Relationship between rates of antimicrobial consumption and the incidence of antimicrobial resistance in Staphylococcus aureus and Pseudomonas aeruginosa isolates from 47 French hospitals.

OBJECTIVE: To investigate relationships between rates of antimicrobial consumption and the incidence of antimicrobial resistance in Staphylococcus aureus and Pseudomonas aeruginosa isolates from hospitals. METHODS: We conducted an observational study that used retrospective data from 2002 and linear regression to model relationships. Hospitals were asked to collect data on consecutive S. aureus and P. aeruginosa isolates, consumption rates for antibiotics (ie, anti-infectives for systemic use as defined by Anatomical Therapeutic Chemical class J01), and hospital characteristics, including infection control policies. Rates of methicillin resistance in S. aureus and rates of ceftazidime and ciprofloxacin resistance in P. aeruginosa were expressed as the percentage of isolates that were nonsusceptible (ie, either resistant or intermediately susceptible) and as the incidence of nonsuceptible isolates (ie, the number of nonsuceptible isolates recovered per 1,000 patient-days). The rate of antimicrobial consumption was expressed as the number of defined daily doses per 1,000 patient-days. SETTING: Data were obtained from 47 French hospitals, and a total of 12,188 S. aureus isolates and 6,370 P. aeruginosa isolates were tested. RESULTS: In the multivariate analysis, fewer antimicrobials showed a significant association between the consumption rate and the percentage of isolates that were resistant than an association between the consumption rate and the incidence of resistance. The overall rate of antibiotic consumption, not including the antibiotics used to treat methicillin-resistant S. aureus infection, explained 13% of the variance between hospitals in the incidence of methicillin resistance among S. aureus isolates. The incidence of methicillin resistance in S. aureus isolates increased with the use of ciprofloxacin and levofloxacin and with the percentage of the hospital's beds located in intensive care units (adjusted multivariate coefficient of determination [aR(2)], 0.30). For P. aeruginosa, the incidence of ceftazidime resistance was greater in hospitals with higher consumption rates for ceftazidime, levofloxacin, and gentamicin (aR(2), 0.37). The incidence of ciprofloxacin resistance increased with the use of fluoroquinolones and with the percentage of a hospital's beds located in intensive care ( aR(2), 0.28). CONCLUSIONS: A statistically significant relationship existed between the rate of fluoroquinolone use and the rate of antimicrobial resistance among S. aureus and P. aeruginosa isolates. The incidence of resistant isolates showed a stronger association with the rate of antimicrobial use than did the percentage of isolates with resistance.     

Antimicrobial drug use and methicillin-resistant Staphylococcus aureus, Aberdeen, 1996-2000

Similar to many hospitals worldwide, Aberdeen Royal Infirmary has had an outbreak of methicillin-resistant Staphylococcus aureus (MRSA). In this setting, the outbreak is attributable to two major clones. The relationships between antimicrobial use and MRSA prevalence were analyzed by time-series analysis. From June 1997 to December 2000, dynamic, temporal relationships were found between monthly %MRSA and previous %MRSA, macrolide use, third-generation cephalosporin use, and fluoroquinolone use. This study suggests that use of antimicrobial drugs to which the MRSA outbreak strains are resistant may be an important factor in perpetuating the outbreak. Moreover, this study confirmed the ecologic effect of antimicrobial drug use (i.e., current antimicrobial use) may have an effect on resistance in future patients. Although these results may not be generalized to other hospitals, they suggest new directions for control of MRSA, which has thus far proved difficult and expensive.     

Methicillin-resistant Staphylococcus aureus bacteraemia in Western Australian teaching hospitals, 1997-1999: risk factors, outcomes and implications for management

