Changing epidemiology of community-onset methicillin-resistant Staphylococcus aureus bacteremia.

OBJECTIVES: To review cases of community-onset Staphylococcus aureus bacteremia and to evaluate whether the risk factors and epidemiology of methicillin-resistant S. aureus (MRSA) bacteremia have changed from early reports. DESIGN: Retrospective case-comparison study of community-onset MRSA (n = 26) and methicillin-susceptible S. aureus (MSSA) (n = 26) bacteremias at our institution. SETTING: A 600-bed urban academic medical center. PATIENTS: Twenty-six patients with community-onset MRSA bacteremia were compared with 26 patients with community-onset MSSA bacteremia. Molecular analysis was performed on S. aureus isolates from the 26 MRSA cases as well as from 13 cases of community-onset S. aureus bacteremia from 1980 and 9 cases of nosocomial S. aureus bacteremia from 2001. RESULTS: The two groups were similar except that patients with MRSA bacteremia were more likely to have presented from a long-term-care facility (26.9% vs 4%; P = .05) and to have had multiple admissions within the preceding year (46% vs 15%; P = .03). Clamped homogeneous electric fields analysis of MRSA isolates from 1982 revealed predominantly that one clone was the epidemic strain, whereas there were 14 unique strains among current community-onset isolates. Among current nosocomial isolates, 3 patterns were identified, all of which were present in the community-onset cases. CONCLUSIONS: Previously described risk factors for MRSA acquisition may not be helpful in predicting disease due to the polyclonal spread of MRSA in the community. Unlike early outbreaks of MRSA in patients presenting from the community, current acquisition appears to be polyclonal and is usually related to contact with the healthcare system.     

Carriage of Staphylococcus aureus and of gram-negative bacilli resistant to third-generation cephalosporins in cirrhotic patients: a prospective assessment of hospital-acquired infections.

OBJECTIVE: To study the relation between Staphylococcus aureus nasal and stool colonization, stool carriage of gram-negative bacilli resistant to third-generation cephalosporins (CephR), and subsequent infections during hospitalization. DESIGN: Prospective study. PATIENTS: 551 cirrhotic patients with 589 consecutive hospital stays. All patients were screened within 48 hours of admission; 589 nasal swabs, 417 stool specimens, and 589 urine samples were analyzed. RESULTS: Carriage rates were 18.8% for methicillin-sensitive S aureus (MSSA), 16.3% for methicillin-resistant S aureus (MRSA), and 13.7% for CephR. We observed 87 episodes of spontaneous bacterial peritonitis, 63 cases of bacteremia, and 167 urinary tract infections occurred. Only 1 case of bacteremia and 4 urinary tract infections due to CephR occurred in patients carrying the same organism in their stools. The risk of MRSA ascitic fluid infections, bacteremia, and urinary tract infections was 3.1% versus 1% (not significant), 8.3% versus 0.8% (P<.001), and 11.4% versus 0.6% (P<.001) in carriers and noncarriers, respectively. Pulsed-field gel electrophoresis (PFGE) of isolates from 16 patients infected by MSSA (3 cases) and MRSA (13 cases) demonstrated that the colonizing strains matched the invasive strains in the 3 MSSA cases and in 8 of 13 MRSA cases. CONCLUSION: Carriage of CephR strains is not associated with subsequent infection by these organisms in hospitalized cirrhotic patients. In contrast, MRSA carriage was an important risk factor for MRSA bacteremia and urinary tract infection.     

The impact of methicillin resistance in Staphylococcus aureus bacteremia on patient outcomes: mortality, length of stay, and hospital charges.

