineages, ST8, ST30 and ST22, which could indicate at least three independent introductions of PVL(+) strains to Tenerife. Moreover, we detected that hospital MRSA clones, like EMRSA-15 and EMRSA-16, had spread to the community and are now circulating in both environments. Therefore, in our study, the CDC's rules were not specific enough to distinguish CA-MRSA from HA-MRSA. Thus, we think that the current epidemiological information is not enough to discriminate between both MRSAs, and it is necessary for prevention guidelines to include the routine determination of at least the genetic background, the antimicrobial susceptibility profile, and the PVL genes of each MRSA isolate.     

MRSA in children presenting to hospitals in Birmingham, UK

Meticillin-resistant Staphylococcus aureus (MRSA) isolates from children presenting to Birmingham hospitals were characterized using molecular methods. The study was performed on MRSA isolates from children aged 相似文献   

Virulence factors produced by strains of Staphylococcus aureus isolated from urinary tract infections

Staphylococcus aureus infections are widely prevalent in West Africa and are often associated with urinary tract infections (UTIs). Virulence factors from S. aureus have rarely been described for such infections. The purpose of the current study was to determine the prevalence of toxins and adhesion factors obtained from S. aureus isolated from presumed primary UTIs at the Cotonou University Hospital (CUH) in Benin as compared with the Strasbourg University Hospital (SUH) in France. Both ambulatory and hospitalised patients were included in the study. Sixty-five independent strains of S. aureus from CUH and 35 strains from SUH were obtained over a four-month period. Virulence factors were characterised by immunodetection or multiplex polymerase chain reaction, and meticillin susceptibility was recorded. Approximately 50% of all isolates produced at least one enterotoxin. No isolate from SUH produced Panton-Valentine leucocidin (PVL), whereas 21.5% of the S. aureus isolates from CUH produced PVL (P<0.01). Six of 14 (43%) PVL-positive isolates were meticillin-resistant. At SUH, the incidence of MRSA (57%) was significantly higher (P<0.01) than at CUH (14%). Genes encoding clumping factor B, and elastin and laminin binding proteins were detected in almost all isolates (80%), irrespective of the geographical origin. The results for elastin binding protein differed significantly from published data regarding isolates from other clinical origins. Staphylococcal toxins and adhesion factors may be important in the physiopathology of UTI.     

Virulence determinants in community and hospital meticillin-resistant Staphylococcus aureus

Staphylococcus aureus produces many virulence factors, most of which act in a synergistic and coordinated fashion. Some appear to be specifically associated with certain severe infections and are produced by meticillin-resistant Staphylococcus aureus (MRSA) clones distributed worldwide. Superantigenic exotoxins appear to be major virulence factors in hospital MRSA clones (HA-MRSA), and staphylococcal enterotoxin A (SEA) may be involved in the physiopathology of septic shock. Panton Valentine Leucocidin (PVL) has emerged as a major virulence factor in community-acquired Staphylococcus aureus (CA-MRSA) infections. In particular, the leukotoxic action of PVL is responsible for the high mortality rate associated with necrotizing pneumonia. CA-MRSA can also harbour the toxic shock toxin 1 (TSST-1) and rarely the exfoliative toxin.     

Emergence of USA300 MRSA in a tertiary medical centre: implications for epidemiological studies

Community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) has become a major pathogen, particularly in outbreaks of skin and soft-tissue infection (SSTI). A preliminary study conducted at our institution in 2004 revealed that up to 45% of inpatient and 70% of outpatient MRSA isolates tested were the USA300 genotype. In this report, we used pulsed-field gel electrophoresis (PFGE) in a retrospective analysis to determine the time when CA-MRSA USA300 moved from the community to the inpatient population. During the five-year period 2000 to 2004, unique MRSA isolates (N=253) were selected from inpatients in surgical and medical intensive care units, the general hospital population and outpatients. The most common PFGE types found in all populations from 2000 to 2003 were USA100, USA200 and USA600. USA300 was absent from all inpatients from 2000 to 2003 and only sporadic numbers found in the outpatient group. However, in 2004 the USA300 strain emerged in both outpatient and hospitalised patients. There was no difference in the distribution of USA300 between ICUs and the general inpatient population. The emergence of CA-MRSA has resulted in a shift of the MRSA strains that are implicated in healthcare-associated infections in our institution. This has been a recent development that has implications as to the use of PFGE to determine transmission of MRSA in the inpatient setting. Further evaluation of these data in the context of the epidemiology of these infections is needed to determine if more discriminatory approaches to typing will be required for monitoring the spread of the more virulent CA-MRSA phenotype within the inpatient population.     

