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

Coevolution: mankind and microbes

In just 70 short years mankind has progressed from euphoria to despair over the effectiveness of antibiotics to protect and to cure mankind from morbidity and mortality from infectious diseases. Resistance due to evolutionary factors was observed shortly after antibiotics came into use and is now not only widespread but appears to be inevitable. This review is a rather personalized account of the various attempts to deal with this problem over time.

Risk factors and mortality in patients with nosocomial Staphylococcus aureus bacteremia

BACKGROUND

Infections due to methicillin-resistant Staphylococcus aureus have become increasingly common in hospitals worldwide. S aureus continues to be a cause of nosocomial bacteremia.

METHODS

We analyzed the clinical significance (mortality) of MRSA and methicillin-susceptible S aureus bacteremia in a retrospective cohort study in a 2900-bed tertiary referral medical center. Survival and logistic regression analyses were used to determine the risk factors and prognostic factors of mortality.

RESULTS

During the 15-year period, 1148 patients were diagnosed with nosocomial S aureus bacteremia. After controlling potential risk factors for MRSA bacteremia on logistic regression analysis, service, admission days prior to bacteremia, age, mechanical ventilator, and central venous catheter (CVC) were independent risk factors for MRSA. The crude mortality rate of S aureus bacteremia was 44.1%. The difference between the mortality rates of MRSA (49.8%) and MSSA bacteremia (27.6%) was 22.2% (P < .001). Upon logistic regression analysis, the mortality with MRSA bacteremia was revealed to be 1.78 times higher than MSSA (P < .001). The other predicted prognostic factors included age, neoplasms, duration of hospital stay after bacteremia, presence of mechanical ventilator, and use of CVC.

CONCLUSIONS

Resistance to methicillin was an important independent prognostic factor for patients with S aureus bacteremia.

5 Million Lives Campaign. Case study: an MRSA intervention at Evanston Northwestern Healthcare

PCR-based testing offers superiority to culture in reduction of unisolated days. The ICU-based surveillance intervention had little impact after one year with surveillance compliance at 67%. However, once compliance improved, surveillance was expanded to the entire hospital and decolonization was implemented, MRSA BSIs were significantly reduced. Our experience parallels that of the European countries and other United States facilities that have implemented aggressive MRSA control measures. All successful programs have included active surveillance testing and barrier precautions. Finally, according to the Centers for Disease Control and Prevention's just-released report on invasive MRSA, since most MRSA infections are associated with health care contact, strategies to prevent and control MRSA among inpatients still may have a positive impact on infection, as demonstrated by our intervention.

Surveillance of antibacterial resistance in Staphylococcus aureus isolated in Kuwaiti hospitals

OBJECTIVE

To investigate the prevalence of antibiotic resistance among Staphylococcus aureus isolated in Kuwaiti hospitals.

MATERIALS AND METHODS

S. aureus were isolated and identified following standard microbiological methods. Antibacterial susceptibility test was performed by disk diffusion and the measurement of minimum inhibitory concentration with E-test strips.

RESULTS

A total of 1,846 S. aureus isolates were analyzed from 13 hospitals between 1 March and 30 October 2005. They were isolated from 1,765 (95.6%) inpatients and 81 (4.4%) outpatients. Methicillin resistance was detected in 588 (32.0%) of the isolates. The methicillin-resistant S. aureus (MRSA) consisted of 461 (78%) multiresistant and 127 (22%) nonmultiresistant isolates. The nonmultiresistant MRSA consisted of epidemic MRSA-15 and community-associated MRSA. The community-associated MRSA was detected in all hospitals with MRSA, indicating its establishment in Kuwaiti hospitals. The proportion of isolates resistant to gentamicin, kanamycin, erythromycin, tetracycline, ciprofloxacin, fusidic acid and trimethoprim was higher among MRSA than methicillin-susceptible S. aureus (MSSA) isolates. Twenty-four and 22% of MRSA and MSSA isolates, respectively, expressed reduced susceptibility to vancomycin (minimum inhibitory concentration = 3-4 mg/l).

CONCLUSION

The study revealed the presence of methicillin resistance in 32% of S. aureus isolated in Kuwaiti hospitals and revealed an increase in the number of MRSA and MSSA with reduced susceptibility to vancomycin.