OBJECTIVE: To evaluate the impact of methicillin resistance in Staphylococcus aureus on mortality, length of hospitalization, and hospital charges. DESIGN: A cohort study of patients admitted to the hospital between July 1, 1997, and June 1, 2000, who had clinically significant S. aureus bloodstream infections. SETTING: A 630-bed, urban, tertiary-care teaching hospital in Boston, Massachusetts. PATIENTS: Three hundred forty-eight patients with S. aureus bacteremia were studied; 96 patients had methicillin-resistant S. aureus (MRSA). Patients with methicillin-susceptible S. aureus (MSSA) and MRSA were similar regarding gender, percentage of nosocomial acquisition, length of hospitalization, ICU admission, and surgery before S. aureus bacteremia. They differed regarding age, comorbidities, and illness severity score. RESULTS: Similar numbers of MRSA and MSSA patients died (22.9% vs 19.8%; P = .53). Both the median length of hospitalization after S. aureus bacteremia for patients who survived and the median hospital charges after S. aureus bacteremia were significantly increased in MRSA patients (7 vs 9 days, P = .045; 19,212 dollars vs 26,424 dollars, P = .008). After multivariable analysis, compared with MSSA bacteremia, MRSA bacteremia remained associated with increased length of hospitalization (1.29 fold; P = .016) and hospital charges (1.36 fold; P = .017). MRSA bacteremia had a median attributable length of stay of 2 days and a median attributable hospital charge of 6916 dollars. CONCLUSION: Methicillin resistance in S. aureus bacteremia is associated with significant increases in length of hospitalization and hospital charges.     

Rates of carriage of methicillin-resistant and methicillin-susceptible Staphylococcus aureus in an outpatient population.

OBJECTIVES: To assess the prevalence of and the clinical features associated with asymptomatic Staphylococcus aureus colonization in a healthy outpatient population, and to compare the characteristics of colonizing methicillin-resistant S. aureus (MRSA) strains with those of strains causing infection in our community and hospital. SETTING: Outpatient military clinics. METHODS: Specimens were obtained from the nares, pharynx, and axillae of 404 outpatients, and a questionnaire was administered to obtain demographic and risk factor information. MRSA strains were typed by pulsed-field gel electrophoresis (PFGE) and evaluated for antibiotic susceptibility. Antibiograms of study MRSA strains were compared with those of MRSA strains causing clinical illness during the same time period. RESULTS: Methicillin-susceptible S. aureus (MSSA) colonization was present in 153 (38%) of the 404 asymptomatic outpatients, and MRSA colonization was present in 8 (2%). Detection of colonization was highest from the nares. No clinical risk factor was significantly associated with MRSA colonization; however, a tendency was noted for MRSA to be more common in men and in those who were older or who had been recently hospitalized. All colonizing MRSA strains had unique patterns on PFGE. In contrast to strains responsible for hospital infections, most colonizing isolates of MRSA were susceptible to oral antibiotics. CONCLUSIONS: MRSA and MSSA colonization is common in our outpatient population. Colonization is best detected by nares cultures and most carriers of MRSA are without apparent predisposing risk factors for acquisition. Colonizing isolates of MRSA are heterogeneous and, unlike nosocomial isolates, often retain susceptibility to other non-beta-lactam antibiotics.     

MRSA呼吸系统医院感染的分子流行病学调查

目的对广州呼吸疾病研究所2001年7月～2003年3月间,金黄色葡萄球菌引起的呼吸系统医院感染进行病原学监测. 方法收集临床分离菌株,应用脉冲场凝胶电泳的方法(PFGE)进行分型,确定菌株亲缘关系,结合临床资料分析. 结果在各种呼吸道采集标本中共收集到76株金黄色葡萄球菌,耐甲氧西林金黄色葡萄球菌(MRSA)68株,占金黄色葡萄球菌检出率89.47%,MRSA在我所病区中引起59例医院感染,属于暴发形式发病的有23例,属于聚集性发病的有19例,散发病例17例,PFGE分型表明,绝大多数MRSA属于同一型(A型)共有60株,其中A1亚型28株,A2亚型14株,A3亚型17株,A4亚型1株. 结论MRSA引起的呼吸系统医院感染十分严重,并主要由少数菌株的传播引起,及时采取有效措施控制MRSA的流行和播散非常必要.     

Molecular characterization of methicillin-resistant Staphylococcus aureus (MRSA) in a university hospital in Italy

The molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in a university hospital in Italy was studied in a five-month period in 1996, during which all S. aureus isolated were collected. All MRSA isolates (95) and a sample of methicillin-susceptible S. aureus (20) were typed with a variety of phenotypic and genotypic methods. Clonal identities were determined by pulsed-field gel electrophoresis (PFGE) of chromosomal SmaI digests and, for MRSA isolates, by probing ClaI digests with a mecA probe and a Tn554 probe. Overall, MRSA represented 32.3% of all isolates, with very high percentages from the intensive care units (adult and neonatal). PFGE after restriction with SmaI resolved genomic DNA of 95 MRSA strains into 26 major PFGE patterns. The use of southern blot hybridization of ClaI genomic digests with mecA and Tn554 allowed us a significant increase in discrimination, differentiating at least 32 different clones. Two major clones, however, each sharing common ClaI-mecA and Tn554 type and PFGE pattern as well as a common resistance phenotype, represented more than 50% of all MRSA isolates. The recovery of these two clones in the majority of the isolates of adult and neonatal intensive care units, respectively, is indicative of typical nosocomial outbreaks and clonal spread. It is concluded that intensive care units are major areas requiring preventative interventions.     