The aim of this study was to document the evolution of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia at teaching hospitals in Perth, Western Australia (WA), and determine the risk factors and outcomes of the disease. We performed a retrospective case series analysis of all laboratory-confirmed episodes of S. aureus bacteraemia at Perth teaching hospitals between 1 July 1997 and 30 June 1999 by linking laboratory data with hospitalization data from the state's Hospital Morbidity Data System. Episodes of S. aureus bacteraemia were stratified according to methicillin susceptibility and the relationship between methicillin resistance and key factors or outcomes was determined. Almost 11% of episodes of S. aureus bacteraemia (55/509) were caused by MRSA. On age-adjusted multivariate analysis, Aboriginality (RR 6.71, 95% CI 3.20-14.10, P<0.001), geriatric unit admission (RR 5.74, 95% CI 2.01-16.37, P=0.001), female sex (RR 1.88, 95% CI 1.03-3.42, P=0.04) and healthcare-associated disease (RR 1.93, 95% CI 1.01-3.70, P=0.05) were independently associated with MRSA bacteraemia. Outcomes among those with MRSA bacteraemia included death in 15 patients and re-admission for an MRSA-related complication in five. Empirical use of vancomycin needs consideration in at-risk patients in whom Gram-positive bacteraemia is suspected clinically, with prompt review of therapy once antibiotic susceptibility results are known. The rates of re-admission after discharge for MRSA bacteraemia could be used as a clinical indicator to monitor the quality of care in hospitals.     

Generalized Additive Model Demonstrates Fluoroquinolone Use/Resistance Relationships for Staphylococcus Aureus

Mathematical models currently used to study the relationship between the prevalence of the resistance to an antibiotic and the amount of drug may not be adequate because they do not integrate temporal and area analyses simultaneously. Furthermore, the forms of such relationship are unknown. We applied the Generalized Additive Model (GAM) to study fluoroquinolone use and the incidence of fluoroquinolone-resistance in Staphylococcus aureus in our institution over a 3-year period. Overall institution and individual hospital unitrestricted analyses were performed. Relative risk (RR) observed for increasing fluoroquinolone use with a 4-month lag from the 25th percentile to the 75th percentile was 1.27 (95% CI: 1.13-1.42). In the surgery units, RR was 1.23 (95% CI: 1.01-1.50) for fluoroquinolone use with a 2-months lag. GAM enabled us to observe for the first time a significant temporal relationship between fluoroquinolone use and the incidence of fluoroquinolone-resistant nosocomial S. aureus isolates.     

Effect of reduction in ciprofloxacin use on prevalence of meticillin-resistant Staphylococcus aureus rates within individual units of a tertiary care hospital

Previous studies have shown a correlation between fluoroquinolone use in hospitals and rates of meticillin-resistant Staphylococcus aureus (MRSA) infection. This study examined the effect on MRSA infection rates within individual adult units of a tertiary care teaching hospital after instituting a programme to decrease ciprofloxacin use. Clinical specimens positive for S. aureus were determined on all adult inpatient units between 1 January 2004 and 31 December 2005. Units with >10 isolates of S. aureus per year were included in the analysis. Ciprofloxacin use, measured in defined daily doses per 1000 patient-days, was determined for each unit during the same time period. Ciprofloxacin use and MRSA rates for 2004 and 2005 were compared. In the 17 units studied, ciprofloxacin use decreased by 31.2% (P<0.0001). The MRSA rate in these units decreased from 59.6% to 54.2% (P=0.122). There was a correlation between ciprofloxacin use and the MRSA rate within these units (r=0.70; 95% confidence interval -0.01-0.94; P=0.053). Within individual units, there was a variable response. In seven of the units, there was an increase in the MRSA rate despite a reduction in ciprofloxacin use, suggesting that other factors (length of stay, infection control and community-acquired MRSA) may have contributed. Although many factors are associated with high MRSA rates, ciprofloxacin use appears to be a contributing factor. Reducing the use of ciprofloxacin may be a means of controlling MRSA in the hospital setting.     

1992～2001年烧伤病房病原菌分布及葡萄球菌耐药性分析

目的：了解近10年烧伤病区感染病原菌的变迁和葡萄球菌的耐药性。方法：比较1992-1996年和1997—2001年两组烧伤病人的创面培养、血培养和静脉导管培养结果，对细菌检出及葡萄球菌的药敏进行综合分析。结果：金黄色葡萄球菌的检出率占第一位，铜绿假单胞菌的检出率也在增加，尤其是血培养和静脉导管培养，两组比较，差异有显性(P＜0．05)。万古霉素对耐甲氧西林金黄色葡萄球菌(MRSA)有很高的抗菌活性，敏感性为100％，其次是复方新诺明，其余抗生素对MRSA的抗菌活性较差。结论：金黄色葡萄球菌和铜绿假单胞菌是烧伤病区的主要病原菌，万古霉素等糖肽类抗生素是治疗MRSA感染的可靠药物。     