Monoclonal antibodies for prophylaxis and therapy of infectious diseases

Monoclonal antibodies (mAb) are attractive biologic drugs due to their exquisite specificity and well understood mechanisms of action, which results in a higher predictability and lower attrition rate compared with other drugs. Therefore, it may seem surprising that only a single mAb is presently marketed for an infectious disease indication. However, the antibiotic resistance crisis, emerging viral diseases and bioterroristic threats have recently spurred the development of anti-infective mAbs, of which more than a dozen are being tested in clinical trials. Conceptually, and validated in many preclinical models, mAbs will be most effective when used prophylactically against acute viral infections and bacterial toxins. The acute bacterial and chronic viral infections, which are medically and economically far more important, are much more difficult to control by antibodies, as the recent clinical failure of some polyclonal antibody products has shown. In these situations, the synergistic action of two or more mAbs together with a small molecule drug will most likely be required for therapeutic efficacy. This review aims to highlight the scientific and economic opportunities and obstacles that are encountered in the quest to add mAbs to the armament of anti-infective drugs.

Methicillin-resistant Staphylococcus aureus as a cause of extensive retropharyngeal abscess in two infants

We report 2 cases of extensive methicillin-resistant Staphylococcus aureus (MRSA) retropharyngeal abscesses in young infants. In 1 case, the abscess was associated with a reactive thrombosis of the jugular vein. Based on the existing literature and the rapid emergence of MRSA skin and soft tissue infections, it is possible that similar severe infections will occur with increasing frequency in young infants.

Is MRSA more virulent than MSSA?

Numerous clinical studies have indicated, based on mortality rates, that methicillin-resistant Staphylococcus aureus (MRSA) strains are more virulent than methicillin-susceptible S. aureus (MSSA) strains. In contrast, quantitative laboratory examinations of the presence and magnitude of pathogenic mechanisms and virulence factors in strains of MRSA and MSSA have generated conflicting data. The most important reason for these conflicting results is probably the heterogeneic nature of the resistant population. A comparison of selected and congenic MRSA and MSSA sub-populations of the same strain is required to resolve this issue.

Impact of rapid molecular screening for meticillin-resistant Staphylococcus aureus in surgical wards

Background

This study aimed to establish the feasibility and cost-effectiveness of rapid molecular screening for hospital-acquired meticillin-resistant Staphylococcus aureus (MRSA) in surgical patients within a teaching hospital.

Methods

In 2006, nasal swabs were obtained before surgery from all patients undergoing elective and emergency procedures, and screened for MRSA using a rapid molecular technique. MRSA-positive patients were started on suppression therapy of mupirocin nasal ointment (2 per cent) and undiluted chlorhexidine gluconate bodywash.

Results

A total of 18 810 samples were processed, of which 850 (4·5 per cent) were MRSA positive. In comparison to the annual mean for the preceding 6 years, MRSA bacteraemia fell by 38·5 per cent (P &lt; 0·001), and MRSA wound isolates fell by 12·7 per cent (P = 0·031). The reduction in MRSA bacteraemia and wound infection was equivalent to a saving of 3·78 beds per year (£276 220), compared with the annual mean for the preceding 6 years. The cost of screening was £302 500, making a net loss of £26 280. Compared with 2005, however, there was a net saving of £545 486.

Conclusion

Rapid MRSA screening of all surgical admissions resulted in a significant reduction in staphylococcal bacteraemia during the screening period, although a causal link cannot be established.

Screening for methicillin-resistant Staphylococcus aureus in clinical swabs using a high-throughput real-time PCR-based method

The presence of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals and the community is a serious problem. Accordingly, a comprehensive plan has been implemented in the County of Vejle, Denmark, to identify colonised and/or infected individuals and to control the spread of MRSA. Since 2005, all patients and healthcare personnel have been screened for MRSA colonisation, involving analysis of 300-400 samples daily. To deal with this number of samples, a PCR-based method customised for high-throughput analysis and a system for fast reporting of MRSA carrier status were developed. Swab samples were incubated overnight in a selective tryptone soya broth and were analysed by PCR the following day. Using this strategy, non-colonised individuals were identified within 24 h, while MRSA-positive samples were analysed further by traditional microbiological methods to determine the resistance pattern. This is a cost-effective approach, as the greatest expense in hospitals involves the isolation of patients of unknown MRSA status. The method was evaluated by testing 2194 clinical samples, with a sensitivity and specificity of 100% and 94%, respectively. The analytical sensitivity was 97%, with 161 of 166 different MRSA strains and isolates generating positive results according to PCR analysis. Using four control strains, the inter-assay variation was revealed to be a maximum of 2.6%, indicating good reproducibility.