苏州市154株金黄色葡萄球菌耐药监测及脉冲场凝胶电泳分型

目的 分析苏州市2014 - 2017年金黄色葡萄球菌（staphylococcus aureus, SAU）的耐药情况和耐甲氧西林金黄色葡萄球菌（methicillin - resistance staphylococcus aureus,MRSA）的脉冲场凝胶电泳（pulsed - field gel electrophoresis, PFGE）分型特征,为临床合理使用抗生素提供参考,为MRSA感染溯源提供技术支持。方法 主要采用MIC法对常见的19种抗生素进行药敏试验,对检测为MRSA的菌株进行PFGE分析。结果 SAU耐药率达到93.5%,未发现万古霉素、达托霉素、奎奴普汀/达福普丁和利奈唑胺的耐药菌株。MRSA多重耐药率达到96.2%。MRSA对多种抗生素的耐药率明显高于甲氧西林敏感金黄色葡萄球菌,且差异具有统计学意义（P＜0.05）。26株MRSA共有15个PFGE型别,有3株100%同源的菌株来自同一所医院3位不同病人。结论 苏州市SAU除对万古霉素、达托霉素、奎奴普汀/达福普丁和利奈唑胺敏感外,对其他抗生素均发现耐药现象,MRSA多重耐药率较高。因此,应用抗生素治疗时建议进行药敏试验。MRSA的PFGE基因型别呈现分布多样性,存在院内传播的可能性,应加强PFGE在溯源分析中的应用。     

Antimicrobial use and methicillin-resistant Staphylococcus aureus in a large nursing home

INTRODUCTION: In 1997, 18% of Staphylococcus aureus clinical isolates at the Wisconsin Veterans Home were resistant to methicillin. By 2002, 51% were resistant. METHODS: We determined the antibiotic sensitivity pattern of our methicillin-resistant S. aureus (MRSA) isolates as well as changes in utilization of specific antibiotics between two time periods. We reasoned that antibiotics with activity against methicillin-sensitive S. aureus (MSSA), but not MRSA, might be driving the overgrowth of MRSA. RESULTS: In our facility, MRSA is usually resistant to quinolones; MSSA is usually sensitive. Both MSSA and MRSA are usually sensitive to TMP-sulfa. An increased percentage of S. aureus resistant to methicillin (18%) was associated with a 42% increase in quinolone use and a 37% decrease in TMP-sulfa use. CONCLUSION: Our analysis and previous reports suggest that replacement of TMP-sulfa by quinolones could be selecting MRSA in our facility. This conclusion, however, is speculative, based on association, and requires confirmation.     

Costs and outcomes among hemodialysis-dependent patients with methicillin-resistant or methicillin-susceptible Staphylococcus aureus bacteremia.

OBJECTIVE: Comorbid conditions have complicated previous analyses of the consequences of methicillin resistance for costs and outcomes of Staphylococcus aureus bacteremia. We compared costs and outcomes of methicillin resistance in patients with S. aureus bacteremia and a single chronic condition. DESIGN, SETTING, AND PATIENTS: We conducted a prospective cohort study of hemodialysis-dependent patients with end-stage renal disease and S. aureus bacteremia hospitalized between July 1996 and August 2001. We used propensity scores to reduce bias when comparing patients with methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) S. aureus bacteremia. Outcome measures were resource use, direct medical costs, and clinical outcomes at 12 weeks after initial hospitalization. RESULTS: Fifty-four patients (37.8%) had MRSA and 89 patients (62.2%) had MSSA. Compared with patients with MSSA bacteremia, patients with MRSA bacteremia were more likely to have acquired the infection while hospitalized for another condition (27.8% vs 12.4%; P = .02). To attribute all inpatient costs to S. aureus bacteremia, we limited the analysis to 105 patients admitted for suspected S. aureus bacteremia from a community setting. Adjusted costs were higher for MRSA bacteremia for the initial hospitalization (21,251 dollars vs 13,978 dollars; P = .012) and after 12 weeks (25,518 dollars vs 17,354 dollars; P = .015). At 12 weeks, patients with MRSA bacteremia were more likely to die (adjusted odds ratio, 5.4; 95% confidence interval, 1.5 to 18.7) than were patients with MSSA bacteremia. CONCLUSIONS: Community-dwelling, hemodialysis-dependent patients hospitalized with MRSA bacteremia face a higher mortality risk, longer hospital stays, and higher inpatient costs than do patients with MSSA bacteremia.     

