Methicillin-Resistant Staphylococcus aureus Carriage and Risk Factors for Skin Infections, Southwestern Alaska, USA

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are common in southwestern Alaska. Outbreak strains have been shown to carry the genes for Panton-Valentine leukocidin (PVL). To determine if carriage of PVL-positive CA-MRSA increased the risk for subsequent soft tissue infection, we conducted a retrospective cohort study by reviewing the medical records of 316 persons for 3.6 years after their participation in a MRSA nasal colonization survey. Demographic, nasal carriage, and antimicrobial drug use data were analyzed for association with skin infection risk. Skin infections were more likely to develop in MRSA carriers than in methicillin-susceptible S. aureus carriers or noncarriers of S. aureus during the first follow-up year, but not in subsequent years. Repeated skin infections were more common among MRSA carriers. In an area where PVL-containing MRSA is prevalent, skin infection risk was increased among MRSA nasal carriers compared with methicillin-susceptible S. aureus carriers and noncarriers, but risk differential diminished over time.     

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.     

Staphylococcus aureus infections in US veterans, Maryland, USA, 1999-2008

Trends in Staphylococcus aureus infections are not well described. To calculate incidence in overall S. aureus infection and invasive and noninvasive infections according to methicillin susceptibility and location, we conducted a 10-year population-based retrospective cohort study (1999-2008) using patient-level data in the Veterans Affairs Maryland Health Care System. We found 3,674 S. aureus infections: 2,816 (77%) were noninvasive; 2,256 (61%) were methicillin-resistant S. aureus (MRSA); 2,517 (69%) were community onset, and 1,157 (31%) were hospital onset. Sixty-one percent of noninvasive infections were skin and soft tissue infections; 1,112 (65%) of these were MRSA. Ten-year averaged incidence per 100,000 veterans was 749 (± 132 SD, range 549-954) overall, 178 (± 41 SD, range 114-259) invasive, and 571 (± 152 SD, range 364-801) noninvasive S. aureus infections. Incidence of all S. aureus infections significantly increased (p<0.001), driven by noninvasive, MRSA, and community-onset infections (p<0.001); incidence of invasive S. aureus infection significantly decreased (p<0.001).     

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.     

Methicillin-resistant Staphylococcus aureus bacteraemia in Hong Kong

In the first 22 months of operation at the Prince of Wales Hospital, 26 (46%) of 56 hospital-acquired Staphylococcus aureus bacteraemias were due to methicillin-resistant organisms (MRSA). There were 10 plasmid profiles amongst 24 of the MRSA strains analysed. MRSA bacteraemias were first seen in the hospital 1 year after opening when the isolation rate of MRSA from all sites had risen to about 1% of patient admissions. During the last 3 months of the study period, 17 out of 18 S. aureus bacteraemias were due to methicillin-resistant strains. Patients with MRSA bacteraemia were significantly more likely than those with methicillin-sensitive S. aureus bacteraemia to have had a severe underlying disease, a poor clinical prognosis, prolonged hospitalization, and prior antimicrobial therapy, especially with aminoglycosides. They also had a significantly longer hospital stay after infection, a significantly higher cost of antimicrobial therapy and a higher mortality rate. The lower mortality rate in MRSA patients treated with vancomycin (18%) compared with those treated with other antimicrobials (40%) confirms that, at present, vancomycin is the treatment of choice for invasive MRSA infections.     

Epidemiology and clonality of methicillin-resistant and methicillin-susceptible Staphylococcus aureus causing bacteremia in a tertiary-care hospital in Spain.

