Methicillin-sensitive S. Aureus Group Research Articles

A Rare Case of Panton-Valentine Leukocidin-Related Cervical Empyema

Abstract Staphylococcus aureus is found in the normal skin and mucosa of approximately 30% of healthy populations and is the most common pathogen in human disease associated with bacteria. They are divided into methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). The S. aureus strains carrying the Panton-Valentine leukocidin genes (SA-PVL) were initially believed to belong to the MRSA group; however, recent reports showed they also belonged to the MSSA group (MSSA-PVL). SA-PVL is common in skin and soft-tissue infections but rare in musculoskeletal infections, especially in spondylodiscitis. We are reporting a case suffering from cervical spondylodiscitis and epidural abscess associated with MSSA carrying the Panton-Valentine leukocidin genes.

Risk Factors Associated with Methicillin Resistance in Hospitalized Newborn Infants with Staphylococcus aureus Infection.

BackgroundAn increasing number of infections due to methicillin-resistant Staphylococcus aureus (S. aureus) have been reported worldwide. To explore the risk factors associated with methicillin-resistance among the neonates with confirmed S. aureus infections and thereby to help selection of appropriate empirical antibiotics.MethodsWe compared a group of hospitalized neonates with culture confirmed methicillin-resistant S. aureus (MRSA) infections to a group with methicillin-sensitive S. aureus (MSSA) based on antimicrobial susceptibility reports. We used multivariable regression analysis to determine the risk factors for neonatal MRSA infections.ResultsThere was no difference in the ratio of local to systemic infections or mortality between the two groups. However, the total hospitalization days and the medical care expenses in the MRSA group were significantly increased when compared to that of the MSSA group. Prior use of antibiotics for more than 48 hours was an independent risk factor for neonatal acquisition of MRSA infections, while exclusive breast milk feeding was a protective factor against MRSA infections.ConclusionRestrictions on antibiotic abuse and promotion of breast milk feeding may protect newborns from MRSA infections. Prior history of antibiotic use and exclusive breast milk feeding may be important factors to consider in the selection of appropriate empirical antibiotics for use in neonates prior to the availability of the results of antimicrobial susceptibility testing.

Staphylococcus Aureus Bacteremia Due to Central Venous Catheter Infection: A Clinical Comparison of Infections Caused by Methicillin-Resistant and Methicillin-Susceptible Strains.

Objectives: Staphylococcus aureus bacteremia has a mortality rate of 20-40% and is mainly caused by central venous catheter (CVC) infection. We aimed to investigate differences between patients with methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) bacteremia due to CVC infection.Methods: This retrospective study, of data collected between August 2004 and March 2016 at a single Tokyo hospital, compared the clinical background characteristics, complications, and 60-day mortality rates with positive peripheral blood cultures and positive semiquantitative cultures. MRSA carrier is defined as those with a history of MRSA detection by skin, urine, or sputum culture.Results: The median ages for the 17 MRSA and 19 MSSA patients were 72 and 55 years, respectively (P < 0.01). The occurrences of baseline disease (MRSA vs. MSSA) were 59% vs. 16% (P = 0.01), respectively, while those of complications, including septic shock, were 48% vs. 16% (P = 0.07), respectively. Catheter placement duration, time from fever onset to CVC removal, and time from fever onset to antimicrobial therapy initiation were similar in both groups. Sixty-day mortality rates were 35% and 5.3% (P = 0.04) in the MRSA and MSSA groups, respectively.Conclusion: MRSA carriers and older patients were at higher risks of CVC infection than MSSA bacteremia patients. Patients with MRSA bacteremia had higher septic shock and 60-day mortality rates despite appropriate antimicrobial therapy.

