[Non reported spa types in our country in Staphylococcus aureus from adult patients of a school hospital, Santa Fe - Argentina]. / Tipos de spa no reportados en nuestro país en Staphylococcus aureus de pacientes adultos de un hospital escuela, Santa Fe, Argentina.

Staphylococcus aureus is a pathogen associated a different kind of infection. Molecular markers are useful tools to study microbial epidemiology. Twenty two methicillin-resistant S. aureus (MRSA) and 23 methicillin-susceptible S. aureus (MSSA) were studied by mecA gene, SCCmec cassette, Panton Valentine leucocidin (PVL) and spa polymorphism. The clinical data patients were analyzed. MSSA was prevalent in samples different from skin and soft tissue (SST) and in hospitalized patients, whereas MRSA in SST. SCCmec type IV was predominant, followed by type I. Low presence of PVL was found. In MRSA 11 different types of spa were detected, t019 was the most frequent and associated with outpatient, 17 types were found in MSSA and t189 was prevalent. spa t002 was present in MSSA and MRSA. We found 11 types of spa not reported in our country.

[MLVA analysis and virulence profile of community-acquired methicillin-resistant Staphylococcus aureus causing infections in Paraguayan children]. / Análisis MLVA y perfil de virulencia de aislamientos de Staphylococcus aureus resistentes a la meticilina adquiridos en la comunidad causantes de infecciones pediátricas en Paraguay.

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is one of the first causes of skin and soft tissue infections, and can also produce severe diseases such as osteomyelitis and pneumonia. The aim of this descriptive study was to determine the SCCmec type and virulence profile and to study the genetic diversity by MLVA analysis of 21 CA-MRSA isolates that infected Paraguayan children in 2010. The SCCmec type and virulence factors were performed by PCR and genetic diversity by MLVA (multiple locus variable analysis). All the isolates carried SCCmec cassette iv. hla, hlb and sea genes were detected in 28,6%, 9,5% and 4,8% respectively. The MLVA analysis showed high genetic diversity with congruent antibiotic resistance and virulence profiles. This study revealed the presence of CA-MRSA harbouring SCCmeciv with high genetic diversity, providing information not available in our country.

[Update on antibiotic resistance in Gram-positive bacteria]. / Actualización en la resistencia antibiótica en Gram positivos.

Antimicrobial resistance among Gram-positive bacteria, especially in Staphylococcus aureus, Enterococcus faecium, Enterococcus faecalis, and Streptococcus pneumoniae, is a serious threat to public health. These microorganisms have multiple resistance mechanisms to agents currently used in clinical practice. Many of these resistance mechanisms are common to all 4 of these bacterial species, but other mechanisms seem to be more specific. The prevalence and dissemination of these mechanisms varies considerably, depending on the microorganism. This review discusses the resistance mechanisms to the most clinically relevant antibiotics, with particular emphasis on the new mechanisms described for widely used antibiotics and for newer agents such as lipopeptides, lipoglycopeptides, glycylcyclines and oxazolidinones.

Vancomycin heteroresistant community associated methicillin-resistant Staphylococcus aureus ST72-SCCmecIVa strain colonizing the nostrils of a five-year-old Spanish girl.

BACKGROUND AND OBJECTIVES: During a community methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization study, an MRSA strain with vancomycin hetero-resistance (h-VISA) was isolated from a five year-old girl with tetralogy of Fallot without previous exposure to vancomycin. An extended nasal colonization study was performed on all her close relatives. RESULTS: Only the patient and her sister were colonized by an h-VISA MRSA strain (clone USA 700, ST72, t148, agr 1 and SCCmec IVa). Mupirocin decolonisation was effective in the elder sister. A new nasal decolonisation in the younger girl using fusidic acid was also successful. However, after decolonisation both sisters were colonized by a methicillin-susceptible S. aureus (ST30, t012 and agr 3) previously isolated from their mother's nostrils. CONCLUSION: As S. aureus have a great capacity to spread among people in close contact, knowledge of a patients' colonization status, tracing contacts, and a correct management are critical issues for the successful containment of multiresistant staphylococci.

Staphylococcus aureus nasal carriage in health care workers: First report from a major public hospital in Argentina.