Temporal changes in prevalence of antimicrobial resistance in 23 US hospitals

Antimicrobial resistance is increasing in nearly all health-care-associated pathogens. We examined changes in resistance prevalence during 1996-1999 in 23 hospitals by using two statistical methods. When the traditional chi-square test of pooled mean resistance prevalence was used, most organisms appear to have increased in prevalence. However, when a more conservative test that accounts for changes within individual hospitals was used, significant increases in prevalence of resistance were consistently observed only for oxacillin-resistant Staphylococcus aureus, ciprofloxacin-resistant Pseudomonas aeruginosa, and ciprofloxacin- or ofloxacin-resistant Escherichia coli. These increases were significant only in isolates from patients outside intensive-care units (ICU). The increases seen are of concern; differences in factors present outside ICUs, such as excessive quinolone use or inadequate infection-control practices, may explain the observed trends.     

Methicillin-resistant Staphylococcus aureus in Europe, 1999-2002

We explored the variation in proportions of methicillin-resistant Staphylococcus aureus (MRSA) between and within countries participating in the European Antimicrobial Resistance Surveillance System and temporal trends in its occurrence. This system collects routine antimicrobial susceptibility tests for S. aureus. We examined data collected from January 1999 through December 2002 (50,759 isolates from 495 hospitals in 26 countries). MRSA prevalence varied almost 100-fold, from <1% in northern Europe to >40% in southern and western Europe. MRSA proportions significantly increased in Belgium, Germany, Ireland, the Netherlands, and the United Kingdom, and decreased in Slovenia. Within countries, MRSA proportions varied between hospitals with highest variance in countries with a prevalence of 5% to 20%. The observed trends should stimulate initiatives to control MRSA at national, regional, and hospital levels. The large differences between hospitals indicate that efforts may be most effective at regional and hospital levels.     

Hospital preparedness and clinical description of the 2009 influenza A (H1N1) pandemic in a Belgian tertiary hospital

In our tertiary university hospital, fluoroquinolones were prohibited during 2001 leading to a 90% reduction in their use. Our objective was to examine the trends in meticillin-resistant Staphylococcus aureus (MRSA) following the reintroduction of fluoroquinolones. We conducted a 10-year time-series analysis of monthly MRSA according to: (i) period of fluoroquinolone restriction (January 2001 to January 2002); (ii) period of fluoroquinolone increase up to pre-restriction levels (January 2002 to December 2004); and (iii) an observational period including the implementation of a hand hygiene campaign with alcohol-based hand rub (January 2005 to June 2009). We used segmented linear autoregression analysis to assess trends between adjacent periods. Fluoroquinolone use increased from 5.2 defined daily doses (DDD) per 1000 patient-days in 2001 to 56.6 DDD per 1000 patient-days in 2005 reaching pre-restriction fluoroquinolone levels (P<0.001) and remained stable during 2005-2010 (P=0.65). The monthly proportion of MRSA decreased during the period of FQ restriction (-0.49 per month, P<0.05). The reintroduction of fluoroquinolones was associated with a significant increase in MRSA (+0.68 per month, P<0.02) compared to the previous period. During period 3, we observed a significant change in MRSA (-5.9, P<0.002) compared to the previous period (-0.32 per month, P<0.001). During the latter period, hand hygiene was promoted and alcohol-based hand-rub consumption increased from 3411 L in 2005 to 14,599 L in 2009. This study reinforces the rationale for a hospital-wide fluoroquinolone formulary policy to control MRSA and suggests that it has an additive effect with a hand hygiene promotion.     

Hospitalizations and deaths caused by methicillin-resistant Staphylococcus aureus, United States, 1999-2005

Hospital-acquired infections with Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA) infections, are a major cause of illness and death and impose serious economic costs on patients and hospitals. However, the recent magnitude and trend of these infections have not been reported. We used national hospitalization and resistance data to estimate the annual number of hospitalizations and deaths associated with S. aureus and MRSA from 1999 through 2005. During this period, the estimated number of S. aureus-related hospitalizations increased 62%, from 294,570 to 477,927, and the estimated number of MRSA-related hospitalizations more than doubled, from 127,036 to 278,203. Our findings suggest that S. aureus and MRSA should be considered a national priority for disease control.     