Characterisation of antibiotic resistance, virulence, clonality and mortality in MRSA and MSSA bloodstream infections at a tertiary-level hospital in Hungary: a 6-year retrospective study

BackgroundStaphylococcus aureus bloodstream infections (BSI) cause significant morbidity and mortality due to the frequent antibiotic resistance, toxin and adhesin production of the bacterium. These characteristics differ significantly in methicillin resistant (MRSA) and methicillin sensitive S. aureus (MSSA) and also among isolates of different MRSA clones, contributing to the outcome of S. aureus bacteraemia.MethodsIn this study, all MRSA BSI isolates from Semmelweis University, Budapest, Hungary, isolated between 2011–2016 and the same number of matched MSSA (overall 306 isolates) were characterised in terms of antibiotic susceptibility, virulence genes, clonality and their association with all-cause 30-day mortality. Effect of patient related variables, such as age, gender and comorbidities were also investigated.ResultsST22-MRSA-IV and ST5-MRSA-II were the most prevalent clones in our study. SCCmec I isolates showed the highest resistance rates and SCCmec II carried most virulence genes. Infections caused by SCCmec IV isolates were associated with the highest mortality rate (42.2%), despite the similar comorbidity rates of the different patient groups. All-cause 30-day mortality was 39.9% in the MRSA and 30.7% in the MSSA group. Increased teicoplanin MIC was associated with high mortality rate. Resistance to ciprofloxacin, erythromycin and clindamycin was common in MRSA, whereas MSSA isolates were more sensitive to all antibiotics with the exception of doxycycline. All MRSA isolates were sensitive to glycopeptides and linezolid; resistance to rifampicin and sulfamethoxazole-trimethoprim was low. MRSA isolates carried more adhesion genes, superantigens were more frequent in MSSA. Panton-Valentine leukocidin was found in 2.3% of the isolates.ConclusionThis study provides insight into the clonal composition and associated mortality of BSI S. aureus isolates in Hungary. The results suggest that the outcome of the infection is determined by the antibiotic resistance, genotype of the bacterium, and patient-related factors; rather than the virulence factors carried by the bacteria.

Is methicillin-resistant Staphylococcus Aureus infection associated with higher mortality and morbidity in hospitalized patients? A cohort study of 551 patients from South Western India.

PurposeTo determine morbidity and mortality of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) infections in a tertiary health care facility.MethodsA cohort study among hospitalized adult patients with culture proven MRSA or MSSA monoinfection were recruited in a tertiary referral center in South India from November 2011 to December 2012.ResultsOf total 551 subjects, 284 (52%) had MRSA and 267 (48%) MSSA infection. A total of 184 (65%) subjects had health care-associated MRSA (HA-MRSA) and 100 (35%) community-associated MRSA (CA-MRSA). Chronic kidney disease and recent antibiotic use had significant association with MRSA. MRSA patients had significant respiratory infection (OR 2.24 [1.04, 5.16]) and bacteremia (OR 2.24 [10.40, 5.16]), relative to MSSA. MSSA group had better survival function compared to MRSA group (P=0.028). Median duration of ICU stays were 5 days (IQR 4, 8) and 2 days (IQR 2, 2) in MRSA and MSSA, respectively. Complications such as acute kidney injury, sepsis, multiorgan dysfunction, need for supportive measures were more in the MRSA group.ConclusionMRSA imposes a huge burden in Indian scenario and HA-MRSA remains the main culprit. Patients with history of chronic kidney disease and recent use of antibiotics were found to be at a higher risk. Patients with MRSA infections tend to have poorer outcomes in terms of longer hospital stay, greater complications, and mortality.

Comparación de las características y curso clínico de la endocarditis infecciosa por Staphylococcus aureus meticilino sensible versus meticilino resistente

IntroductionStaphylococcus aureus is one of the most common sources of infectious endocarditis. There are few studies in Latin America that report on the differences between the methicillin resistance profiles. ObjectiveTo describe the characteristics and clinical course of patients with methicillin-sensitive S. aureus (MSSA) compared to methicillin-resistance S. aureus (MRSA) MethodsAn observational, retrospective study was conducted on a historical cohort of adult patients with a confirmed diagnosis of endocarditis between the years 2011 and 2015. Patients positive for S. aureus were selected and the characteristics and clinical course and the cases of MSSA were compared with those of MRSA. ResultsA total of 86 patients with endocarditis were included, of whom 28 (33%) had an infection due to S. aureus, and 21 (75%) had endocarditis due to methicillin-sensitive S. aureus, and 7 (25%) due to MRSA. In the MSSA group, 11 (52.3%) were infections associated with health care. The majority (85.7%) of cases of MRSA were community acquired. The endocarditis mortality due to MSSA was higher than that caused by MRSA (33.3% vs. 14%). ConclusionsS. aureus continues to be the most common agent in endocarditis, with MSSA being more common. The embolic events and the severity were greater in MSSA. The majority of endocarditis due to MRSA is acquired in the community, and for this reason it is suggested starting empirical cover against MRSA in all cases of community acquired endocarditis.