Emergence in Brazil of methicillin-resistant Staphylococcus aureus isolates carrying SCCmecIV that are related genetically to the USA800 clone

An increasing incidence of nosocomial infections caused by non-multiresistant methicillin-resistant Staphylococcus aureus (nMMRSA) has been reported worldwide. The present study genotyped nMMRSA isolates obtained from hospitals in two cities in Brazil. The hospital isolates displayed pulsed-field gel electrophoresis (PFGE) patterns that were similar to those of the USA100 (ST5-SCCmecII) and USA 800 (ST5-SCCmecIV) strains, which are related to the New York/Japan and paediatric clones, respectively. Carriage of SCCmecIV and the classification by multilocus sequence typing (MLST) of a representative of this PFGE pattern in clonal complex 5 (CC5) confirmed the genetic relationship of the Brazilian isolates with USA800. The USA800-related Brazilian isolates were responsible for severe nosocomial infections in compromised adults and elderly patients in Brazil. A higher growth rate, an ability to form biofilm on inert polystyrene surfaces and the presence of the egc locus may have contributed, at least in part, to the fitness of these organisms as global nosocomial pathogens.

Risk factors for meticillin resistance and outcome of Staphylococcus aureus bloodstream infection in a Belgian university hospital

The aim of this study was to identify institution-specific risk factors for meticillin resistance in Staphylococcus aureus bloodstream infection (BSI) and to evaluate the impact of meticillin resistance on mortality. A total of 154 episodes of S. aureus BSI were identified between 1 January 2002 and 31 December 2004: 66 meticillin-resistant S. aureus (MRSA) BSI and 88 meticillin-susceptible S. aureus (MSSA) BSI. Seventy-eight episodes (51%) were considered to be community-acquired and 76 (49%) as nosocomial. Risk factors associated with MRSA BSI included not living at home (P=0.001), prior antibiotic exposure (P=0.002), insulin-requiring diabetes (P=0.028) and nosocomial BSI (P=0.031), especially more than 12.5 days after admission. There was an association between BSI-related mortality and the following variables: septic shock (P<0.001), endocarditis (P=0.002) and MRSA BSI (P=0.021). In conclusion, S. aureus BSI is a serious condition, especially when septic shock or endocarditis occurs, and is aggravated by meticillin resistance. We advise glycopeptides as empirical therapy for patients not arriving from home, those exposed to antibiotics, and those with insulin-requiring diabetes and/or nosocomial BSI.

The development of a new three-step protocol to determine the efficacy of disinfectant wipes on surfaces contaminated with Staphylococcus aureus

We developed a three-step protocol to quantify the efficacy of disinfectant wipes, their ability to remove and prevent microbial transfer from surfaces and their overall antimicrobial activity. Meticillin-resistant (MRSA) or -susceptible (MSSA) Staphylococcus aureus (6-7 log(10)cfu) were inoculated onto stainless steel discs with or without organic load and dried. Grapefruit extract-containing test wipes and unmedicated control wipes were used. In step 1, wipes were mechanically rotated against surfaces for 10s at 60rpm, exerting a weight of 100+/-5g. Bacterial removal was assessed by transferring the steel discs to neutraliser, resuspending and counting remaining bacteria. In step 2, bacterial transfer from wipes was assessed by eight consecutive mechanical adpression transfers to agar/neutraliser plates. Step 3 was the measurement of antimicrobial activity by direct inoculation of the wipes for 10s followed by neutralisation and enumeration. Test wipes achieved a significantly higher bacterial cell removal than control wipes on all surfaces (P<0.05). The low bactericidal activity of the wipes (<1 log(10) reduction when directly inoculated) and the subsequent survival of bacteria on the wipes, however, led to repeated microbial transfer when initially high contamination levels were present. There were no differences between MRSA and MSSA in removal, transfer or antimicrobial activity. The three-step method is a useful tool for developing future guidelines to assess the ability of wipes to disinfect surfaces.