Temporal changes in bacterial resistance in German intensive care units, 2001-2003: data from the SARI (surveillance of antimicrobial use and antimicrobial resistance in intensive care units) project

Conservative testing revealed a stable antibiotic resistance situation for Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Enterobacter cloacae in 32 German intensive care units (ICUs) actively participating in the SARI (surveillance of antimicrobial use and antimicrobial resistance in ICUs) project over a three-year period (2001--2003). No significant changes were shown for methicillin-resistant S. aureus (MRSA) (P=0.501; the MRSA rate increased in 18 ICUs and decreased in 14 ICUs). The only exception was an increase in ciprofloxacin-resistant E. coli.     

2016-2018年内蒙古包头地区金黄色葡萄球菌耐药监测结果分析

目的 了解内蒙古包头地区金黄色葡萄球菌（Staphylococcus aureus,SAU）分离情况以及对抗菌药物的耐药变迁情况,为临床合理使用抗菌药物提供依据。 方法 收集2016-2018年内蒙古包头地区11家全国耐药监测网成员单位上报数据,对数据采用WHONET5.6软件进行统计分析。结果 2016-2018年检出金黄色葡萄球菌2613株,其中耐甲氧西林金黄色葡萄球菌（methicillin-resistant Staphylococcus aureus,MRSA）422株,检出率为16.2%（422/2613）。包钢医院的MRSA检出率最高,为30.9%（98/317）,包头市蒙医中医医院MRSA检出率最低,为1.9%（1/53）,检出率均低于全国平均水平。不同医院的金黄色葡萄球菌分离株对多数抗菌药物的耐药率不一致,如对复方新诺明耐药率最高是包头市第八医院,为52.3%,最低是包头市蒙医中医医院,为14.3%;对红霉素耐药率最高的是内蒙古北方重工业集团有限公司医院,为90.5%,最低的是包头市中心医院,为69.5%;对环丙沙星耐药率最高是内蒙古第一机械集团有限公司医院为26.2%,最低的是包头市肿瘤医院,为0,等。金黄色葡萄球菌对万古霉素、利奈唑胺、替考拉宁、替加环素的耐药率均为0。 结论 包头地区金黄色葡萄球菌总体控制较好,但耐药率仍较高。不同医院MRSA检出率不同,且各医院分离的金黄色葡萄球菌对常用抗菌药物的耐药性也不同。     

Low prevalence of methicillin-resistant Staphylococcus aureus (MRSA) at hospital admission in the Netherlands: the value of search and destroy and restrictive antibiotic use

In the Netherlands, less than 1% of clinical isolates of Staphylococcus aureus are methicillin-resistant (MRSA). A national search and destroy policy prevents MRSA from becoming endemic. Some MRSA outbreaks cannot be related to patients at risk for MRSA carriage. This study was designed to measure the prevalence of MRSA among patients without risk factors for MRSA carriage at the time of admission to the hospital. In four Dutch hospitals, patients admitted to non-surgical departments in the period 1999-2000 were screened for MRSA nasal carriage. Nasal swabs were streaked on 5% sheep blood agar (BA), submerged in a selective broth, and incubated for two to three days at 35 degrees C. Colonies suspected of being S. aureus were identified with an agglutination test. Susceptibility testing was performed by an automated system and additional oxacillin disk diffusion. Methicillin resistance was confirmed by a DNA hybridization test and mecA PCR. MRSA strains were genotyped by pulsed-field gel electrophoresis (PFGE). Twenty-four percent (2332/9859) of the patients were S. aureus nasal carriers. Only three (0.03%) patients were MRSA carriers. These patients were not repatriated, nor known to be MRSA carriers before screening. Genotyping revealed that the strains were not clonally related and were not related to MRSA outbreaks in the hospital where the patients were admitted. We conclude that at routine admission to a Dutch hospital (excluding high-risk foreign admissions) the MRSA prevalence is low (0.03%), due to the Dutch search and destroy policy and restrictive antibiotic prescribing.     