Enterotoxin and toxic shock syndrome toxin-1 production of methicillin resistant and methicillin sensitive Staphylococcus aureus strains

In this study the production of enterotoxin A-D and toxic shock syndrome toxin-1 (TSST-1) of 181 methicillin resistant (MRSA) and 100 methicillin sensitive (MSSA) Staphylococcus aureus first isolates from different patients was investigated. All the MRSA- and MSSA isolates in the study were collected in a period between 1993 and 1995 from specimens sent from 11 different acute care hospitals in the greater Düsseldorf area. As far as possible the isolates were matched according to ward and hospital. The isolates were collected in the same time period and matched for specimen from which isolated. Furthermore, only first isolates were analysed in both groups. No significant difference in the production of toxin of any type between MRSA and MSSA could be detected (51 and 40% respectively). When the individual toxins were analysed, again no significant difference between MRSA and MSSA was demonstrable (enterotoxin production by MRSA 40% and MSSA 36%, and TSST-1 16% and 8% respectively). Despite this, a slight tendency for MRSA to produce enterotoxin A and B and for MSSA to produce enterotoxin C was observed. In addition, generation of TSST-1 by both groups was independent of enterotoxin A-D production. Interestingly, no increase in the proportion of TSST-1- or enterotoxin-producing MRSA and MSSA isolates was observed in strains isolated from blood cultures from patients with a clinical diagnosis of sepsis. Genotypical pulsed-field-gel-electrophoresis (PFGE) and phenotypical (bacteriophage typing, lysotyping) characterization of the 181 MRSA isolates resulted in 28 different PFGE patterns (of which 19 were toxin producers) and 22 lysotyping groups (18 of which produced toxin). In summary, the investigated clinical S. aureus isolates showed no difference in their ability to produce toxin and this was independent of their sensitivity to methicillin.     

Comparison of mortality risk associated with bacteremia due to methicillin-resistant and methicillin-susceptible Staphylococcus aureus.

OBJECTIVE: To quantify the clinical impact of methicillin-resistance in Staphylococcus aureus causing infection complicated by bacteremia in adult patients, while controlling for the severity of patients' underlying illnesses. DESIGN: Retrospective cohort study from October 1, 1995, through December 31, 2003. PATIENTS AND SETTING: A total of 438 patients with S. aureus infection complicated by bacteremia from a single Veterans Affairs healthcare system. RESULTS: We found that 193 (44%) of the 438 patients had methicillin-resistant S. aureus (MRSA) infection and 114 (26%) died of causes attributable to S. aureus infection within 90 days after the infection was identified. Patients with MRSA infection had a higher mortality risk, compared with patients with methicillin-susceptible S. aureus (MSSA) infections (relative risk, 1.7 [95% confidence interval, 1.3-2.4]; P<.01), except for patients with pneumonia (relative risk, 0.7 [95% confidence interval, 0.4-1.3]). Patients with MRSA infections were significantly older (P<.01), had more underlying diseases (P=.02), and were more likely to have severe sepsis in response to their infection (P<.01) compared with patients with MSSA bacteremia. Patients who died within 90 days after S. aureus infection was identified were significantly older (P<.01) and more likely to have severe sepsis (P<.01) and pneumonia (P=.01), compared with patients who survived. After adjusting for age as a confounder, comorbidities, and pneumonia as an effect modifier, S. aureus infection-related mortality remained significantly higher in patients with MRSA infection than in those with MSSA infection, among those without pneumonia (hazard ratio, 1.8 [95% confidence interval, 1.2-3.0]); P<.01. CONCLUSIONS: The results of this study suggest that patients with MRSA infections other than pneumonia have a higher mortality risk than patients with MSSA infections other than pneumonia, independent of the severity of patients' underlying illnesses.     