Epidemiology of staphylococcal resistance

An understanding of the prevalence of resistant Staphylococcus aureus and the risk factors for infection with resistant isolates is essential to help clinicians choose appropriate antibiotic therapy. Selection pressure due to prior and inappropriate antibiotic use of any kind seems to be the main driving force behind the increasing rates of multidrug resistance in methicillin-resistant S. aureus (MRSA) strains. Resistance to glycopeptide antibiotics in MRSA has also emerged in recent years, along with increased use of vancomycin to treat serious infections due to MRSA. Infections due to MRSA are associated with significantly increased morbidity, mortality, length of hospital stay, and costs, compared with infections due to methicillin-susceptible S. aureus, despite adjustment for disease severity and initially appropriate antibiotic treatment. Improvements in the preparation and dissemination of antibiograms, along with adequate public reporting of MRSA trends, are needed to address the challenge of choosing appropriate initial antibiotic treatment for MRSA infections.

Daptomycin in the treatment of bacteremia

The aim of this study was to describe the clinical experience with daptomycin in the treatment of bacteremia. Patients with a diagnosis of catheter-related or non-catheter-related bacteremia and no other concurrent infection were identified from the Cubicin Outcomes Registry and Experience (CORE) 2004. Treatment success was determined by investigators using protocol criteria and defined as cure or improvement. Of 168 patients with bacteremia, 126 were clinically evaluable. Of those, 52 (41%) patients were aged > or =66 years, 54 (43%) received daptomycin in an intensive care unit, and 25 (20%) had chronic renal failure. The most common pathogens isolated were methicillin-resistant Staphylococcus aureus (33%), vancomycin-resistant enterococci (30%), and coagulase-negative staphylococci (30%). Of 126 patients, 86% received daptomycin after previous antibiotic therapy and most (69%) received concomitant antibiotics with daptomycin. Daptomycin therapy was started at a median dose of 4.0 mg/kg (range, 2.5 to 9.2 mg/kg). Daptomycin therapy had an overall clinical success rate of 89%. Clinical success was independent of baseline renal function, daptomycin dose, pathogen, first-line use, or concomitant antibiotic therapy. These results support the findings of a recent study in which daptomycin was demonstrated to be an effective option in the treatment of S aureus bacteremia. Data in the current study provide insight into the clinical experience using daptomycin to treat bacteremia caused by other gram-positive pathogens. Given the limitations of retrospective studies and lack of follow-up data, additional studies are needed to make definitive evaluations with these pathogens.

Measuring the impact of multidrug resistance in nosocomial infection

PURPOSE OF REVIEW

The review examines potential confounders hampering measurement of the impact of multidrug resistance in nosocomial infections. Methodological techniques dealing with the problem of confounding are discussed and current findings in how multidrug resistance affects outcome in patients with nosocomial infection are highlighted.

RECENT FINDINGS

Outcome comparisons between patients infected with multidrug-resistant pathogens and patients infected with susceptible microorganisms are hampered by confounders such as differences in disease severity, prolonged hospitalization prior to onset of infection (exposure time), the causative pathogen, the type of infection, and the rate of appropriate empirical antimicrobial therapy. The confounding effect can be countered by means of either multivariable regression techniques or matched cohort studies, or a combination of both. Recent literature on the impact of multidrug resistance (methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, extended-spectrum beta-lactamase producing Enterobacteriaceae, etc) is conflicting and highly dependable on the way disturbing variables are accounted for.

SUMMARY

Recent data underscore that the impact of multidrug resistance on the outcome of nosocomial infection might differ depending on the study population, type of infection, type of pathogen and appropriateness of therapy, and hence, that any conclusion drawn prior to accurate accounting for imbalanced confounders is premature and potentially false.

