VISA/VRSA Infections – Epidemiology
Patients in the ICU and other critically ill patients are at high risk for co- colonization with MRSA and VRE and, possibly, VRSA, since both organisms are . The electronic database Pub Med was searched for all the articles on “ Establishment of MRSA and the emergence of vancomycin-resistant S. aureus ( VRSA). People with the following conditions are at higher risk for VISA/VRSA infection: Previous infections with methicillin-resistant Staphylococcus aureus (MRSA).
Independent risk factors included age odds ratio [OR] 1. None of the co-colonized patients would have been identified with clinical cultures alone. Methicillin-resistant Staphylococcus aureus MRSA and vancomycin-resistant enterococci VRE cause nosocomial infections and are associated with increased rates of illness and death 12.
Both organisms are now endemic in many healthcare institutions, particularly in intensive care units ICUs 3. All known vancomycin-resistant S.
In addition, previous studies in this population have been limited by the use of clinical cultures as markers for colonization, which underestimate the true proportion of patients colonized with these resistant organisms 13 — The aim of this study was to estimate the prevalence, risk factors, and clinical outcomes of patients who are co-colonized by VRE and MRSA upon admission to the medical and surgical ICUs of a tertiary-care facility.
The MICU is a bed, private room unit providing care to patients who have acute or potentially life-threatening medical conditions including hematologic and other malignancies. The SICU is a bed, private room unit providing care to adult patients with solid organ transplantation and abdominal, genitourinary, orthopedic, and otolaryngologic surgery.
During the study period, routine surveillance cultures of the anterior nares for MRSA and perirectal area for VRE were obtained from patients within 48 hours of admission to both ICUs for infection control purposes. Patients may have had multiple admissions during the study period, and all eligible admissions were included in this analysis.
Data Collection and Variables All data were abstracted from the UMMC central data repository that contains the patients' electronic medical records. All coexisting conditions were defined by using International Classification of Diseases, 9th Revision and the Charlson Comorbidity Index Enterococci were isolated by plating perirectal swabs on Columbia Modified CNA agar and examined at 24 and 48 hours.
Vancomycin-resistant, nonmotile enterococci were identified as VRE. Statistical Analyses Three risk factor analyses were conducted: Student t, chi-square, Fisher exact, and Wilcoxon rank sum tests were used for descriptive analyses to assess bivariable differences between groups.
If so, this risk factor was included in the final model. Differences in patients' clinical outcomes after assessing colonization status were also assessed. These variables included length of stay after the ICU admission culture, subsequent positive clinical cultures for VRE or MRSA, in-hospital death rate, and readmission to the index hospital or transfer to another healthcare facility. Subsequent positive clinical cultures were limited to sterile sites, and thus only blood, cerebrospinal fluid, or urine cultures were considered.
Of these, 2, patients Independent risk factors identified with logistic regression for the different colonization states co-colonization, VRE only, or MRSA only were markedly different Table 2. None of the co-colonized patients had clinical cultures positive for both organisms. Discussion Increasing VRSA prevalence in the healthcare setting could result in considerable illness and death To our knowledge, we present the first estimates of the prevalence, risk factors, and clinical outcomes of patients with VRE and MRSA co-colonization.
We show that among patients who had admission cultures taken, 4. Thus, none would have been identified as co-colonized without the active surveillance culturing program in place at our institution. As has been suggested by previously reported cases of VRSA, early identification of these patients is recommended to minimize antimicrobial selective pressure and enhance infection control efforts to reduce the potential for patient-to-patient transmission 57.
Considering the potential for colonization, infection, and transmission of VRSA, treating physicians, hospital staff, and infection control personnel at receiving institutions must be adequately prepared to isolate and treat these patients 22 Previous studies of transmission from vancomycin-intermediate S. Previous studies have also shown that carriage of VRE or MRSA may be persistent, which would increase the potential for co-colonized patients to transmit either or both of these organisms to other patients 25 A mathematical model of the transmission dynamics of VRE has suggested that persistent colonization is the most important factor for increasing the endemic prevalence of this organism in the hospital Furthermore, the potential for prolonged co-colonization could increase the likelihood that these patients would experience sufficient selective pressure for emergence of VRSA.
Recent reviews by Reuf, Fridkin, and Cosgrove et al. This has triggered off alarms in the medical community as S.