OBJECTIVES: To describe the relative proportions of nosocomial and community-onset Staphylococcus aureus bacteremia at our institution and the epidemiologic characteristics and clonal diversity of S. aureus isolates, as determined by pulsed-field gel electrophoresis (PFGE) and antimicrobial resistance patterns. DESIGN: Retrospective cohort study of all cases of S. aureus bacteremia between October 2001 and October 2002. SETTING: A 1300-bed, tertiary-care hospital. RESULTS: One hundred sixty-two unique episodes of S. aureus bacteremia were identified. Forty-three cases (26.5%) were caused by methicillin-resistant S. aureus (MRSA). Most cases of S. aureus bacteremia, whether MRSA or methicillin susceptible (MSSA), were nosocomial in origin (77.2%) or were otherwise associated with the healthcare system (16%). Only 11 (6.8%) of the cases (all MSSA) were strictly community acquired. Thirty-five unique macrorestriction patterns were identified among the 154 isolates that were typed by PFGE. Four major genotypes were defined among the isolates of MRSA, with 36 (85.7%) represented by a single PFGE type. Of the isolates within this major clone, all (100%) were ciprofloxacin resistant and 77.8% were erythromycin resistant. In contrast, the 112 isolates of MSSA comprised 31 different PFGE types, 3 of which represented 42.9% of all MSSA isolates and were associated with both nosocomial and community-onset bacteremia. CONCLUSIONS: Most cases of S. aureus bacteremia in our healthcare region are nosocomial in origin or are acquired through contact with the healthcare system and are thus potentially preventable. To preclude dissemination of pathogenic clones, it is therefore necessary to redouble preventive measures in both the hospital and the community.     

Methicillin-resistant-Staphylococcus aureus hospitalizations, United States

Methicillin-resistant Staphylococcus aureus (MRSA) is increasingly a cause of nosocomial and community-onset infection with unknown national scope and magnitude. We used the National Hospital Discharge Survey to calculate the number of US hospital discharges listing S. aureus-specific diagnoses, defined as those having at least 1 International Classification of Diseases (ICD)-9 code specific for S. aureus infection. The number of hospital discharges listing S. aureus-specific diagnoses was multiplied by the proportion of methicillin resistance for each corresponding infection site to determine the number of MRSA infections. From 1999 to 2000, an estimated 125,969 hospitalizations with a diagnosis of MRSA infection occurred annually, including 31,440 for septicemia, 29,823 for pneumonia, and 64,706 for other infections, accounting for 3.95 per 1,000 hospital discharges. The method used in our analysis may provide a simple way to assess trends of the magnitude of MRSA infection nationally.     

Staphylococcus aureus bacteremia, Australia

Staphylococcus aureus bacteremia (SAB) is common and increasing worldwide. A retrospective review was undertaken to quantify the number of cases, their place of acquisition, and the proportions caused by methicillin-resistant S. aureus (MRSA) in 17 hospitals in Australia. Of 3,192 episodes, 1,571 (49%) were community onset. MRSA caused 40% of hospital-onset episodes and 12% of community-onset episodes. The median rate of SAB was 1.48/1,000 admissions (range 0.61-3.24; median rate for hospital-onset SAB was 0.7/1,000 and for community onset 0.8/1,000 admissions). Using these rates, we estimate that approximately 6,900 episodes of SAB occur annually in Australia (35/100,000 population). SAB is common, and a substantial proportion of cases may be preventable. The epidemiology is evolving, with >10% of community-onset SAB now caused by MRSA. This is an emerging infectious disease concern and is likely to impact on empiric antimicrobial drug prescribing in suspected cases of SAB.     

Staphylococcus aureus bacteraemia: incidence, risk factors and predictors for death in a Brazilian teaching hospital