Staphylococcus aureus causes numerous mild to severe infections in humans, both in health facilities and in the community. Patients and health care workers (HCWs) may disseminate strains during regular medical examinations or hospitalization. The aim of this study was to determine the nasal carriage rate of methicillin-susceptible and methicillin-resistant S. aureus among health care workers at Hospital Provincial del Centenario, a public general hospital in Rosario, Argentina. A transversal study was conducted on 320 health care workers. Nasal swabs were taken and presumptive S. aureus colonies were isolated. Bacterial identity and methicillin resistance status were confirmed by amplification of the nuc and mec genes. Chi square test and Fisher exact test were used for statistical analysis. Of 320 HCWs, 96 (30%) were nasal carriers of S. aureus, 20 of whom (6.3%) carried methicillin-resistant S. aureus (MRSA) and 76 (23.7%) methicillin-susceptible S. aureus (MSSA). Carriage was within thepublished values for physicians (30%) and higher for technicians (57%). Accompanying resistance (62/96, 64.6%) was detected, including resistance to fluoroquinolones (23/96, 24%), aminoglucosides (13/96, 13.5%) or to macrolides (33/96, 34.4%). All the strains were susceptible to vancomycin whereas only 3.1% (3/96), all of them on MSSA strains, were resistant to mupirocin. This study is the first one of its kind in Argentina and one of the few performed in South America, to highlight the relevance of nasal carriage of MRSA and MSSA in health care personnel and brings to light the need for consensus recommendations for regular S. aureus carriage screening as well as for decolonization strategies.

[Spread of genetically related methicillin-susceptible Staphylococcus aureus belonging to CC45, in healthy nasal carriers in Child Day Care Centers of Medellin, Colombia]. / Diseminación de cepas Staphylococcus aureus sensible a meticilina (SASM) relacionadas genéticamente, pertenecientes al CC45, entre portadores nasales sanos de hogares infantiles de Medellín, Colombia.

INTRODUCTION: Colonization plays a major role in the epidemiology and pathogenesis of Staphylococcus aureus infections. The child population is one of the most susceptible to colonization; however, community and children studies are limited in Colombia. OBJECTIVE: To assess the clonal relationship of S.aureus strains isolated from colonized children in eight day care centers (DCCs) from Medellin and to determine the presence of epidemiological characteristics in these populations. METHODS: An observational cross-sectional study was conducted on a sample of 200 children aged from 6 months to 5 years attending eight DCCs in Medellin, Colombia, during 2011. Nasal samples were collected from each nostril. The isolates species and methicillin resistance were molecularly confirmed using nuc and mec genes. Genotypic analysis included SCCmec typing, spa typing, PFGE and MLST. Epidemiological information was obtained from the parents and analyzed using the statistics program SPSS 21.0 RESULTS: The colonization frequency in DCCs ranged from 16.7% (n=3) to 53.6% (n=15). Genetically related isolates were identified inside four DCCs. Half (50%) of the isolates were grouped in 3 clusters, which belonged to the clonal complexes CC45, CC30, and CC121. CONCLUSION: Molecular typing of isolates from colonized children and comparison among DCCs showed the spread of colonizing strains inside DCCs in Medellin; predominantly the CC45 clone, a successful child colonizer.

[Survey of methicillin-resistant Staphylococcus aureus control measures in hospitals participating in the VINCat program]. / Encuesta de las medidas de control de Staphylococcus aureus resistente a meticilina en los hospitales que participan en el programa VINCat.

INTRODUCTION: VINCat is a nosocomial infection surveillance program in hospitals in Catalonia. The aim of the study was to determine the surveillance and control measures of methicillin-resistant Staphylococcus aureus (MRSA) in these centres. METHODS: An e-mail survey was carried out from January to March 2013 with questions related to the characteristics of the hospitals and their control measures for MRSA. RESULTS: A response was received from 53 hospitals (>500 beds: 7; 200-500 beds: 14;<200 beds: 32; had ICU: 29). Computer alert of readmissions was available in 63%. There was active surveillance of patients admitted from another hospital (46.2%) or a long-term-care centre (55.8%), both being significantly more common measures in hospitals with a rate of MRSA≤22% (global median). Compliance with hand hygiene was observed in 77.4% of the centres, and was greater than 50% in 69.7% of them. All hospitals had contact precautions, although 62.3% did not have exclusive frequently used clinical material in bedrooms. The room cleaning was performed more frequently in 54.7% of hospitals, and 67.9% of them had programs for the appropriate use of antibiotics. CONCLUSIONS: This study provides information on the implementation of measures to prevent MRSA in hospitals participating in the VINCat program. Most of the centres have an MRSA protocol, however compliance with it should be improved, especially in areas such as active detection on admission in patients at risk, hand hygiene adherence, cleaning frequency and optimising the use of antibiotics.

