Use of molecular epidemiology to monitor the nosocomial dissemination of methicillin-resistant Staphylococcus aureus in a University Hospital from 1991 to 2001

The History of Methicillin-Resistant Staphylococcus aureus in Brazil

Since the emergence of MRSA in the 1960s, a gradual increase in infections by resistant bacteria has been observed. Clinical manifestations may vary from brand to critical condition due to host risk factors, as well as pathogen virulence and resistance. The high adaptability and pathogenic profile of MRSA clones contributed to its spread in hospital and community settings. In Brazil, the first MRSA isolates were reported in the late 1980s, and since then different genetic profiles, such as the Brazilian epidemic clone (BEC) and other clones considered a pandemic, became endemic in the Brazilian population. Additionally, Brazil's MRSA clones were shown to be able to transfer genes involved in multidrug resistance and enhanced pathogenic properties. These events contributed to the rise of highly resistant and pathogenic MRSA. In this review, we present the main events which compose the history of MRSA in Brazil, including numbers and locations of isolation, as well as types of staphylococcal cassette chromosome mec (SCCmec) found in the Brazilian territory.

Universal methicillin-resistant Staphylococcus aureus (MRSA) surveillance for adults at hospital admission: an economic model and analysis

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) transmission and infections are a continuing problem in hospitals. Although some have recommended universal surveillance for MRSA at hospital admission to identify and to isolate MRSA-colonized patients, there is a need for formal economic studies to determine the cost-effectiveness of such a strategy.

METHODS

We developed a stochastic computer simulation model to determine the potential economic impact of performing MRSA surveillance (ie, single culture of an anterior nares specimen) for all hospital admissions at different MRSA prevalences and basic reproductive rate thresholds from the societal and third party-payor perspectives. Patients with positive surveillance culture results were placed under isolation precautions to prevent transmission by way of respiratory droplets. MRSA-colonized patients who were not isolated could transmit MRSA to other hospital patients.

RESULTS

The performance of universal MRSA surveillance was cost-effective (defined as an incremental cost-effectiveness ratio of less than $50,000 per quality-adjusted life-year) when the basic reproductive rate was 0.25 or greater and the prevalence was 1% or greater. In fact, surveillance was the dominant strategy when the basic reproductive rate was 1.5 or greater and the prevalence was 15% or greater, the basic reproductive rate was 2.0 or greater and the prevalence was 10% or greater, and the basic reproductive rate was 2.5 or greater and the prevalence was 5% or greater.

CONCLUSIONS

Universal MRSA surveillance of adults at hospital admission appears to be cost-effective at a wide range of prevalence and basic reproductive rate values. Individual hospitals and healthcare systems could compare their prevailing conditions (eg, the prevalence of MRSA colonization and MRSA transmission dynamics) with the benchmarks in our model to help determine their optimal local strategies.

The potential economic value of a Staphylococcus aureus vaccine for neonates

The continuing morbidity and mortality associated with Staphylococcus aureus (S. aureus) infections, especially methicillin-resistant S. aureus (MRSA) infections, have motivated calls to make S. aureus vaccine development a research priority. We developed a decision analytic computer simulation model to determine the potential economic impact of a S. aureus vaccine for neonates. Our results suggest that a S. aureus vaccine for the neonatal population would be strongly cost-effective (and in many situations dominant) over a wide range of vaccine efficacies (down to 10%) for vaccine costs (or=1%).

Evolution of methicillin-resistant Staphylococcus aureus clones in Latin America

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is a prominent nosocomial bacterial pathogen, associated with significant morbidity and mortality. The global incidence is increasing, and Latin America is no exception. This article reviews MRSA clonal distribution in Latin America and implications for clinical practice.

DESIGN

A PubMed literature search (1966-2008) identified 32 articles that characterized MRSA clones in Latin America.

RESULTS

Data from these articles show that since 1990, several epidemic MRSA clones have spread in Latin America. The multidrug-resistant Brazilian clone is widespread, especially in Brazil and Argentina, but more recently clones with susceptibility to a range of antibiotics have been detected in Brazil, whereas in Argentina, as in Chile, Colombia and Paraguay, the multidrug-resistant Cordobes/Chilean clone prevails. In Mexico, the New York/Japan clone is most frequent. Data were not available from every country and, despite the increasing prevalence of community MRSA infections, most were collected from tertiary care centers.