Clinical outcomes and antibiotic susceptibilities of Staphylococcus aureus endophthalmitis.

To compare the antibiotic susceptibilities and visual acuity (VA) outcomes in endophthalmitis caused by methicillin-resistant (MRSA) versus methicillin-sensitive S. aureus (MSSA). The records of 34 cases of S. aureus endophthalmitis at The New York Eye and Ear Infirmary from Jan 1997 to June 2011 were reviewed. Antibiotic susceptibility profiles over time and VA at presentation and at 3, 6, and ≥12months were recorded. S. aureus isolates were grouped based on oxacillin resistance. Of the 34 cases, 15 (44%) were MRSA and 19 (56%) MSSA. Median presenting VA was hand motions (logMAR 4.0) in both the MRSA and MSSA groups. There was no statistically significant difference in VA between the MRSA and MSSA groups at 3, 6, or ≥12months. No MRSA isolates were resistant to vancomycin or gentamicin. While over 85% of MRSAisolates tested for fourth-generation fluoroquinolones were resistant, just 10 % MSSA isolates tested were resistant. There was a trend suggesting an increase in the proportion of MRSA isolates compared to MSSA isolates over the course of the study period. There was no statistical difference in short- or long-term VA outcomes between the MRSA and MSSA groups at any time point. Resistance to fourth-generation fluoroquinolones was present in over 85% of MRSA isolates, but just 10 % of MSSA isolates. An increasing proportion of MRSA amongst S. aureus isolates was noted over the course of the study period.

Staphylococcus aureus Keratitis: A Review of Hospital Cases

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) infection is an important public health issue. The study aimed to characterize the patient demographics, clinical features, antibiotic susceptibility, and clinical outcomes of keratitis caused by S. aureus, and to make a comparison between MRSA and methicillin-sensitive S. aureus (MSSA) isolates.Methodology/Principal findingsPatients (n = 59) with culture-proven S. aureus keratitis treated in Chang Gung Memorial Hospital between January 1, 2006, and December 31, 2010, were included in our study. Patients' demographic and clinical data were retrospectively reviewed. Twenty-six MRSA (44%) and 33 MSSA (56%) isolates were collected. The MRSA keratitis was significantly more common among the patients with healthcare exposure (P = 0.038), but 46.2% (12/26) of patients with MRSA keratitis were considered to have community-associated infections. All isolates were susceptible to vancomycin. MRSA isolates were significantly more resistant to clindamycin, erythromycin, and sulfamethoxazole/trimethoprim. Ocular surface disease was a significant risk factor for MRSA keratitis (P = 0.011). Visual outcome did not differ significantly between the MRSA and MSSA groups. However, age (B = 0.01, P = 0.035, 95% confidence interval [CI]: 0.001–0.019) and visual acuity at presentation (B = 0.749, P<0.001, 95% CI: 0.573–0.926) were significantly correlated with visual outcome.Conclusions/SignificanceOcular surface disease is an important predisposing factor for S. aureus keratitis, especially for MRSA infections. Advanced age and poor visual acuity at presentation are important prognostic indicators for poor visual outcome in S. aureus keratitis. Oxacillin resistance may not be a significant prognostic indicator.

Necrotizing Fasciitis Caused by Staphylococcus aureus

Staphylococcus aureus is an uncommon causative agent of monomicrobial necrotizing fasciitis, but we have noted several cases over the years. The patients treated for necrotizing fasciitis between January 1998 and December 2008 in our institution were identified, and their medical records were reviewed. Of 105 necrotizing fasciitis cases during the study period, 18 were caused by monomicrobial S. aureus infection (17%). The median age was 62 years (range, 12-81 years). Among this cohort, 10 patients had coexisting medical conditions or risk factors, including diabetes and hypertension. Lower limbs and upper limbs are the most commonly involved sites. Among the bacterial isolates from these cases, 8 were methicillin-sensitive S. aureus (MSSA) and 10 were methicillin-resistant S. aureus (MRSA). One patient died in the MSSA group, and 5 patients died in the MRSA group. The mortality rate and other clinical characteristics were not significantly different between the 2 groups. However, all MRSA necrotizing fasciitis developed after the year 2000, and it was significantly different from MSSA necrotizing fasciitis that predominantly took place before the year 2000. In conclusion, S. aureus is an important pathogen of monomicrobial necrotizing fasciitis, and MRSA has emerged as the predominant causative agent in recent years. Therefore, MRSA-directed antibiotic therapy should be considered when treating patients suspected with necrotizing fasciitis in endemic areas.