Nosocomial pneumonia caused by methicillin-resistant Staphylococcus aureus treated with linezolid or vancomycin: A secondary economic analysis of resource use from a Spanish perspective.

OBJECTIVES: Adopting a unique Spanish perspective, this study aims to assess healthcare resource utilization (HCRU) and the costs of treating nosocomial pneumonia (NP) produced by methicillin-resistant Staphylococcus aureus (MRSA) in hospitalized adults using linezolid or vancomycin. An evaluation is also made of the renal failure rate and related economic outcomes between study groups. DESIGN: An economic post hoc evaluation of a randomized, double-blind, multicenter phase 4 study was carried out. SCOPE: Nosocomial pneumonia due to MRSA in hospitalized adults. PARTICIPANTS: The modified intent to treat (mITT) population comprised 224 linezolid- and 224 vancomycin-treated patients. INTERVENTIONS: Costs and HCRU were evaluated between patients administered either linezolid or vancomycin, and between patients who developed renal failure and those who did not. PRIMARY ENDPOINTS: Analysis of HCRU outcomes and costs. RESULTS: Total costs were similar between the linezolid- (€17,782±€9,615) and vancomycin-treated patients (€17,423±€9,460) (P=.69). The renal failure rate was significantly lower in the linezolid-treated patients (4% vs. 15%; P<.001). The total costs tended to be higher in patients who developed renal failure (€19,626±€10,840 vs. €17,388±€9,369; P=.14). Among the patients who developed renal failure, HCRU (days on mechanical ventilation: 13.2±10.7 vs. 7.6±3.6 days; P=.21; ICU stay: 14.4±10.5 vs. 9.9±6.6 days; P=.30; hospital stay: 19.5±9.5 vs. 16.1±11.0 days; P=.26) and cost (€17,219±€8,792 vs. €20,263±€11,350; P=.51) tended to be lower in the linezolid- vs. vancomycin-treated patients. There were no statistically significant differences in costs per patient-day between cohorts after correcting for mortality (€1000 vs. €1,010; P=.98). CONCLUSIONS: From a Spanish perspective, there were no statistically significant differences in total costs between the linezolid and vancomycin pneumonia cohorts. The drug cost corresponding to linezolid was partially offset by fewer renal failure adverse events.

Diagnosis and treatment of bacteremia and endocarditis due to Staphylococcus aureus. A clinical guideline from the Spanish Society of Clinical Microbiology and Infectious Diseases (SEIMC).

Both bacteremia and infective endocarditis caused by Staphylococcus aureus are common and severe diseases. The prognosis may darken not infrequently, especially in the presence of intracardiac devices or methicillin-resistance. Indeed, the optimization of the antimicrobial therapy is a key step in the outcome of these infections. The high rates of treatment failure and the increasing interest in the influence of vancomycin susceptibility in the outcome of infections caused by both methicillin-susceptible and -resistant isolates has led to the research of novel therapeutic schemes. Specifically, the interest raised in recent years on the new antimicrobials with activity against methicillin-resistant staphylococci has been also extended to infections caused by susceptible strains, which still carry the most important burden of infection. Recent clinical and experimental research has focused in the activity of new combinations of antimicrobials, their indication and role still being debatable. Also, the impact of an appropriate empirical antimicrobial treatment has acquired relevance in recent years. Finally, it is noteworthy the impact of the implementation of a systematic bundle of measures for improving the outcome. The aim of this clinical guideline is to provide an ensemble of recommendations in order to improve the treatment and prognosis of bacteremia and infective endocarditis caused by S. aureus, in accordance to the latest evidence published.

Executive summary of the diagnosis and treatment of bacteremia and endocarditis due to Staphylococcus aureus. A clinical guideline from the Spanish Society of Clinical Microbiology and Infectious Diseases (SEIMC).

Bacteremia and infective endocarditis caused by Staphylococcus aureus are common and severe diseases. Optimization of treatment is fundamental in the prognosis of these infections. The high rates of treatment failure and the increasing interest in the influence of vancomycin susceptibility in the outcome of infections caused by both methicillin-susceptible and -resistant isolates have led to research on novel therapeutic schemes. The interest in the new antimicrobials with activity against methicillin-resistant staphylococci has been extended to susceptible strains, which still carry the most important burden of infection. New combinations of antimicrobials have been investigated in experimental and clinical studies, but their role is still being debated. Also, the appropriateness of the initial empirical therapy has acquired relevance in recent years. The aim of this guideline is to update the 2009 guidelines and to provide an ensemble of recommendations in order to improve the treatment of staphylococcal bacteremia and infective endocarditis, in accordance with the latest published evidence.