The aim of this study was to evaluate the incidence of bloodstream infection due to Staphylococcus aureus and the risk factors for mortality. The design was a two-year retrospective cohort of patients more than one year of age with clinically significant and microbiologically documented bloodstream infection due to S. aureus between January 2000 and December 2001 in a tertiary teaching hospital in midwest Brazil. One hundred and eleven patients were identified with clinically significant and microbiologically confirmed bacteraemia due to S. aureus, accounting for an infection rate of five per 1000 admissions. Nosocomial infections represented 83.8% of cases and meticillin-resistant Staphylococcus aureus (MRSA) accounted for 60.2% of cases. Overall mortality due to S. aureus bacteraemia was 35.1%. Infection due to MRSA, severity of clinical status (severe sepsis or septic shock) and inadequate initial antimicrobial therapy were identified by univariate analysis as predictors of mortality. After Cox regression analysis, severity of clinical manifestations [hazard ratio (HR) 6.86, 95% confidence interval (CI) 3.05-15.43] and inadequacy of antimicrobial therapy (HR 2.27, 95%CI 1.02-5.09) remained as risk factors for mortality. Early diagnosis of bacteraemia should be sought in order to implement adequate treatment before the onset of severe sepsis and septic shock, thus reducing the mortality rate.     

Community-acquired methicillin-resistant Staphylococcus aureus in Central Australia

To date, there has been scant information about the burden of methicillin-resistant Staphylococcus aureus infections in Central Australia. Our aims were to determine the proportion of Staphylococcus aureus infections due to methicillin-resistant strains in Central Australia, to characterise resistance to non-beta lactam antibiotics and to correlate findings with available demographic information. We retrospectively reviewed S. aureus isolates identified by the Microbiology Laboratory of the Pathology Department, Alice Springs Hospital between September 2005 and February 2006. Multi-resistance was defined as resistance to three or more non-beta lactam antibiotics. We identified the recovery site and extended antibiotic resistance profile of each isolate. Demographic data included place of residence, discharge diagnosis and ethnicity. There were 524 S. aureus isolates: 417 (79.6%) methicillin-sensitive S. aureus, 104 (19.7%) non-multi-resistant MRSA (nmrMRSA) and 3 (0.7%) multi-resistant MRSA (mrMRSA). MRSA accounted for 7/22 (32%) invasive infections and 91/474 (19.2%) cases of staphylococcal skin infections. Aboriginal people comprised 89 per cent (93/104) of patients with nmrMRSA; 57 per cent lived in remote communities, 21 per cent in suburban Alice Springs, and 18 per cent in Alice Springs Town Camps. Six per cent (6/104) of nmrMRSA were hospital-acquired. Of the nmrMRSA isolates, 57 per cent (59/104) were resistant to erythromycin and 7 per cent (7/104) to fusidic acid. All MRSA isolates were susceptible to co-trimoxazole. In conclusion, Central Australia has high rates of community-acquired nmrMRSA and low rates of multi-resistant MRSA. Erythromycin resistance in S. aureus is also common. These findings should prompt the review of antimicrobial prescribing guidelines for the region, especially for treatment of skin and soft tissue infections.     

Invasive methicillin-resistant Staphylococcus aureus infections among dialysis patients--United States, 2005

Staphylococcus aureus is a leading cause of bloodstream and other invasive infections in the United States. S. aureus has become increasingly resistant to first-line antimicrobial agents in health-care settings. Dialysis patients are especially vulnerable to infections, frequently those caused by antimicrobial-resistant organisms, including methicillin-resistant Staphylococcus aureus (MRSA). To assess the incidence of invasive MRSA infection among dialysis patients in the United States during 2005, surveillance data were analyzed from the Active Bacterial Core surveillance (ABCs) system. This report summarizes the results of that analysis, which estimated that, in 2005, the incidence of invasive MRSA infection among dialysis patients was 45.2 cases per 1,000 population. Persons receiving dialysis are at high risk for infection with invasive MRSA compared with the general population, in which rates of invasive MRSA have ranged from 0.2 to 0.4 infections per 1,000 population. The findings in this report underscore the need for continued surveillance and infection-control strategies aimed at reducing infection rates and preventing additional antimicrobial resistance among persons receiving dialysis.     