Perspectives on Daptomycin Resistance, with Emphasis on Resistance in Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus infections are becoming more frequent and less easily treated by means of currently recommended agents. Vancomycin has been associated with decreased susceptibility in staphylococci and with treatment failures. Daptomycin is rapidly bactericidal; a dosage of 4 mg/kg daily is approved for treatment of skin and soft-tissue infections, and a dosage of 6 mg/kg daily is approved for treatment of patients with S. aureus bacteremia and right-sided endocarditis. Findings of in vitro studies suggest a correlation between the minimum inhibitory concentrations of daptomycin and vancomycin. Clinical failure was associated with increasing minimum inhibitory concentrations in case reports and in a randomized study of persons with S. aureus bacteremia and endocarditis. Patients who did not respond to therapy had deep-seated infections that required but could not be or were not managed with adjunctive surgical therapy. No definitive resistance mechanism has been identified, although genetic mutations have been described. Clinically, prior vancomycin therapy has not been associated with failure of daptomycin therapy. Although clinical practitioners must monitor for daptomycin resistance, the available data support the use of daptomycin in the treatment of methicillin-resistant S. aureus bacteremia and endocarditis.

Burden of methicillin-resistant Staphylococcus aureus: focus on clinical and economic outcomes

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a major public concern. Hospital-acquired MRSA rates have steadily increased over the past 25 years, and the bacterial strain is making inroads to the community. The morbidity and mortality burden of MRSA infection is compounded by delayed or inappropriate antibiotic treatment, taking a toll on health care resources that are already stretched thin. Vancomycin has historically been the drug of choice for this pathogen because its broad spectrum can address the multidrug resistance of most MRSA infections. Despite its sustained in vitro microbiologic inhibitory activity, researchers are beginning to question the continued utility of vancomycin for MRSA infections. Evidence against vancomycin is most notable with regard to nosocomial pneumonia and skin and soft tissue infections. In addition, because vancomycin must be administered intravenously, patients typically require prolonged hospitalization, which further increases the cost of MRSA treatment and exposes patients to additional nosocomial infections. Recent studies have shown that antibiotics with good bioavailability, such as linezolid, can be given orally to facilitate early hospital discharge, thus alleviating the economic burden of MRSA infections. Several agents have been developed over the past decade that have excellent in vitro activity against MRSA. Further studies are needed to determine if these drugs can better eradicate MRSA than vancomycin and remedy the adverse outcomes frequently observed with this organism.

Selective use of intranasal mupirocin and chlorhexidine bathing and the incidence of methicillin-resistant Staphylococcus aureus colonization and infection among intensive care unit patients

OBJECTIVE

To determine whether the use of chlorhexidine bathing and intranasal mupirocin therapy among patients colonized with methicillin-resistant Staphylococcus aureus (MRSA) would decrease the incidence of MRSA colonization and infection among intensive care unit (ICU) patients.

METHODS

After a 9-month baseline period (January 13, 2003, through October 12, 2003) during which all incident cases of MRSA colonization or infection were identified through the use of active-surveillance cultures in a combined medical-coronary ICU, all patients colonized with MRSA were treated with intranasal mupirocin and underwent daily chlorhexidine bathing.

RESULTS

After the intervention, incident cases of MRSA colonization or infection decreased 52% (incidence density, 8.45 vs 4.05 cases per 1,000 patient-days; P=.048). All MRSA isolates remained susceptible to chlorhexidine; the overall rate of mupirocin resistance was low (4.4%) among isolates identified by surveillance cultures and did not increase during the intervention period.

CONCLUSIONS

We conclude that the selective use of intranasal mupirocin and daily chlorhexidine bathing for patients colonized with MRSA reduced the incidence of MRSA colonization and infection and contributed to reductions identified by active-surveillance cultures. This finding suggests that additional strategies to reduce the incidence of MRSA infection and colonization--beyond expanded surveillance--may be needed.

Higher risk of failure of methicillin-resistant Staphylococcus aureus prosthetic joint infections