Community-acquired necrotizing pneumonia caused by methicillin-resistant Staphylococcus aureus ST30-SCCmecIVc-spat019-PVL positive in San Antonio de Areco, Argentina.

Community-acquired methicillin-resistant Staphylococcus aureus is the first cause of skin and soft tissue infections, but can also produce severe diseases such as bacteremia, osteomyelitis and necrotizing pneumonia. Some S. aureus lineages have been described in cases of necrotizing pneumonia worldwide, usually in young, previously healthy patients. In this work, we describe a fatal case of necrotizing pneumonia due to community-acquired methicillin-resistant S. aureus clone ST30-SCCmecIVc-spat019-PVL positive in an immunocompetent adult patient.

[Ceftaroline breakpoints]. / Puntos de corte de ceftarolina.

Ceftaroline is a new cephalosporin for parenteral use. Notable among its microbiological properties is its ability to inhibit penicillin-binding protein 2a of methicillin-resistant Staphylococcus aureus and its good in vitro activity against several microorganisms of clinical interest. The European Committee of Antimicrobial Susceptibility Testing (EUCAST) has defined both epidemiological breakpoints (defining wild-type populations that lack known acquired mechanisms of resistance) and clinical breakpoints for this compound. The Clinical and Laboratory Standards Institute (CLSI) has also defined clinical breakpoints. Based on the microbiological activity of ceftaroline, clinical categories have been defined for enterobacteria, S. aureus, Haemophilus influenzae, Streptococcus pneumoniae, and beta-hemolytic Streptococcus. EUCAST has also established breakpoints based on pharmacokinetic-pharmacodynamic criteria.

[Role of ceftaroline in skin and soft tissue infections]. / Papel de ceftarolina en infecciones de piel y partes blandas.

Skin and soft tissue infections (SSTI) are relatively common. Although most of these infections are mild, a few are severe, requiring hospital admission for intravenous antimicrobial therapy and, fairly frequently, surgery. These infections can be produced by any microorganism, but the most frequent is Staphylococcus aureus. Traditionally, the bacteria causing community-acquired SSTI have been sensitive to antimicrobial agents but this situation has changed with the dissemination of community-acquired microbial resistance, as has occurred in many countries with the increase in methicillin-resistant S. aureus (MRSA). These changes complicate empirical therapy and increase the risk of monotherapy being insufficient to cover all the diagnostic possibilities of SSTI. Within this epidemiological framework, ceftaroline, because of its activity against MRSA, can be used as empirical monotherapy for SSTI.

[Ceftaroline fosamil in community-acquired and nosocomial pneumonia]. / Ceftarolina fosamil en la neumonía comunitaria y nosocomial.

Community-acquired pneumonia (CAP) is a common infection in developed countries and causes a large number of hospital admissions and deaths. In recent years, the incidence of this disease has increased, caused by progressive population aging. Following the introduction of the conjugate vaccine against Streptococcus pneumoniae, there have been significant epidemiological changes that require close monitoring because of the possible emergence of new patterns of resistance. This article aims to review the role of ceftaroline fosamil, a new parenteral cephalosporin with antibacterial activity against Gram-negative and Gram-positive pathogens, in the treatment of pneumonia. Several in vitro and in vivo studies have shown the efficacy of ceftaroline fosamil against penicillin-resistant S. pneumoniae and methicillin-resistant Staphylococcus aureus (MRSA). Additionally, ceftaroline has shown similar efficacy and safety to ceftriaxone in the treatment of community-acquired pneumonia with severe prognosis (prognostic severity index III and IV) in two phase III clinical trials. Although a non-inferiority design was used for these clinical trials, some data suggest a superior efficacy of ceftaroline, with earlier clinical response and higher cure rate in infections caused by S. pneumoniae, making this drug particularly interesting for critically-ill patients admitted to the intensive care unit. Ceftaroline may also be considered for empirical and directed treatment of MRSA pneumonia.

[Clinical features and outcome of community-acquired methicillin-resistant Staphylococcus aureus pneumonia]. / Características clínicas y pronóstico de la neumonía adquirida en la comunidad causada por Staphylococcus aureus resistente a la meticilina.