Virulence genes and genotypic associations in nasal carriage, community-associated methicillin-susceptible and methicillin-resistant USA400 Staphylococcus aureus isolates.

It is not well understood why strains of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), a major cause of skin and soft tissue infections, became successful so quickly, overtaking the place of methicillin-sensitive S. aureus (MSSA) in many communities. To evaluate the genetic basis of differences in their virulence traits, 293 S. aureus isolates consisting of three cohorts, genotypically defined clinical CA-MRSA (n = 77), clinical MSSA (n = 103), and nasal carriage MSSA (n = 113), collected over a 19-year period in two Midwestern states in the United States, were (i) extensively genotyped and (ii) screened for 40 known virulence genes which included those for enterotoxins, leukocidins, hemolysins, and surface proteins and several newly identified putative toxin genes from the USA400 lineage of CA-MRSA. Genotypically, nasal carriage and clinical MSSA isolates were much more diverse than was the CA-MRSA group, which was found to be of USA400 lineage only. Virulence gene profiles of the three groups showed that CA-MRSA strains harbored significantly higher percentages (≥95%; P value, <0.05) of the sea, sec, sec4, seg2, seh, sek, sel, sel2, ear, ssl1, lpl10, lukSF-PV, lukD, lukE, and clfA genes than did the carriage and the clinical MSSA group (range, 0% to 58%). Genes of the enterotoxin gene cluster, seg, sei, sem, sen, and seo, were present in the clinical and carriage isolates but not in the CA-MRSA group. These results suggest that the presence of additional virulence factors in USA400 CA-MRSA strains compared to the nasal carriage and clinical MSSA strains probably contributed to their enhanced virulence.

Methicillin-resistant versus methicillin-sensitive Staphylococcus aureus infective endocarditis

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) infective endocarditis (IE) is increasing. This study compared clinical characteristics and mortality in patients with methicillin-sensitive S. aureus (MSSA) IE versus MRSA IE, based on a prospectively collected series of 72 consecutive patients with definite S. aureus IE according to the modified Duke criteria between June 2000 and December 2006. Sixteen of 72 IE patients (22%) were caused by MRSA. Nosocomial origin, surgical site infection, surgery in the previous 6 months, the presence of a catheter and persistent bacteremia were significantly associated with MRSA. MSSA patients had significantly more unknown origin of bacteremia and experienced a significantly higher rate of major embolism than MRSA patients. MSSA patients underwent more frequently combined surgical and antimicrobial therapy, and MRSA patients were treated more frequently with antimicrobial therapy due to a contraindication to surgery. The 6-month mortality was higher in patients with MRSA than MSSA. In the MSSA group treated with antimicrobial therapy without an indication to surgery, all patients survived, and in the combined surgical and antimicrobial group 29% died. The mortality in MRSA patients was lowest if combined surgical and antimicrobial therapy was performed. Both in MSSA and MRSA patients with antimicrobial therapy due to a contraindication to surgery, the mortality was extremely high. These data suggest that in S. aureus IE patients with a nosocomial origin, the presence of a catheter or recent surgery, initial therapy should include antimicrobial agents active against MRSA. Antimicrobial therapy alone with close monitoring of the therapeutic effect and signs of complicated course is an acceptable approach in selected patients with MSSA IE. Denial of surgery because of local or general factors in patients that meet criteria for surgical intervention in acute IE is prognostically ominous.