Molecular epidemiology of methicillin-resistant Staphylococcus aureus, rural southwestern Alaska

USA300 is the dominant strain responsible for community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) infections in most of the United States. We examined isolates from outbreaks of MRSA skin infections in rural southwestern Alaska in 1996 and 2000 (retrospective collection) and from the hospital serving this region in 2004-2006 (prospective collection). Among 36 retrospective collection isolates, 92% carried Panton-Valentine leukocidin (PVL) genes; all carried staphylococcal chromosomal cassette mec (SCCmec) type IV. None belonged to clonal complex (CC) 8, the CC associated with USA300; 57% were sequence type (ST) 1, and 26% were ST30; 61% were clindamycin resistant. In the prospective collection, 42 isolates were PVL+ and carried SCCmec type IV; 83.3% were ST1, 9.5% were ST30, and 7.1% were ST8. Among 120 prospective isolates, 57.5% were clindamycin resistant. CA-MRSA epidemiology in southwestern Alaska differs from that in the lower 48 states; ST8 strains were rarely identified and clindamycin resistance was common.     

Fluoroquinolones and risk for methicillin-resistant Staphylococcus aureus, Canada

Receipt of fluoroquinolones was the predominant risk factor for Clostridium difficile-associated disease (CDAD) during an epidemic in Quebec, Canada. To determine the role of antimicrobial drugs in facilitating healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) colonization and infection and to compare this role with their effects on methicillin-susceptible S. aureus infection and CDAD, we conducted a retrospective cohort study of patients in a Quebec hospital. For 7371 episodes of care, data were collected on risk factors, including receipt of antimicrobial drugs. Crude and adjusted hazard ratios (AHR) were calculated by Cox regression. Of 150 episodes of MRSA colonization and 23 of MRSA infection, fluoroquinolones were the only antimicrobials that increased risk for colonization (AHR 2.57, 95% confidence interval [CI] 1.84-3.60) and infection (AHR 2.49, 95% CI 1.02-6.07). Effect of antimicrobial drugs on MRSA colonization and infection was similar to effect on CDAD and should be considered when selecting antimicrobial drugs to treat common infections.     

金黄色葡萄球菌感染的特征及其耐药性

目的探索金黄色葡萄球菌感染的特征及其耐药性,预防和控制MRSA流行发生。方法对2006年住院患者中金黄色葡萄球菌感染的特征及耐药性进行监测。结果2006年共分离出金黄色葡萄球菌45株,其中MRSA28株,占金葡菌的62.2%(MSSA17株,占37.8%);医院感染株和社区感染株分别占19株(42.2%)、26株(57.8%);感染部位多分布在下呼吸道、皮肤软组织和烧伤部位;在同期空气、物体表面、医务人员手等外环境中尚未检出金黄色葡萄球菌。金葡菌对阿莫西林、氨苄西林、青霉素G、阿奇霉素耐药率在70%以上,但对万古霉素敏感。基础疾病中以外伤、心脑血管病、烧伤、呼吸系统疾病、皮肤软组织疾病居前五位。结论金葡菌检出率、MRSA发生率和耐药率较高;同期外环境尚未发现有关的金葡菌菌株;金葡菌医院感染以内源性感染为主;应注意做好手卫生、物体表面消毒和合理使用抗菌药物,预防控制金葡菌交叉传播。     

Colonization with methicillin-resistant Staphylococcus aureus in ICU patients: morbidity, mortality, and glycopeptide use.