湖北地区临床细菌耐药性监测

目的：调查湖北地区临床分离菌对抗菌药物的耐药状况。方法：将湖北地区15所医院纸片扩散法药敏试验的抑菌环直径输入计算机;根据1999年NCCLS颁布的准则,采用“WHONET－5”软件完成统计分析。结果：临床分离菌中革兰阳性球菌有增多趋势;金黄色葡萄球菌（金葡菌）、大肠埃希菌、铜绿假单胞菌和凝固酶阴性葡萄球菌（CNS）最常见;31．0％金葡菌和67．6％CNS对苯唑西林耐药,对其他药物的耐药率也高;亚胺培南、头孢他啶、阿米卡星和环丙沙星对革兰阴性杆菌（包括肠杆菌科细菌和非发酵菌）,有良好的抗菌活性,但与1996年监测资料比较,敏感率均在显著下降。结论：临床细菌耐药性日益严重,应在不同地区开展细菌耐药性监测;强调临床合理应用抗菌药物。     

Mupirocin for controlling methicillin-resistant Staphylococcus aureus: lessons from a decade of use at a university hospital.

BACKGROUND: From 1990 to 1995 at Hospital Universitário Clementino Fraga Filho, patients colonized or infected with methicillin-resistant Staphylococcus aureus (MRSA) were treated with mupirocin to eliminate MRSA carriage. In 1995, 65% of MRSA patients at this hospital had mupirocin-resistant isolates. Starting in 1996, mupirocin use was restricted to patients colonized, but not infected, with MRSA. OBJECTIVES: To describe the use of mupirocin for controlling MRSA over a decade and to analyze the molecular epidemiology of mupirocin-resistant MRSA infections at this hospital. SETTING: A 490-bed, tertiary-care university hospital. METHODS: The incidence densities of patients with MRSA and acquisition of mupirocin by the hospital were calculated for the period 1992-2001. S. aureus isolates from 1999-2000 were analyzed by pulsed-field gel electrophoresis. Mupirocin-resistant MRSA isolates from 1994-1995 and 1999-2000 were analyzed for ileS-2 gene background polymorphisms. RESULTS: The incidence density of MRSA patients increased slightly over time, whereas the purchase of mupirocin decreased dramatically. Mupirocin-resistant MRSA infections decreased from 65% in 1994-1995 to 15% in 1999-2000. The MRSA Brazilian clone, detected in 1992, was still highly prevalent. The same ileS-2 encoding plasmid found in 1994-1995 persisted in three identical MRSA isolates from 1999-2000 belonging to the Brazilian clone. CONCLUSIONS: After mupirocin use decreased, the ileS-2 encoding plasmid persisted in only a few Brazilian clone isolates. Our data on mupirocin-resistant MRSA incidence and mupirocin use strongly suggested that restricted use was related to decreased rates of mupirocin resistance at our hospital.     

Methicillin-resistant Staphylococcus aureus in a teaching hospital: investigation of nosocomial transmission using a matched case-control study

In early 1996 a hospital-wide methicillin-resistant Staphylococcus aureus (MRSA) epidemic was recognized in a 900-bed university hospital. In order to investigate hospital-specific transmission routes, a case-control study was carried out. Cases and controls were matched for age (+/- 10 years), sex, admission date (+/- 10 days) and clinical department on admission. Data on potential risk factors, were retrieved by chart review. Between June 1996 and February 1997, 67 patients with hospital-acquired MRSA were identified. Molecular typing showed that 85% of the cases carried an indistinguishable strain. The average time at risk for cases and controls was 17.3 and 23.7 days, respectively (P= 0.01). Seventeen patients (25.4%) developed infection. Conditional multivariate regression analysis showed that intensity of care (P= 0.002), number of transfers (P= 0.019), and fluoroquinolone therapy (P= 0.025) were independently associated with acquisition of MRSA. Intensity of care can be considered as a surrogate marker for a number of manipulations which represent the main risk factors for MRSA transmission. Frequent transfers within the hospital hinder, not only the epidemiological analyses, but also efforts to bring an outbreak under control. Our findings give epidemiological support to recent molecular studies which suggest that fluoroquinolone use may increase the transmissibility of MRSA in hospitals.     

Imipenem resistance among pseudomonas aeruginosa isolates: risk factors for infection and impact of resistance on clinical and economic outcomes.