Presence of methicillin resistant Staphylococcus aureus in respiratory cultures from cystic fibrosis patients is associated with lower lung function

The prevalence of methicillin resistant Staphylococcus aureus (MRSA) infections is increasing in both the general population and cystic fibrosis (CF) patients. We hypothesized that MRSA infection of the conductive airways as seen in CF would be associated with more severe disease than that seen with methicillin sensitive S. aureus (MSSA). To test this hypothesis, we used data from the Epidemiologic Study of Cystic Fibrosis (ESCF), a large observational study of CF patients in North America, to compare CF patients with MRSA in their respiratory tract cultures to those with MSSA. During a 1-year time period from January 1, 2001 to December 31, 2001, data from 20,451 patients were collected by the ESCF, and 1,834 (7.5%) patients had respiratory tract cultures that were positive for S. aureus only. Compared to patients with MSSA only, patients with MRSA only had significantly more airflow obstruction, as measured by forced expiratory volume in 1 sec (FEV1). The mean FEV1 for patients 6-17 years old with MRSA was 80.7% predicted compared to 89.4% in the MSSA group (P<0.001). The likelihood of hospitalization and treatment with oral, inhaled, and intravenous antibiotics were all significantly increased in patients with MRSA compared to those with MSSA. Similar results were seen in patients >or=18 years old. The results of our study highlight the growing clinical impact of MRSA infections in CF patients.

Clinical features of head and neck cancer patients with methicillin-resistant Staphylococcus aureus

Conclusions. The risk factors for methicillin-resistant Staphylococcus aureus (MRSA) detection in head and neck cancer patients are the duration of hospitalization, intravenous hyperalimentation, prior antibiotic use, and the coexistence of other pathogens. Objectives. To shed light on the clinical characteristics of MRSA-positive inpatients with head and neck cancers. The secondary goal was to evaluate risk factors for MRSA detection in comparison with methicillin-sensitive S. aureus (MSSA). Patients and methods. Sixty-one consecutive inpatients with head and neck cancers with S. aureus detection were analyzed based on their medical records. The antimicrobial susceptibility of isolated S. aureus was tested by the broth microdilution method. Results. MRSA and MSSA were detected in 46 (75.4%) and 15 (24.6%) of the 61 patients, respectively. There was no significant difference in the male/female ratio, age, primary site, comorbidity, cancer stage, cancer treatment, or 5-year survival rate between the MRSA and MSSA groups. Compared with the MSSA group, the MRSA group had significantly longer hospitalization periods and intervals between admission and MRSA detection, as well as significantly greater likelihood of intravenous hyperalimentation, prior antibiotic use, and co-isolation of other pathogens. Isolated strains of MRSA were thoroughly sensitive to vancomycin and arbekacin and moderately sensitive to minocycline.

Staphylococcus aureus Endocarditis: The Grady Memorial Hospital Experience

Staphylococcus aureus is a common cause of endocarditis. Previous studies have shown that the mortality rate associated with S aureus endocarditis remains high, and methicillin resistance is becoming more prevalent. Over the past 4 years, 283 patients with suspected endocarditis were referred to the cardiology department of Grady Memorial Hospital for echocardiography. Their clinical course and demographic information was entered into a database. Among these patients, 87 (30.6%) were confirmed to have endocarditis, with 41 (47.1%) of them culture positive for either methicillin-resistant (MRSA) or methicillin-sensitive S aureus (MSSA). Of these patients, 14 were MRSA culture positive, and 27 were MSSA culture positive. These two groups were compared with respect to demographic information and morbidity and mortality outcomes. The MRSA and MSSA groups were found to be similar upon analysis in all baseline characteristics. There was a non-statistical trend among the two groups in origin of infection, as the MRSA group tended toward nosocomial infection more often. Outcomes, including surgery, death, and complications were also found to be similar between the two groups. There does not seem to be difference in the outcome of MRSA versus MSSA endocarditis. Nosocomial infection may predispose patients to MRSA endocarditis, but a larger study with a greater sample size is necessary to evaluate these questions more accurately.

Staphylococcus aureus bacteremia and endocarditis: the Grady Memorial Hospital experience with methicillin-sensitive S aureus and methicillin-resistant S aureus bacteremia