OBJECTIVE: To determine the impact of methicillin-resistant Staphylococcus aureus (MRSA) colonization on the occurrence of S. aureus infections (methicillin-resistant and methicillin-susceptible), the use of glycopeptides, and outcome among intensive care unit (CU) patients. DESIGN: Prospective observational cohort survey. SETTING: A medical-surgical ICU with 10 single-bed rooms in a 460-bed, tertiary-care, university-affiliated hospital. PATIENTS: A total of 1,044 ICU patients were followed for the detection of MRSA colonization from July 1, 1995, to July, 1 1998. METHODS: MRSA colonization was detected using nasal samples in all patients plus wound samples in surgical patients within 48 hours of admission or within the first 48 hours of ICU stay and weekly thereafter. MRSA infections were defined using Centers for Disease Control and Prevention standard definitions, except for ventilator-associated pneumonia and catheter-related infections, which were defined by quantitative distal culture samples. RESULTS: One thousand forty-four patients (70% medical patients) were included in the analysis. Mean age was 61+/-18 years; mean Simplified Acute Physiologic Score (SAPS) II was 36.4+/-20; and median ICU stay was 4 (range, 1-193) days. Two hundred thirty-one patients (22%) died in the ICU. Fifty-four patients (5.1%) were colonized with MRSA on admission, and 52 (4.9%) of 1,044 acquired MRSA colonization in the ICU. Thirty-five patients developed a total of 42 S. aureus infections (32 MRSA, 10 methicillin-susceptible). After factors associated with the development of an S. aureus infection were adjusted for in a multivariate Cox model (SAPS II >36: hazard ratio [HR], 1.64; P=.09; male gender: HR, 2.2; P=.05), MRSA colonization increased the risk of S. aureus infection (HR, 3.84; P=.0003). MRSA colonization did not influence ICU mortality (HR, 1.01; P=.94). Glycopeptides were used in 11.4% of the patients (119/1,044) for a median duration of 5 days. For patients with no colonization, MRSA colonization on admission, and ICU-acquired MRSA colonization, respectively, glycopeptide use per 1,000 hospital days was 37.7, 235.2, and 118.3 days. MRSA colonization per se increased by 3.3-fold the use of glycopeptides in MRSA-colonized patients, even when an MRSA infection was not demonstrated, compared to non-colonized patients. CONCLUSIONS: In our unit, MRSA colonization greatly increased the risk of S. aureus infection and of glycopeptide use in colonized and non-colonized patients, without influencing ICU mortality. MRSA colonization influenced glycopeptide use even if an MRSA infection was not demonstrated; thus, an MRSA control program is warranted to decrease vancomycin use and to limit glycopeptide resistance in gram-positive cocci.     

Community-associated methicillin-resistant Staphylococcus aureus infections in Pacific Islanders--Hawaii, 2001-2003

Methicillin-resistant Staphylococcus aureus (MRSA) is emerging as a cause of skin and soft-tissue infections in persons who have little or no contact with health-care settings. The majority of these infections are mild, involving skin and soft tissue; however, certain cases can progress to invasive tissue infections, bacteremia, and death. Transmission of MRSA has been reported most frequently in certain populations (e.g., children, sports participants, or jail inmates). Persons in the American Indian or Alaska Native population in the United States and aboriginals and Pacific Islanders (PIs) in Australia have high rates of MRSA colonization and infection. In 2003, clinicians reported an increased number of skin abscesses caused by MRSA among patients examined in ambulatory care settings. This report summarizes the findings of a retrospective study of community-associated MRSA (CA-MRSA) infections in Hawaii that identified a higher proportion of cases among PIs than were identified among Asians, compared with their respective proportions in the Hawaii population. Efforts to prevent CA-MRSA in Hawaii should focus on identifying factors causing the disproportionate number of infections among PIs.     

临床不同标本分离金黄色葡萄球菌的药物敏感性

目的了解某院金黄色葡萄球菌感染分布及药物敏感性。方法对2011年1月-2012年8月该院分离的520株金黄色葡萄球菌标本来源和药敏结果进行分析。结果520株金黄色葡萄球菌中,耐甲氧西林金黄色葡萄球菌（MRSA）总检出率为23.27%(121/520),其中痰标本MRSA检出率最高,达80.82%,其次是尿液（33.33%）、血液（25.00%）、引流物标本（18.31%）,皮肤组织检出率最低,仅11.38%。未发现对万古霉素和利奈唑胺耐药的金黄色葡萄球菌;金黄色葡萄球菌对万古霉素、利奈唑胺、复方磺胺甲口恶唑、呋喃妥因均较敏感。皮肤组织来源的MRSA对庆大霉素、左氧氟沙星、环丙沙星、莫西沙星、利福平、四环素的敏感率高于其他标本来源的MRSA（P＜0.05）;对红霉素、克林霉素敏感率低于其他标本来源MRSA（P＜0.05）。MRSA对青霉素完全耐药,其中社区感染MRSA对庆大霉素、左氧氟沙星、环丙沙星、莫西沙星、利福平、四环素的敏感率高于医院感染MRSA（P＜0.05）;对红霉素、克林霉素、复方磺胺甲口恶唑的敏感率低于医院感染MRSA（P＜0.05）。结论金黄色葡萄球菌是该院分离的重要病原菌,耐药性强,临床应根据药敏试验结果合理使用抗菌药物。     