Importance of control group selection for evaluating antimicrobial use as a risk factor for methicillin-resistant Staphylococcus aureus bacteremia.

OBJECTIVE: We investigated the importance of control group selection during an evaluation of antimicrobial use as a risk factor for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia at our institution. METHODS: We performed a case-control study. A case was defined as any patient admitted between January 1997 and May 2001 who developed nosocomial MRSA bacteremia. We used two control groups; control group I consisted of patients with nosocomial methicillin-susceptible S. aureus (MSSA) bacteremia and control group II included only patients without bacteremia. We matched control-patients to case-patients using age, gender, time at risk, and hospital ward. Data collected on all patients included demographics, comorbidities, antibiotic use, time at risk, length of stay, severity of illness, and outcome. RESULTS: We evaluated 63 patients (21 in each group). The three groups were well matched regarding age, gender, underlying diseases, and severity of illness. Patients in the MRSA group were more likely to have received a fluoroquinolone and had a higher mean number of days of fluoroquinolone use than did patients in the MSSA group (P = .027 and P = .015, respectively). However, all measures of fluoroquinolone use were similar for case-patients and for control-patients who did not have nosocomial bloodstream infection. CONCLUSIONS: Control group selection is important in evaluating antimicrobial use as a risk factor for MRSA bacteremia. Using control-patients infected with MSSA, rather than uninfected control-patients, may overestimate the association between antimicrobial use and MRSA infection.     

Frequency and diversity of molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) isolates from patients of a South West German teaching hospital

We have determined the frequency and the genetic diversity of methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from inpatients of a South West German teaching hospital. The frequency of primary MRSA isolates remained constant over the two-year surveillance period: 108 of the total number of 1450 S. aureus isolates (7.5%) were MRSA in 2001 and the corresponding figures were 110 MRSA out of 1412 S. aureus isolates (7.8%) in 2002. Six clusters of nosocomial MRSA infection were observed during 2001 and 2002. Cluster infections involved 65 patients on four different wards. Molecular typing of the 65 cluster isolates demonstrated that 51 (79%) belonged to a single predominant clone. The remaining 14 isolates represented seven genetically unrelated MRSA clones. Molecular typing of 50 additional non-cluster, sporadic isolates demonstrated 37 different pulsed-field gel electrophoresis (PFGE) banding patterns. Our results demonstrate that primary MRSA strains from hospitalized patients show a high degree of genetic heterogeneity. In contrast, however, MRSA isolates from nosocomial clusters were mostly derived from a single predominant clone, thus indicating a significant intra-ward and intra-hospital distribution. Molecular typing methods may lead to an improved understanding of MRSA epidemiology and thus allow the establishment of effective preventive measures.     

Coagulase gemne variants associated with distinct populations of Staphylococcus aureus

An identifying characteristic of Staphylococcus aureus is the production of staphylocoagulase (coagulase). The aim of this study was to determine the clonal distribution of coagulase gene (coa) variants within populations of S. aureus defined by multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE), and protein A variation. The N-terminal region of the coa gene from 43 methicillin-susceptible (MSSA) and 252 methicillin-resistant (MRSA) S. aureus human isolates and 9 animal S. aureus isolates was amplified and digested with HinfI. Twelve types were identified amongst the MSSA isolates and the majority (93%) of MRSA isolates were assigned to 5 of the 12 types. MLST and PFGE analysis identified epidemic populations of MRSA and each epidemic population was characterized by a different coagulase type. Nine of the 12 MLST-defined clonal complex ancestral genotypes recently described each carried a different coagulase type suggesting that coagulase evolution and the evolution of the clonal complexes are intimately related.     