We determined the effect of methicillin resistance on the outcome of patients with Staphylococcus aureus prosthetic joint infections. From January 1995 to December 2004, 33% of 137 episodes of prosthetic joint infections were the result of S. aureus (in monomicrobial or polymicrobial cultures). Thirty-three (24%) episodes among 31 patients were the result of methicillin-susceptible S. aureus and 12 (9%) episodes among 12 patients were the result of methicillin-resistant S. aureus. Overall treatment failure rate was 38%. Patients with methicillin-susceptible S. aureus or methicillin-resistant S. aureus prosthetic joint infections did not differ in age, gender, comorbidities, joint age, prior surgical procedures performed on the affected joint, number of postsurgical medical complications, or duration of intravenous antimicrobial therapy. Patients with methicillin-resistant S. aureus prosthetic joint infection had longer hospital durations (median, 15 versus 10 days). Methicillin-resistant S. aureus in periprosthetic tissue culture resulted in a higher risk of treatment failure (hazard ratio, 9.2; 95% confidence interval, 2.40-35.46) than methicillin-susceptible S. aureus when controlling for joint location (total knee arthroplasty versus total hip arthroplasty [hazard ratio, 5.8; 95% confidence interval, 1.52-22.19]) and removal of hardware (hazard ratio, 0.24; 95% confidence interval, 0.077-0.75). Efforts should be made to prevent methicillin-resistant S. aureus infections of joint arthroplasties and develop new treatment modalities.

Lack of effect of fluoroquinolone resistance on mortality in subjects with Pseudomonas aeruginosa bacteraemia

OBJECTIVES

Despite the well-documented increase in fluoroquinolone resistance to Pseudomonas aeruginosa, the effect on pathogenicity is unknown. This paper will explore the clinical effect.

METHODS

A retrospective, observational, cohort study of 215 hospital inpatients was performed. Subjects with fluoroquinolone-resistant P. aeruginosa (FQRPA) bacteraemia were compared to subjects with fluoroquinolone-sensitive P. aeruginosa (FQSPA) bacteraemia from January 2000 to December 2003. Mortality prior to discharge, time to discharge, and time to negative culture were assessed. Additionally, baseline morbidity/mortality risk factors including Charlson morbidity score (CMS) were assessed.

RESULTS

Mortality prior to discharge (32 vs. 29%, P=0.73), mean days to discharge (17.5 vs. 14.6, P=0.24), and mean days to negative culture (3.6 vs. 3.2, P=0.1) did not differ between FQRPA and FQSPA, respectively. Active antibiotic treatment within 24h of drawn blood culture (FQRPA 63% vs. FQSPA 93%, P<0.0001) and median CMS (FQRPA 3 vs. FQSPA 5, P=0.004) differed significantly between the groups.

CONCLUSIONS

Subjects with FQRPA received active antibiotics less often within 24h of obtained culture. A large difference in mortality does not likely exist based on fluoroquinolone susceptibility. A study with greater enrollment must be conducted to determine if fluoroquinolone resistance imparts a smaller yet clinically significant impact on clinical outcomes.

Daptomycin

There has been a steady rise in the prevalence of resistant Gram-positive pathogens and concerns about the clinical effectiveness of glycopeptides in treating infections due to Staphylococcus aureus. Daptomycin is a novel lipopeptide antimicrobial agent with activity against Gram-positive organisms, including multi-resistant strains. It is licensed in the USA and Europe for the treatment of complicated skin and soft tissue infections caused by Gram-positive organisms at a dose of 4mg/kg once daily. It has also been licensed in the USA for the treatment of S. aureus bacteraemia and right-sided endocarditis at 6mg/kg once daily. It is a safe and well-tolerated antibiotic, particularly at the current dosing regimen. Antimicrobial resistance, whilst being increasingly reported, still remains relatively rare. Further studies are required to determine the role of daptomycin for the treatment of osteomyelitis and septic arthritis, as well as its use in combination therapy.

Instrumentation, data evaluation and quantification in on-line aerosol mass spectrometry

On-line micro- and nanoparticle mass spectrometry has evolved into a prominent analytical method for the characterization of airborne particles, particle populations and aerosols over the recent years, driven by essential developments in instrumentation, data evaluation and validation. In this tutorial, the fundamental aspects of the technology and methodology for qualitative and quantitative on-line aerosol particle analysis are discussed. Specific properties of the on-line mass spectrometric instrumentation for particle analysis are described, combined with a discussion of basic differences of the instruments and demands for future improvements of instruments and data analysis techniques. Optimized technology and methodology in particle analysis is expected to lead to essential growth of the knowledge and to quality improvement of the description of atmospheric processes and health effects in the future.

Impact of methicillin-resistant Staphylococcus aureus infection on outcome after esophagectomy

BACKGROUND

Infection with methicillin-resistant Staphylococcus aureus (MRSA) has reached endemic proportions in the United Kingdom. The aim of the present study was to determine the frequency of MRSA infection in patients undergoing esophagectomy and to report its impact on patient outcome.