Community-associated methicillin-resistant Staphylococcus aureus in pediatric patients

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections increased from 2000 to 2003 in hospitalized pediatric patients in Houston. CA-MRSA was associated with greater illness than was infection with methicillin-susceptible strains. Children with CA-MRSA were younger and mostly African American. Of MRSA isolates, 4.5% had the inducible macrolide-lincosamide-streptogramin B phenotype.     

Control of a cluster of community-associated, methicillin-resistant Staphylococcus aureus in neonatology

To control an outbreak of community-associated MRSA (CA-MRSA) in a neonatology unit, an investigation was conducted that involved screening neonates and parents, molecular analysis of MRSA isolates and long-term follow-up of cases. During a two-month period in the summer of 2000, Panton-Valentine leukocidin (PVL)-producing CA-MRSA (strain ST5-MRSA-IV) was detected in five neonates. The mother of the index caseshowed signs of mastitis and wound infection and consequently tested positive for CA-MRSA. A small cluster of endemic, PVL-negative MRSA strains (ST228-MRSA-I) occurred in parallel. Enhanced hygiene measures, barrier precautions, topical decolonization of carriers, and cohorting of new admissions terminated the outbreak. Four months after the outbreak, the mother of another neonate developed furunculosis with the epidemic CA-MRSA strain. One infant had persistent CA-MRSA carriage resulting in skin infection in a sibling four years after the outbreak. In conclusion, an epidemic CA-MRSA strain was introduced by the mother of the index case. This spread among neonates and was subsequently transmitted to another mother and a sibling. This is the first report of a successfully controlled neonatology outbreak of genetically distinct PVL-producing CA-MRSA in Europe.     

Community-associated methicillin-resistant Staphylococcus aureus isolates causing healthcare-associated infections

We noted a marked increase in healthcare-associated (HA) methicillin-resistant Staphylococcus aureus (MRSA) infections caused by isolates phenotypically consistent with community-associated (CA)-MRSA strains. To study this trend, we retrospectively examined all HA-MRSA isolates from patients in our institution during 1999-2004. An isolate was considered an SCCmecIV phenotype if it had antimicrobial drug susceptibilities consistent with typical CA-MRSA isolates. Our phenotypic definition was validated in a limited subset of isolates by SCCmec genotype, pulsed-field gel electrophoresis, and multilocus sequence typing. Among 352 patients with HA-MRSA isolates, SCCmecIV phenotype increased from 17% in 1999 to 56% in 2003 (p < 0.0001). Antimicrobial drug-susceptibility phenotype and genotype were consistent in 21 (91%) of 23 isolates. In a multivariate model, the SCCmec type IV phenotype was independently associated with wound culture source, later year of collection, and MRSA isolated earlier during hospitalization. In conclusion, MRSA isolates phenotypically similar to CA strains have become the predominant isolates associated with HA-MRSA in our hospital.     

Community strains of methicillin-resistant Staphylococcus aureus as potential cause of healthcare-associated infections, Uruguay, 2002-2004

Community-associated MRSA (CA-MRSA) strains have emerged in Uruguay. We reviewed Staphylococcus aureus isolates from a large healthcare facility in Montevideo (center A) and obtained information from 3 additional hospitals on patients infected with CA-MRSA. An infection was defined as healthcare-onset if the culture was obtained >48 hours after hospital admission. At center A, the proportion of S. aureus infections caused by CA-MRSA increased from 4% to 23% over 2 years; the proportion caused by healthcare-associated MRSA (HA-MRSA) decreased from 25% to 5%. Of 182 patients infected with CA-MRSA, 38 (21%) had healthcare-onset infections. Pulsed-field gel electrophoresis determined that 22 (92%) of 24 isolates were USA1100, a community strain. CA-MRSA has emerged in Uruguay and appears to have replaced HA-MRSA strains at 1 healthcare facility. In addition, CA-MRSA appears to cause healthcare-onset infections, a finding that emphasizes the need for infection control measures to prevent transmission within healthcare settings.     

Clinical and laboratory features of community-associated methicillin-resistant Staphylococcus aureus: is it really new?