皮肤感染耐甲氧西林金黄色葡萄球菌的分布及耐药性分析

目的 了解医院门诊及住院患者皮肤感染耐甲氧西林金黄色葡萄球菌(MRSA)的检出率及其耐药性,并分析耐药菌株对皮肤感染患者抗菌治疗的影响.方法 对2009-2011年皮肤感染金黄色葡萄球菌的400例患者进行回顾性分析,用黑马微生物分析系统进行细菌鉴定和药敏试验.结果 2009-2011年MRSA分别检出52、61、88株,检出率为45.2％、50.4％、53.7％,MRSA对青霉素的耐药率为100.0％,对红霉素、庆大霉素、磺胺甲噁唑/甲氧苄啶、左氧氟沙星、克林霉素和四环素的耐药率均＞50.0％;耐药率在10.0％～50.0％的抗菌药物为哌拉西林/舒巴坦、阿米卡星、头孢唑林、头孢曲松、头孢哌酮,对替考拉宁耐药率非常低,仅2.0％;未出现耐万古霉素菌株.结论 皮肤感染金黄色葡萄球菌对常用抗菌药物呈多药耐药状态,及时进行病原菌培养和药物敏感试验,根据药敏结果采取措施,是控制感染的关键.     

A comparison of clinical virulence of nosocomially acquired methicillin-resistant and methicillin-sensitive Staphylococcus aureus infections in a university hospital.

OBJECTIVES: To compare the clinical virulence of nosocomially acquired methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S aureus (MSSA) infections in 1989. DESIGN: A retrospective comparison of host factors, in-hospital exposures, sites of infections, and outcomes of patients with nosocomial MRSA and MSSA infections. SETTING: University of Illinois Hospital, Chicago, Illinois. PARTICIPANTS: Forty-four adult patients with nosocomial S aureus infections. RESULTS: 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. CONCLUSIONS: 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.     

Epidemiology of capsular and surface polysaccharide in Staphylococcus aureus infections complicated by bacteraemia

Staphylococcus aureus is a leading cause of serious hospital- and community-acquired infections. The discovery of serologically distinct capsular polysaccharides on the surface of clinical isolates has allowed the development of vaccines and passive protective immunity. We have studied patient characteristics, infection characteristics and the surface and capsular polysaccharide serotype distribution in patients with S. aureus infections complicated by bacteraemia admitted to VA hospitals in Maryland between 1995 and 2000. Nine hundred and ninety-three blood cultures from 331 patients were positive for S. aureus. Thirty-eight percent of patients had diabetes, 11% had end-stage renal failure, and 23% were injection drug users. Forty-two percent of infections were caused by methicillin-resistant strains (MRSA), and 60% were acquired during hospitalization. Serotyping of the first available isolate per patient (N=234 isolates) using polyclonal antibodies showed three major phenotypes--42%, type 8 (T8) capsule; 50%, type 5 (T5) capsule; and 8%, 336 polysaccharide. MRSA isolates were significantly more likely to be T5 than methicillin-susceptible isolates (66% vs. 39%, P<0.001). The proportion of T5 MRSA increased significantly (years 1-2: 41%; years 3-4: 65%; years 5-6: 90%, P<0.001). This large sample of patients with serious S. aureus infection confirms that capsular polysaccharides T5 and T8 cause most human infections, and together with serotype 336, account for nearly all those with bacteraemia.