PATIENTS AND METHODS

The study population was 98 patients undergoing esophagectomy for carcinoma during the years 1998-2004. Patient information was collected prospectively and entered into a computerized database and analyzed retrospectively by univariate and multivariate analysis.

RESULTS

Overall, 20 of the 98 patients (20%) developed infection with MRSA after esophagectomy. Patients who developed MRSA infection had greater levels of postoperative morbidity, longer intensive care unit (ICU) stays (median 2 days versus 1 day, P = 0.005) and hospital stays (21 days versus 16 days, P < 0.001) compared to those who did not develop infection. Multivariate analysis identified preoperative chemotherapy (P = 0.006) and readmission to the ICU (P = 0.007) as significant risk factors with MRSA infection. Overall, 17 of 46 patients (37%) who received neoadjuvant chemotherapy developed MRSA infection, compared to 3 of 52 (6%) who did not receive this treatment (P = 0.0001).

CONCLUSIONS

Overall, one in five patients undergoing esophagectomy developed MRSA infection, with those patients who received neoadjuvant chemotherapy identified as being at greatest risk of this complication. This is an alarming finding, as neoadjuvant chemotherapy is the standard of care for patients with esophageal carcinoma in the United Kingdom.

Clinical validation of the molecular BD GeneOhm StaphSR assay for direct detection of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus in positive blood cultures

The rapid detection of Staphylococcus aureus bacteremia and a swift determination of methicillin susceptibility has serious clinical implications affecting patient mortality. This study evaluated the StaphSR assay (BD GeneOhm, San Diego, CA), a real-time PCR assay, for the identification and differentiation of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) from 300 positive blood cultures. The BD GeneOhm StaphSR assay was performed and interpreted according to the manufacturer's recommendations. Positive blood cultures (containing predominantly gram-positive cocci in clusters) were subcultured on 5% sheep blood agar plates. After 18 to 24 h of incubation, isolates morphologically consistent with S. aureus were presumptively identified by latex agglutination (Staphaurex Plus; Remel, Lenexa, KS). Susceptibility testing was initially performed with the Phoenix automated microbiology system (BD Diagnostics, Sparks, MD). Additional susceptibility testing of samples with discrepant results was done using BBL oxacillin screen agar (BD Diagnostics, Sparks, MD), oxacillin and cefoxitin Etests (AB Biodisk, Solna, Sweden) on Mueller-Hinton agar, an immunoassay for penicillin binding protein 2' (Denka Seiken Co., Tokyo, Japan), and mecA PCR. The sensitivity, specificity, and positive and negative predictive values of the BD GeneOhm StaphSR assay for MSSA detection were 98.9, 96.7, 93.6, and 99.5%, respectively. For the detection of MRSA, the BD GeneOhm StaphSR assay was 100% sensitive and 98.4% specific; positive and negative predictive values for MRSA detection were 92.6 and 100%, respectively. Inhibition was seen with only one sample, and the issue was resolved upon retesting. The BD GeneOhm StaphSR assay appears to be a valuable diagnostic tool for quickly differentiating bacteremia caused by MSSA and MRSA from that caused by other gram-positive cocci.

Predictive factors of meticillin resistance among patients with Staphylococcus aureus bloodstream infections at hospital admission

Meticillin-resistant Staphylococcus aureus (MRSA) is prevalent throughout the healthcare system in Spain, particularly in long-term care facilities (LTCF) and the incidence of MRSA bloodstream infection (MRSA-BSI) at hospital admission is increasing. This study aimed to determine factors that predict meticillin resistance among patients who require hospitalization for S. aureus BSI. We performed a case-control study comparing patients with S. aureus at hospital admission from January 1991 to December 2003. Case patients with MRSA-BSI at hospital admission (N=50) were compared with control patients with meticillin-susceptible S. aureus bloodstream infection (MSSA-BSI) at hospital admission (N=98). The incidence of MRSA-BSI at hospital admission increased significantly from 0.08 cases/1000 hospital admissions in 1991 to 0.37 cases in 2003 (P<0.001). Univariate analysis comparing patients with MRSA- and MSSA-BSI found a significant association between meticillin resistance and age >60 years, female sex, prior MRSA isolation and healthcare-related BSI. No differences were found in underlying conditions such as diabetes, haemodialysis, immunosuppression, source of infection or mortality between the two groups. Multivariate analyses identified prior MRSA isolation [odds ratio (OR): 41; 95% confidence interval (CI): 4-350] and admission from long-term care facilities (OR: 37; 95% CI: 4.5-316) as independent risk factors for MRSA-BSI.