OBJECTIVE: To review the epidemiologic and molecular characteristics of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) in Detroit, Michigan, to assess the risk factors for infection and the response to therapy. DESIGN: Prospective clinical and laboratory study of 2003-2004 CA-MRSA isolates. Molecular features were compared with CA-MRSA isolates from 1980. SETTING: A 600-bed urban academic medical center. PATIENTS: Twenty-three patients with CA-MRSA infections from 2003-2004 were evaluated. In addition, laboratory analysis was performed on 13 CA-MRSA isolates from 1980. MAIN OUTCOME MEASURES: Laboratory analysis of isolates included antimicrobial susceptibility testing, pulsed-field genotyping, testing for Panton-Valentine leukocidin (PVL) genes, and staphylococcal cassette chromosome mec typing. RESULTS: Patients were predominantly young African American males and presented with skin and soft-tissue infections. All isolates were resistant to erythromycin and highly susceptible to other agents. Patients were generally treated successfully with combination incision and drainage and systemic antibiotics. Among the 23 isolates, 20 (87%) were the same strain. This strain carried the staphylococcal cassette chromosome mec type IV and PVL genes and is genetically identical to USA 300. Thirteen isolates of patients from our community who presented with CA-MRSA infections in 1980 represented a single clone that is unique compared with the 2003-2004 isolates. This strain carried staphylococcal cassette chromosome mec type IVA but did not carry the PVL genes. CONCLUSIONS: In our community, CA-MRSA is largely due to a single clone with a type IV mec gene and PVL gene. The type IV staphylococcal cassette chromosome mec type can be demonstrated in CA-MRSA isolates from a remote period, suggesting that earlier outbreaks were not related to healthcare exposure.     

Management of a large healthcare-associated outbreak of Panton-Valentine leucocidin-positive meticillin-resistant Staphylococcus aureus in Germany

We report the largest documented healthcare-associated outbreak of Panton-Valentine leucocidin-positive meticillin-resistant Staphylococcus aureus (PVL(+) MRSA) in Europe. Six index patients from three long-term care facilities (LTCFs) were screened positive for PVL(+) MRSA in 2004 on admission to a community hospital in Germany. The purpose of this prospective study was to describe the prevalence of PVL(+) MRSA in the LTCFs before and after infection control interventions. Screening for MRSA with or without PVL was performed in all three LTCFs in 2004 [453 residents, 240 healthcare workers (HCWs)] and 2005 (440 residents, 192 HCWs). Swabs from anterior nares and wounds, if applicable, were collected. Colonised residents and staff were treated with mupirocin nasal ointment and topical antiseptics, and staff were provided with hygiene education. Total MRSA carrier rate of residents and HCWs in 2004 was 11.3% (PVL(+) MRSA 9.1%, PVL(-) MRSA 2.2%). There were comparable carrier rates between residents and HCWs in each LTCF. All PVL(+) MRSA isolates were of clonal origin (MLST 22) representing a novel spa sequence type t310. A decrease in total MRSA prevalence (from 11.3 to 5.5%) and PVL(+) MRSA (from 9.1 to 3.3%) was observed in 2005. The rate of PVL(-) MRSA remained unaffected. No symptomatic skin infections were noted among residents or HCWs. In this outbreak incomplete control of PVL(+) MRSA presumably resulted from difficult and delayed detection and decolonisation of carriers, incomplete compliance with control measures and lack of enforcement by public health authorities.     

Community-associated methicillin-resistant Staphylococcus aureus in hospital nursery and maternity units

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has rarely been reported in the hospital setting. We report an outbreak of 7 cases of skin and soft tissue infections due to a strain of CA-MRSA. All patients were admitted to the labor and delivery, nursery, or maternity units during a 3-week period. Genetic fingerprinting showed that the outbreak strain was closely related to the USA 400 strain that includes the midwestern strain MW2. All isolates contained the staphylococcal chromosome cassette mec type IV. Genes for Panton-Valentine leukocidin and staphylococcal enterotoxin K were detected in all isolates, and most contained other enterotoxin genes. Testing of nearly 2,000 MRSA isolates collected during citywide surveillance studies from 1999 to 2003 showed that approximate, equals 1% were genetically related to MW2. CA-MRSA strain MW2 has been present in this region at least since 1999. This study documents the spread of this strain among healthy newborns at 1 hospital.     

耐甲氧西林金黄色葡萄球菌SCCmec基因分型及PVL基因研究

目的了解耐甲氧西林金黄色葡萄球菌(MRSA)SCCmec基因型的分布特征并检测杀白细胞毒素(PVL)基因。方法收集2007年10月-2008年5月临床标本中,分离的非重复金黄色葡萄球菌110株,用头孢西丁纸片扩散法对MRSA进行初筛;用多重聚合酶链反应(PCR)对MRSA进行SCCmec基因分型及PVL基因检测;用琼脂稀释法对MRSA菌株进行抗菌药物最低抑菌浓度(MIC)检测。结果 64株MRSA中,63株医院获得性(HA)-MRSA,1株社区获得性(CA)-MRSA,其中SCCmecⅢ型57株(89.0%),Ⅱ型1株(1.6%),SCCmecⅣ型1株(1.6%),未分型5株(7.8%);未发现SCCmecⅠ、Ⅴ型菌株;SCCm ecⅡ型、SCCm ecⅢ型的菌株均为多药耐药株,SCCmecⅣ型的菌株除对β-内酰胺类抗菌药物耐药外,对其他类抗菌药物较敏感。结论 HA-MRSA主要以SCCmecⅢ型为主,CA-MRSA菌株为SCCmecⅣ型,携带PVL毒力基因,HA-MRSA对抗菌药物呈多药耐药性,CA-MRSA菌株耐药谱比HA-MRSA菌株耐药谱窄,加强对MRSA的监测,对指导临床合理使用抗菌药物具有重要意义。     