Methicillin and Vancomycin Resistant S. aureus in Hospitalized Patients
All the articles were cross-referenced to search for any more available reports- yielding articles. This review will focus on the clinical, epidemiological and laboratory aspects of these infections. The expression of methicillin resistance by S. The origin of mec A gene is unknown.
Expression of methicillin resistance in S. The mec A gene is located within a larger region of chromosome known as the staphylococcal cassette chromosome mec SCCmec region kb. Nosocomial isolates have larger SCCmec, owing to the accumulation over time of integrated plasmids or transposons that contribute to the multi-drug resistance. They are predominantly transferred by person-to-person spread of MRSA in the hospital rather than the spread of the resistant determinant from strain to strain.
The spread of MRSA within institutions is therefore largely due to the transmission of resistant organisms from patient to patient, probably on the hands of transiently colonized healthcare workers. However, cefoxitin is a better inducer of the mec A gene, and disk-diffusion test using cefoxitin gives clearer endpoints and is easier to read and thus is the preferred method than oxacillin.
The following tables show the breakpoints for defining methicillin resistance. Community stains of MRSA e. However, intrinsic virulence characteristics of the organisms can result in clinical manifestations similar to or potentially more severe than traditional healthcare-associated MRSA infections among hospitalized patients.
The prevalence of MRSA colonization and infection in the surrounding community may therefore affect the selection of strategies for MRSA control in healthcare settings.
VISA/VRSA in Healthcare Settings | HAI | CDC
Historically, isolates were distinguished by phenotypic methods, including antibiotic susceptibility testing and bacteriophage typing. Both methods have limitations, as genetically unrelated isolates commonly have the same antibiogram, and many S. Initial techniques compared restriction endonuclease patterns of chromosomal or plasmidDNA. The second-generation of genotyping methods included s southern blot hybridization using gene-specific probes, ribotyping, polymerase chain reaction PCR —based approaches, and pulsed-field gel electrophoresis PFGE.
However, they still remain difficult to standardize between laboratories, and the image-based information is difficult to organize for rapid search and retrieval by computer.
In addition, image-based methods do not provide biological criteria to evaluate the relatedness between different strains. Recent advances in DNA-sequencing technology, including rapid, affordable, high-throughput systems, have made it possible for sequencing to be considered as a viable typing method.
Two different strategies have been used to provide genotyping data: In both genes, the in-frame SSR units are degenerative, variable in number and variable in the order in which repeat units are organized. The genetic alterations in SSR regions include both point mutations and intragenic recombination that arise by slipped-strand mispairing during chromosomal replication and that result in a high degree of polymorphism.
Screening for carriage of MRSA is fundamental for nosocomial infection control, both for epidemiological purposes and decisions on barrier isolation. In an effort to reduce nosocomial transmission of MRSA, surveillance cultures have been recommended at the time of hospital admission for patients at high risk of MRSA carriage.
Hence screening of patients at high risk of MRSA carriage is more practical. Studies have identified several risk factors for MRSA carriage at hospital admission, including prior receipt of antibiotic therapy, especially therapy with fluoroquinolones. Decolonization of persons carrying MRSA in their nares has proved possible with several regimens, which include topical mupirocin alone or in combination with orally administered antibiotics e.
It should be noted that recolonization with the same strain, initial colonization with a mupirocin-resistant strain, and emergence of resistance to mupirocin during treatment can occur.
In contrast, HCP who are colonized with MRSA but are asymptomatic and have not been linked epidemiologically to transmission, do not require decolonization.
VISA/VRSA in Healthcare Settings
If active surveillance cultures are used to detect and isolate patients colonized with MRSA or vancomycin resistant Enterococci VRE, and there is no decolonization of these patients, it is logical to assume that contact precautions would be used for the duration of stay in the setting where they were first implemented.
In general, it seems reasonable to discontinue contact precautions when three or more surveillance cultures for MRSA are repeatedly negative over the course of a week or two in a patient who has not received antimicrobial therapy for several weeks. In several reports, cohorting of patients, cohorting of staff, use of designated beds or units and even unit closure were necessary to control transmission. The glycopeptide vancomycin has been regarded as the drug of choice for the treatment of infections due to methicillin-resistant strains.
This has led to confusion in the definitions and clinical significance of vancomycin resistance. These guidelines are followed in US and Canada.
In most of these publications, surveillance was not performed routinely, the sample size was small, the studies were retrospective, or the methods for screening and identifying heterogeneous VISA varied among studies.