Background Staphylococcus aureus has become the leading cause of endocarditis in most published series, and nosocomial acquisition is becoming more frequent. Previous studies involved community acquired methicillin-sensitive S aureus (MSSA), but recently, methicillin-resistant S aureus(MRSA) infection has increased. This may reflect the growing presence of this microorganism in clinical practice. Few data exist comparing the relative rates of endocarditis with MSSA and MRSA bacteremia. The purpose of this study was to compare these rates in a bacteremic population referred for diagnostic echocardiography. Methods Since July 1999, the demographic and clinical information of 104 consecutive patients with at least 2 blood cultures with positive results for S aureus who were referred for echocardiography to be evaluated for endocarditis at Grady Memorial Hospital (Atlanta, Ga) have been entered into a database. This database has further been restricted to patients who have undergone either a transesophageal echocardiogram or a transthoracic echocardiogram. Results Of the 104 patients with S aureus bacteremia, 53 had an infection of MSSA and 51 had an infection of MRSA. There were 33 patients (31.7%) with echocardiographically confirmed endocarditis, 23 patients (43.4%) in the MSSA group versus10 patients (19.6%) in the MRSA group ( P <.009). Community-acquired MSSA bacteremia was the cause of most of the community-acquired S aureus endocarditis (20 patients [87%] vs 3 patients [30%], P = .004), and the nosocomial-acquired MRSA bacteremia was the cause of most of the nosocomial-acquired S aureus endocarditis (3 patients [13%] vs 7 patients [70%], P = .0001). Conclusion Our study confirms that S aureus bacteremia is associated with high rates of endocarditis. MSSA bacteremia is associated with higher rates of endocarditis than MRSA. Community MSSA is the cause of most of the community endocarditis, whereas nosocomial MRSA is the cause of most of the MRSA endocarditis. Patients with S aureus bacteremia should be aggressively evaluated for endocarditis.

Staphylococcal bacteraemia: the hospital or the home? A review of Staphylococcus aureus bacteraemia at Concord Hospital in 1993.

To examine the risk factors for, and the complications and mortality of, Staphylococcus aureus bacteraemia. A retrospective case review of patients with S. aureus bacteraemia in 1993 diagnosed at the Concord Repatriation General Hospital, Sydney. Of 104 cases reviewed, 32 were due to methicillin resistant S. aureus (MRSA), 73 were due to methicillin sensitive S. aureus (MSSA) and one was a dual infection. Twenty-eight of the bacteraemias were community-acquired, including one case of MRSA, and 76 were hospital-acquired; 38% had an implanted prosthetic device or graft. The average age (68 years), incidence of underlying diseases and hospitalisation in the past month (26%) did not differ between MRSA and MSSA groups. MRSA was more likely in patients with recent broad-spectrum antibiotic use (53% vs 0, p < .01). Vascular access was the commonest source of sepsis (61%) but in community-acquired cases the source was unknown in 50%. Use of central line access was more predictive of MRSA infection (75% vs 49%, p = .018). In hospital-acquired infection, MRSA sepsis occurred later in the course of the admission (26 days vs eight days, p < .01). Directly attributable mortality was highest in MRSA and community-acquired MSSA infection (9% and 11%) compared with hospital-acquired MSSA infection (1%). Nosocomial S. aureus bacteraemia, particularly MRSA, is a major source of preventable morbidity, which could be addressed by improved infection control of MRSA, antibiotic use and attention to central line catheter use.

A Comparison of Clinical Virulence of Nosocomially Acquired Methicillin-Resistant and Methicillin-Sensitiye Staphylococcus aureus Infections in a University Hospital

To compare the clinical virulence of nosocomially acquired methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S aureus (MSSA) infections in 1989. A retrospective comparison of host factors, in-hospital exposures, sites of infections, and outcomes of patients with nosocomial MRSA and MSSA infections. University of Illinois Hospital, Chicago, Illinois. Forty-four adult patients with nosocomial S aureus infections. The 22 MRSA-infected and 22 MSSA-infected persons were similar regarding mean age, gender, underlying diseases, and exposure to surgery. Before developing infection, MRSA-infected persons were more likely to have received antibiotics (73% compared with 27%, odds ratio = 7.1, 95% confidence interval [CI95] = 2.0-25.8 p = .003) and to have stayed in the hospital > 2 weeks (64% compared with 18%, odds ratio = 7.9, CI95 = 2.0-31.6, p = .002). Bacteremia was the most common presentation in the MRSA and MSSA groups (55% and 59%, respectively). Infectious complications and death were infrequent in both groups. MRSA and MSSA strains infect patients with similar demographic features and underlying diseases, but MRSA infections are significantly more common among patients with previous antibiotic therapy and a prolonged preinfection hospital stay. Clinical presentations and outcomes did not differ significantly between the 2 groups. Thus, similar to studies in the early 1980s, our findings do not suggest greater intrinsic virulence of MRSA.