CONCLUSIONS

A variety of epidemic MRSA clones are circulating in Latin America, some of which harbor genes that encode multidrug resistance or enhanced pathogenicity. Continued collection and reporting of epidemiological data is crucial for effective prevention and treatment.

Genetic similarity between staphylococcus sp isolated from human and hospital settings, and susceptibility to different antimicrobials

One hundred and forty-three samples from human hands and hospital beds were collected at a teaching hospital in the city of Ribeirão Preto/SP by swabs, and placed in BHI broth. Following a 24 h incubation period at 37°C, they were seeded on Petri dishes containing Agar “Staphylococcus Medium 110”. Colonies typical of the genus Staphylococcus were collected and stored at 4°C until tested for catalase, mannitol, hemolysis, DNAse and coagulase. Strains were analyzed by RAPD-PCR to verify their similarity, and tested for sensitivity to ten different antibiotics. From the ninety-two isolated strains, 67 (72,8%) were coagulase- negative and 25 (27,2%) coagulase-positive. Similarity analysis showed a great heterogeneity among strains, but some presented 100% similarity. Resistance to oxacilin was encountered in 39 (42%) of the strains. Two coagulase-negative strains were resistant to vancomycin, and eleven (12%) were considered multiresistant. Measures such as hand disinfection of the staff and hospital beds and rationalization of antibiotic use could contribute to decrease pathogen transmission and selection pressure, diminishing the frequency and lethality of nosocomial infections.

Longitudinal study of the molecular epidemiology of methicillin-resistant Staphylococcus aureus at a university hospital

Surveillance for methicillin-resistant Staphylococcus aureus (MRSA) at the University Hospital of Heidelberg revealed an increase in the numbers of newly detected MRSA isolates in recent years. We conducted a study to assess the dynamics of the changes in the MRSA population. Pulsed-field gel electrophoresis (PFGE) typing of MRSA isolates from all patients at the University Hospital of Heidelberg collected between 1993 and 2004 was performed. The microbiology database contained 1,807 entries for newly detected MRSA isolates from 1,301 patients. A total of 1,252 isolates were available for PFGE typing. The isolates could be classified into 109 different PFGE types. Most PFGE types (n=70) were detected less than five times and showed no evidence of transmission (sporadic strains). They accounted for 8.7% of all isolates, with few variations in frequency over the time. Thirty-seven PFGE types were clustered by time of detection, and transmission of the strains was likely (local epidemic strains). A total of 37.3% of the isolates belonged to this group of strains. The remaining 54.0% of the isolates belonged to only two further PFGE types (endemic strains). One endemic strain accounted for 5.0% of all isolates in 1994 and 68.2% in 2004. A second endemic strain was detected in 1.1% of all isolates in 1998 but in 12.4% in 2004. Statistical analysis of the associations between the kind of strain (sporadic, local epidemic, or endemic) and the patients' characteristics revealed a significant association for age and mode of acquisition. The remarkable increase in the rate of MRSA detection at the University Hospital of Heidelberg is mainly due to the dissemination of two different strains. Infection control measures seemed sufficient to prevent further transmission of some but not all of the strains.

Emergence and resurgence of meticillin-resistant Staphylococcus aureus as a public-health threat

Staphylococcus aureus is a gram-positive bacterium that colonises the skin and is present in the anterior nares in about 25-30% of healthy people. Dependent on its intrinsic virulence or the ability of the host to contain its opportunistic behaviour, S aureus can cause a range of diseases in man. The bacterium readily acquires resistance against all classes of antibiotics by one of two distinct mechanisms: mutation of an existing bacterial gene or horizontal transfer of a resistance gene from another bacterium. Several mobile genetic elements carrying exogenous antibiotic resistance genes might mediate resistance acquisition. Of all the resistance traits S aureus has acquired since the introduction of antimicrobial chemotherapy in the 1930s, meticillin resistance is clinically the most important, since a single genetic element confers resistance to the most commonly prescribed class of antimicrobials--the beta-lactam antibiotics, which include penicillins, cephalosporins, and carbapenems.