Frequent acquisition of multiple strains of methicillin-resistant Staphylococcus aureus by healthcare workers in an endemic hospital environment

Methicillin-resistant Staphylococcus aureus (MRSA) has been an endemic nosocomial pathogen at the VA medical center (VAMC) in Providence, Rhode Island since 1981. From 1985 to 1987, more than 30% of all unique S aureus isolates were methicillin resistant. To evaluate the frequency of acquisition of MRSA isolates by healthcare workers, we compared the antimicrobial susceptibility patterns, multilocus enzyme genotypes and plasmid profiles of isolates recovered from nasal and hand cultures from VAMC nurses and house staff on rotation at the VAMC with those of clinical isolates from patients at the VAMC and four other affiliated hospitals. Fifty-six percent of ward nurses cultured (n = 112) were colonized with S aureus, of which 65% was methicillin resistant. Six isolates of MRSA were identified on the initial culturing of house staff (n = 65); 16 MRSA isolates were recovered at the end of a four-week rotation (p less than .02). Phenotypic and genotypic analyses demonstrated that numerous distinct MRSA strains were recovered in the study period. The incidence of MRSA among clinical isolates at the VAMC and affiliated institutions was remarkably constant throughout the three-year study period. Moreover, despite regularly sharing resident physicians, interns and medical students, MRSA isolates were commonly recovered at the other university-affiliated hospitals. Our study failed to reveal evidence of significant interhospital transmission of MRSA isolates by healthcare workers. While healthcare workers may contribute to the dissemination of MRSA within institutions, they appear to be less important in spreading MRSA between institutions.     

金黄色葡萄球菌临床分离株耐药谱分析

目的调查2005年1~8月分离自江西宜春金黄色葡萄球菌的耐药情况。方法采用常规方法分离金黄色葡萄球菌,用全自动微生物分析仪进行菌种鉴定和药敏试验,采用苯唑西林纸片扩散法检测耐甲氧西林金黄色葡萄球菌(MRSA)。结果金黄色葡萄球菌主要分离自痰液和尿液,MRSA的分离率为62.1%;MRSA对氨苄西林/舒巴坦、青霉素和头孢唑林的耐药率均为100%,而MSSA均为0;所有的分离株对呋喃妥因和万古霉素都敏感;MRSA对克林霉素、红霉素、庆大霉素、四环素、利福平、复方新诺明和左氧氟沙星的耐药率分别为70.7%、86.6%、87.8%、82.9%、42.7%、30.5%和91.5%,而MSSA分别为32.0%、42.0%、20.0%、20.0%、10.0%、30.0%和6.0%。结论MRSA的耐药性较为严重,而MSSA除青霉素外耐药率较低,万古霉素对MRSA的体外抗菌活性非常强。     

Healthcare-associated Staphylococcus aureus bacteremia and the risk for methicillin resistance: is the Centers for Disease Control and Prevention definition for community-acquired bacteremia still appropriate?

OBJECTIVE: To evaluate a new classification for bloodstream infections that differentiates hospital acquired, healthcare associated, and community acquired in patients with blood cultures positive for Staphylococcus aureus. DESIGN: Prospective, observational study. SETTING: Three tertiary-care, university-affiliated hospitals in Dublin, Ireland, and Strasbourg, France. PATIENTS: Two hundred thirty consecutive patients older than 18 years with blood cultures positive for S. aureus. METHODS: S. aureus bacteremia (SAB) was defined as hospital acquired if the first positive blood culture was performed more than 48 hours after admission. Other SABs were classified as healthcare associated or community acquired according to the definition proposed by Friedman et al. When available, strains of methicillin-resistant Staphylococcus aureus (MRSA) were analyzed by pulsed-field gel electrophoresis (PFGE). RESULTS: Eighty-two patients were considered as having community-acquired bacteremia according to the Centers for Disease Control and Prevention (CDC) classification. Of these 82 patients, 56% (46) had healthcare-associated SAB. MRSA prevalence was similar in patients with hospital-acquired and healthcare-associated SAB (41% vs 33%; P > .05), but significantly lower in the group with community-acquired SAB (11%; P < .03). PFGE of MRSA strains showed that most community-acquired and healthcare-associated MRSA strains were similar to hospital-acquired MRSA strains. On multivariate analysis, Friedman's classification was more effective than the CDC classification for predicting MRSA. CONCLUSION: These results support the call for a new classification for community-acquired bacteremia that would account for healthcare received outside the hospital by patients with SAB.     

Antimicrobial resistance in Staphylococcus aureus at the University of Chicago Hospitals: a 15-year longitudinal assessment in a large university-based hospital.