INTRODUCTION: The aim of this study is to describe the epidemiological and clinical features, treatment and prognosis of community-acquired pneumonia (CAP) caused by methicillin-resistant Staphylococcus aureus (MRSA) in two different geographic regions where community-acquired MRSA (CA-MRSA) infections have different frequencies. METHODS: Observational study of patients admitted to two hospitals (one in Argentina, the other in Spain) between March 2008 and June 2012. RESULTS: We documented 16 cases of CAP caused by MRSA. MRSA accounted for 15 of 547 (2.7%) cases of CAP in Hospital Rodolfo Rossi and 1 of 1258 (0,08%) cases at the Hospital Universitari de Bellvitge (P ≤ .001). Most patients were young and previously healthy. Multilobar infiltrates, cavitation and skin and soft tissue involvement were frequent. All patients had positive blood cultures. Five patients required admission to the intensive care unit. Early mortality (≤ 48 hours) was 19%, and overall mortality (≤ 30 days) was 25%. CONCLUSION: CAP caused by MRSA causes high morbidity and mortality rates. It should be suspected in areas with a high prevalence of CA-MRSA infections, and especially in young and healthy patients who present with multilobar pneumonia with cavitation. Mortality is mainly related to septic shock and respiratory failure and occurs early in most cases.

[Skin and soft-tissue infections in hospitalized patients: epidemiology, microbiological, clinical and prognostic factors]. / Infecciones de piel y partes blandas en pacientes hospitalizados: factores epidemiológicos, microbiológicos, clínicos y pronósticos.

INTRODUCTION: Skin and soft-tissue infections (SSTIs) are a frequent cause of consultation in emergence services, and complicated cases require hospitalization. However there are few data in our setting about the clinical characteristics of these infections. MATERIAL AND METHODS: A retrospective review of hospital admitted patients with a diagnosis of folliculitis, cellulitis, erysipelas, abscesses, hidradenitis, furuncle, impetigo, fasciitis and Fournier's gangrene. Cases were extracted from the data base of diagnostic codes of the Archive and Clinical Documentation Department of Son Llàtzer Hospital from January 2002 to November 2011. RESULTS: We studied 996 episodes in 841 hospitalized patients with any diagnosis of SSTIs. Cellulitis/erysipelas (66.7%) was the most frequently diagnosed condition, with 77% of all SSTIs being community acquired, and the majority of patients had comorbidities, mainly diabetes (33%) and heart failure (17.7%). The most frequent isolated microorganism was S.aureus (35.1%), in 19 (12.9%) cases with methicillin-resistance (MRSA), 84.2% of them were nosocomial or health care acquired. Monotherapy with aminopenicillin with clavulanic acid was the empiric treatment most frequently used (35.5%). New antibiotics for Gram-positive cocci (linezolid, daptomycin, and tigecycline) were used in patients with comorbidities that presented more complications (P<.001) and more risk of mortality (P=.001). During admission 10.9% of patients died, but only in 2.7% of them mortality was related to the SSTIs. CONCLUSIONS: SSTIs attended most frequently in hospitalized patients are mainly cellulitis/erysipela, the majority community acquired. MRSA infections are mainly health care related. Use of new antibiotic for Gram-positive cocci was limited.

Skin infections caused by community-acquired methicillin-resistant Staphylococcus aureus: clinical and microbiological characteristics of 11 cases.

INTRODUCTION: Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is an emerging pathogen that causes skin and soft-tissue infections. OBJECTIVE: To describe the clinical characteristics of skin infections caused by CA-MRSA and correlations with the available demographic and microbiological data. MATERIAL AND METHODS: This was a descriptive study of patients with a microbiologically confirmed diagnosis of CA-MRSA infection treated in a dermatology department between June 2009 and December 2011. We recorded demographic details, the clinical characteristics of lesions, and the treatments used. RESULTS: We studied 11 patients (5 men and 6 women); 91% were under 40 years of age and had no relevant past medical history. The most common presentation was a skin abscess (with or without cellulitis). In all such cases, marked tissue necrosis and little or no purulent exudate was observed when the abscess was drained. Fifty percent of these abscesses had been treated previously with ß-lactam antibiotics, and in all cases the lesions resolved after surgical drainage, which was combined in 63% of cases with quinolones or cotrimoxazole. CONCLUSIONS: Today, skin infections due to CA-MRSA affect healthy young athletes who have no contact with healthcare settings. The most common presentation is a skin abscess characterized by marked tissue necrosis and little or no purulent exudate. In cases with these characteristics in susceptible patients, the involvement of CA-MRSA as the causative agent should be suspected. The abscesses should be drained whenever possible and, if necessary, antibiotic treatment should be prescribed; empirical use of ß-lactam antibiotics should be avoided.