OBJECTIVES: To identify risk factors for infection with imipenem-resistant Pseudomonas aeruginosa and determine the impact of imipenem resistance on clinical and economic outcomes among patients infected with P. aeruginosa. DESIGNS: An ecologic study, a case-control study, and a retrospective cohort study. SETTING: A 625-bed tertiary care medical center. PATIENTS: All patients who had an inpatient clinical culture positive for P. aeruginosa between January 1, 1999, and December 31, 2000. RESULTS: From 1991 through 2000, the annual prevalence of imipenem resistance among P. aeruginosa isolates increased significantly (P<.001 by the chi (2) test for trend). Among 879 patients infected with P. aeruginosa during 1999-2000, a total of 142 had imipenem-resistant P. aeruginosa infection (the case group), whereas 737 had imipenem-susceptible P. aeruginosa infection (the control group). The only independent risk factor for imipenem-resistant P. aeruginosa infection was prior fluoroquinolone use (adjusted odds ratio, 2.52 [95% confidence interval {CI}, 1.61-3.92]; P<.001). Compared with patients infected with imipenem-susceptible P. aeruginosa, patients infected with imipenem-resistant P. aeruginosa had longer subsequent hospitalization durations (15.5 days vs 9 days; P=.02) and greater hospital costs (81,330 dollars vs 48,381dollars ; P<.001). The mortality rate among patients infected with imipenem-resistant P. aeruginosa was 31.1%, compared with 16.7% for patients infected with imipenem-susceptible P. aeruginosa (relative risk, 1.86 [95% CI, 1.38-2.51]; P<.001). In multivariable analyses, there remained an independent association between infection with imipenem-resistant P. aeruginosa and mortality. CONCLUSIONS: The prevalence of imipenem resistance among P. aeruginosa strains has increased markedly in recent years and has had a significant impact on both clinical and economic outcomes. Our results suggest that curtailing use of other antibiotics (particularly fluoroquinolones) may be important in attempts to curb further emergence of imipenem resistance.     

Evaluation of an intervention designed to decrease the rate of nosocomial methicillin-resistant Staphylococcus aureus infection by encouraging decreased fluoroquinolone use.

OBJECTIVE: Society for Health Care Epidemiology guidelines recommend decreasing the use of fluoroquinolone antibiotics in institutions where methicillin-resistant Staphylococcus aureus (MRSA) is endemic. We evaluated whether an intervention to limit fluoroquinolone use was associated with a lower rate of nosocomial MRSA infection and summarized changes in antibiotic use, changes in other variables potentially correlated with a lower rate of MRSA infection, and rates of nosocomial infections due to other pathogens. DESIGN: Single-center quasi-experimental design. A time series of nosocomial MRSA infections was measured at monthly intervals from July 2001 through June of 2004; there were 80 MRSA infections recorded. Segmented regression analysis (ie, quasi-Poisson generalized linear models) was used to evaluate variables possibly associated with the nosocomial MRSA infection rate. SETTING: An 87-bed Veterans Affairs teaching hospital with an extended-care facility. INTERVENTION: A physician-directed computer-generated intervention designed to limit the use of fluoroquinolone antibiotics was initiated, and institutional changes in antibiotic use and nosocomial MRSA infection rates were tracked. RESULTS: After the intervention, fluoroquinolone use decreased by approximately 34%, and levofloxacin use decreased by approximately 50%. Decreased fluoroquinolone use was offset by increased cephalosporin, piperacillin-tazobactam, and trimethoprim-sulfamethoxazole use. The nosocomial MRSA infection rate decreased from 1.37 to 0.63 episodes per 1,000 patient-days after the study intervention (P=.02). Coagulase-negative Staphylococcus and Enterococcus infection rates also decreased. However, the rate of infection with gram-negative organisms increased. The rate of MRSA infection was positively correlated with levofloxacin use (P=.01) and azithromycin use (P=.08), whereas it was negatively correlated with summer season (P=.05). In a subsequent model, the rate of MRSA infection was negatively correlated with the study intervention (P=.04). CONCLUSION: Reduction in the institutional use of fluoroquinolones may be associated with a lower nosocomial MRSA infection rate.     

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.     

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.