OBJECTIVES: To describe a longitudinal profile of resistance to beta-lactam antimicrobials among isolates of Staphylococcus aureus at a large university teaching hospital and to evaluate the impact of the methicillin resistance phenotype on resistance trends for non-beta-lactam antimicrobials. DESIGN: Retrospective evaluation of antimicrobial susceptibility data for all 17,287 S. aureus isolates obtained from January 1986 through December 2000. SETTING: The University of Chicago Hospitals, a family of tertiary-care, university-affiliated hospitals in Chicago, Illinois, consisting of 547 adult and pediatric beds. RESULTS: The annual rate of resistance to methicillin increased from 13% in 1986 to 28% in 2000 (P < .001) and has not plateaued. For each non-beta-lactam antimicrobial tested, the annual rates of resistance were far higher among methicillin-resistant S. aureus (MRSA) isolates than among methicillin-susceptible S. aureus (MSSA) isolates. The annual rates of resistance to the macrolide, lincosamide, and streptogramin (MLS) antimicrobials erythromycin and clindamycin increased among MSSA isolates (P < .01), but remained lower than 20%. Resistance to the MLS antimicrobials was higher among MRSA isolates (higher than 60%), but the annual rate decreased significantly during the study (P < .01). CONCLUSION: The prevalence of methicillin resistance among S. aureus isolates has continued to increase; resistance to non-beta-lactam antimicrobials is far more common among MRSA isolates. Recent decreases in the proportion of MRSA isolates resistant to non-beta-lactam antimicrobials suggest important changes in the epidemiology of this pathogen.     

Prevalence of community-acquired methicillin-resistant Staphylococcus aureus colonization in a random sample of healthy individuals.

BACKGROUND: Concern has recently arisen that the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization among populations at low risk for acquiring this pathogen has been increasing. Although previous studies have reported on the prevalence of MRSA colonization, most of these studies have been performed in healthcare settings, with few studies performed in the community among healthy individuals in non-healthcare locations. OBJECTIVES: To determine the prevalence of community-acquired (CA) MRSA colonization in a random sample of healthy individuals in 4 non-healthcare locations and to compare the genetic similarity between these CA isolates and nosocomial MRSA isolates. DESIGN: Prospective, observational study conducted from October 2004 through February 2005. SETTING: Two colleges, 1 church, and 1 restaurant in Newark and Wilmington, Delaware. PARTICIPANTS: A total of 295 healthy volunteers. RESULTS: The rate of S. aureus colonization was 26.8%. Of the 79 S. aureus isolates analyzed, 3 (4%) were resistant to methicillin. Ribotyping of the 3 MRSA isolates showed that they were genetically distinct from each other. Each of the 3 CA isolates were genetically indistinguishable from 3 different nondominant clusters of MRSA isolates found in the medical and surgical intensive care units of Christiana Care Health System (Newark) and Wilmington Hospital (Wilmington). CONCLUSION: The overall prevalence of CA-MRSA colonization in a random sample of healthy individuals in 4 non-healthcare locations in Newark and Wilmington was 1.0%. Despite concerns that the prevalence of MRSA colonization is increasing, it still remains relatively low in our community, perhaps because CA-MRSA colonization tends to occur in clusters.     

Nosocomial methicillin-resistant and methicillin-susceptible Staphylococcus aureus primary bacteremia: at what costs?

OBJECTIVE: To determine the attributable hospital stay and costs for nosocomial methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) primary bloodstream infections (BSIs). DESIGN: Pairwise-matched (1:1) nested case-control study. SETTING: University-based tertiary-care medical center. PATIENTS: Patients admitted between December 1993 and March 1995 were eligible. Cases were defined as patients with a primary nosocomial S. aureus BSI; controls were selected according to a priori matching criteria. MEASUREMENTS: Length of hospital stay and total and variable direct costs of hospitalization. RESULTS: The median hospital stay attributable to primary nosocomial MSSA BSI was 4 days, compared with 12 days for MRSA (P=.023). Attributable median total cost for MSSA primary nosocomial BSIs was $9,661 versus $27,083 for MRSA nosocomial infections (P=.043). CONCLUSION: Nosocomial primary BSI due to S. aureus significantly prolongs the hospital stay. Primary nosocomial BSIs due to MRSA result in an approximate threefold increase in direct cost, compared with those due to MSSA.