[Infections caused by multi-resistant Gram-positive bacteria (Staphylococcus aureus and Enterococcus spp.)]. / Infecciones causadas por bacterias grampositivas multirresistentes (Staphylococcus aureus y Enterococcus spp.).

Methicillin -resistant Staphylocccus aureus (MRSA) and multirresistant entorococci are still problematic in nosocomial infections and new challenges have emerged for their containment. MRSA has increased the multiresistant profile; it has been described vancomycin and linezolid resistant isolates and isolates with decreased daptomycin susceptibility. Moreover, new clones (ST398) have emerged, initially associated with piggeries, and new mec variants (mecC) with livestock origin that escape to the detection with current molecular methods based on mecA gene have been detected. In enterococci, linzeolid resistant isolates and isolates with deceased susceptibility to daptomycin have been described. Moreover, ampicillin resistant Enterococcus faecium due to ß-lactamase production has been recently found in Europe. Control of MRSA isolates and multiresistant enteroccocci should combined antibiotic stewardship strategies and epidemiological measures, including detection of colonized patients in order to reduce colonization pressure and their transmission.

[Staphylococcus aureus nasal colonization in medical students: importance in nosocomial transmission]. / Colonización nasal por Staphylococcus aureus en estudiantes de medicina: importancia en la transmisión hospitalaria.

BACKGROUND: Staphylococcus aureus is the main pathogen causing nosocomial infections. Health professionals, including medical students, could be a source of transmission. The aims of the study were to determine the rate of nasal carriage of S.aureus susceptible and resistant to methicillin (MRSA) and evaluate the knowledge and adherence that students had about hand hygiene. METHODS: The study included medical students attached to the Hospital Universitario 12 de Octubre (Madrid, Spain). We collected samples from both nasal vestibules, and the antimicrobial susceptibility was determined on all isolates. Data collection was performed using a self-administered questionnaire that included risk factors for colonization, hygiene habits and knowledge of hand hygiene protocols. RESULTS: Of the 140 students included, 55 (39.3%) were colonized by S.aureus, and 3 (2,1%) by MRSA. The exposure to antibiotics in the last 3 months was lower in colonized students (12.3% vs. 25.9%, P=.03). Self-assessment showed that 56.4% of students almost never washed their hands before to attending to the first patient, and only 38.6% always washed after examining patients. More than a third (35.7%) ignored the hand hygiene protocol, and 38.6% had not received specific formation. CONCLUSIONS: Medical students should be included in hospital infection control programs. Hand hygiene training should be given to students before they begin their practices in the hospital.

[Significant increase in the colonisation of Staphylococcus aureus among medical students during their hospital practices]. / Aumento significativo de la colonización por Staphylococcus aureus entre los estudiantes de medicina durante la realización de las prácticas en el hospital.

INTRODUCTION: Staphylococcus aureus is a pathogen of major concern. The emergence of methicillin-resistant S. aureus (MRSA) has increasingly complicated the therapeutic approach of hospital-acquired infections. Surveillance of MRSA and control measures must be implemented in different healthcare settings, including screening programs for carriers. Our first aim was to determine the prevalence of methicillin-susceptible S. aureus (MSSA) and MRSA nasal carriage in medical students from the Clínico San Carlos Hospital (Madrid). As the MRSA carrier rate in healthcare workers is higher than in the general population, we hypothesised that carrier rate could be increased during their clinical practice in their last three years. METHODS: We performed an epidemiologic al study of the prevalence of S. aureus colonisation among a group of medical students, who were sampled in 2008 in their third-year, and in 2012 when this class was in its sixth year. RESULTS: We have found a significant increase in MSSA carriage, from 27% to 46%. There were no MRSA colonisations in the third-year, but one was found in the sixth-year group. The large majority of strains (89%) of strains were resistant to penicillin, and 27% to erythromycin and clindamycin. As 19 coagulase-negative Staphylococcus MR were also identified, a horizontal transfer of genes, such as mecA gene to S. aureus, could have occurred. CONCLUSIONS: Medical students are both, at risk for acquiring, and a potential source of nosocomial pathogens, mainly MSSA. Therefore, they should take special care for hygienic precautions, such as frequent and proper hand washing, while working in the hospital.