Meticillin-resistant Staphylococcus aureus: occurrence of a new spa type in two acute care hospitals in Austria

Typing multiply-resistant bacteria using molecular techniques is high priority for national health authorities. Routine typing of meticillin-resistant Staphylococcus aureus (MRSA) was initiated in Austria 2005 and was performed by sequence analysis of the variable X region of protein A gene (spa), characterisation of the mec gene (SCCmec) and testing for Panton-Valentine leukocidin (PVL), enterotoxins, toxic shock syndrome toxin and the epidermolytic toxin genes. Ten different spa types, including newly identified t2023, were found among 66 clinical MRSA isolates originating from two neighbouring hospitals under the same management. Spa type t2023 was initially isolated in December 2005 from hospital A, where it became the dominant spa type during 2006 (nine of 16 isolates). The occurrence of type t2023 in hospital B remained a unique event and could be epidemiologically linked to a patient transferred from hospital A. Spa type t2023 is very similar to spa type t001. An isolate of spa type t001 from hospital A showed an enterotoxin gene pattern, multilocus sequence type (MLST) and SmaI macrorestriction PFGE pattern indistinguishable from that of t2023. Epidemiological differences suggested that infection control measures can prevent MRSA cross-transmission. Hospital B had a more stringent MRSA isolation policy, a higher nurse:patient ratio and provided more resources for infection control than hospital A.     

Community-acquired methicillin-resistant Staphylococcus aureus carrying Panton-Valentine leukocidin genes: worldwide emergence

Infections caused by community-acquired (CA)-methicillin--resistant Staphylococcus aureus (MRSA) have been reported worldwide. We assessed whether any common genetic markers existed among 117 CA-MRSA isolates from the United States, France, Switzerland, Australia, New Zealand, and Western Samoa by performing polymerase chain reaction for 24 virulence factors and the methicillin-resistance determinant. The genetic background of the strain was analyzed by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). The CA-MRSA strains shared a type IV SCCmec cassette and the Panton-Valentine leukocidin locus, whereas the distribution of the other toxin genes was quite specific to the strains from each continent. PFGE and MLST analysis indicated distinct genetic backgrounds associated with each geographic origin, although predominantly restricted to the agr3 background. Within each continent, the genetic background of CA-MRSA strains did not correspond to that of the hospital-acquired MRSA.     

Community-acquired methicillin-resistant Staphylococcus aureus infection in Singapore is usually "healthcare associated".

OBJECTIVE: To assess the frequency of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections. SETTING: A teaching hospital in Singapore. METHODS: Prospectively collected surveillance data were reviewed during a 1-year period to determine the extent and origin of community-acquired MRSA infections. RESULTS: Whereas 32% of 383 MRSA infections were detected less than 48 hours after hospital admission and would, by convention, be classified as "community acquired," all but one of these were among patients who had been exposed to outpatient centers including dialysis or chemotherapy clinics, visiting nurses, community hospitals, or all three. CONCLUSIONS: With health care increasingly being delivered in an outpatient setting, community-acquired MRSA infections are often acquired in hospital-related sites and most may be more accurately described as "healthcare acquired." Infection control measures need to move beyond the traditional paradigm of acute care hospitals to effectively control the spread of resistant pathogens.     

Community-associated Methicillin-Resistant Staphylococcus aureus Strains in Pediatric Intensive Care Unit

Virulent community-associated methicillin-resistant Staphylococcus-aureus (CA-MRSA) strains have spread rapidly in the United States. To characterize the degree to which CA-MRSA strains are imported into and transmitted in pediatric intensive care units (PICU), we performed a retrospective study of children admitted to The Johns Hopkins Hospital PICU, March 1, 2007–May 31, 2008. We found that 72 (6%) of 1,674 PICU patients were colonized with MRSA. MRSA-colonized patients were more likely to be younger (median age 3 years vs. 5 years; p = 0.02) and African American (p<0.001) and to have been hospitalized within 12 months (p<0.001) than were noncolonized patients. MRSA isolates from 66 (92%) colonized patients were fingerprinted; 40 (61%) were genotypically CA-MRSA strains. CA-MRSA strains were isolated from 50% of patients who became colonized with MRSA and caused the only hospital-acquired MRSA catheter-associated bloodstream infection in the cohort. Epidemic CA-MRSA strains are becoming endemic to PICUs, can be transmitted to hospitalized children, and can cause invasive hospital-acquired infections. Further appraisal of MRSA control is needed.