Methicillin-resistant Staphylococcus aureus in critical care areas

In recent years the mainstay of treatment for hospital-associated MRSA infections has been vancomycin, but now vancomycin intermediate S aureus strains are beginning to emerge. Complete vancomycin resistant S aureus can develop, possessing the same vanA gene as vancomycin-resistant enterococcus. Four such isolates have been reported, three of which have been in the United States. There are new antibiotics being developed, but there is always a risk of resistance developing. There are some promising new ideas such as staphylococcal conjugate vaccines that reduce the rates of S aureus bacteremia for up to 10 months postimmunization in patients who have end stage renal disease receiving hemodialysis, but studies are ongoing. With all the uncertainty surrounding treatment, at least one medium has remained consistent and effective if used properly--infection control. But this requires complete support of all healthcare workers and hospital administration from the chief medical officer to doctors and nurses to environmental services personnel to take ownership of an effective infection control program. Who will advocate for more stringent infection control policies and for the equipment to successfully carry them out? Who will take the lead by ensuring implementation of infection control policies on a unit is effective? Who will hold themselves and other health care workers including physicians accountable to comply with these infection control policies every time they enter a patient's room? Nurses are on the front lines in the battle against antibiotic-resistant nosocomial infections such as MRSA, and we should not be apathetic or feel we are helpless. It is our duty as patient advocates not to take a spectator role but to answer these questions: "I will."

Vancomycin in vitro bactericidal activity and its relationship to efficacy in clearance of methicillin-resistant Staphylococcus aureus bacteremia

We examined the relationship between the time to clearance of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia while patients were receiving vancomycin therapy and the in vitro bactericidal activity of vancomycin. Vancomycin killing assays were performed with 34 MRSA bloodstream isolates (17 accessory gene regulator group II [agr-II] and 17 non-agr-II isolates) from 34 different patients with MRSA bacteremia for whom clinical and microbiological outcomes data were available. Vancomycin doses were prospectively adjusted to achieve peak plasma concentrations of 28 to 32 mug/ml and trough concentrations of 8 to 12 microg/ml. Bactericidal assays were performed over 24 h with approximately 10(7) to 10(8) CFU/ml in broth containing 16 microg/ml vancomycin. The median time to clearance of bacteremia was 6.5 days for patients with MRSA isolates demonstrating > or =2.5 reductions in log(10) CFU/ml at 24 h and >10.5 days for patients with MRSA isolates demonstrating <2.5 log(10) CFU/ml by 24 h (P = 0.025). The median time to clearance was significantly longer with MRSA isolates with vancomycin MICs of 2.0 microg/ml compared to that with MRSA isolates with MICs of < or =1.0 microg/ml (P = 0.019). The bacteremia caused by MRSA isolates with absent or severely reduced delta-hemolysin expression was of a longer duration of bacteremia (10 days and 6.5 days, respectively; P = 0.27) and had a decreased probability of eradication (44% and 78%, respectively; P = 0.086). We conclude that strain-specific microbiological features of MRSA, such as increased vancomycin MICs and decreased killing by vancomycin, appear to be predictive of prolonged MRSA bacteremia while patients are receiving vancomycin therapy. Prolonged bacteremia and decreased delta-hemolysin expression may also be related. Evaluation of these properties may be useful in the consideration of antimicrobial therapies that can be used as alternatives to vancomycin for the treatment of MRSA bacteremia.

Multidrug-resistant Acinetobacter infection mortality rate and length of hospitalization

Acinetobacter infections have increased and gained attention because of the organism’s prolonged environmental survival and propensity to develop antimicrobial drug resistance. The effect of multidrug-resistant (MDR) Acinetobacter infection on clinical outcomes has not been reported. A retrospective, matched cohort investigation was performed at 2 Baltimore hospitals to examine outcomes of patients with MDR Acinetobacter infection compared with patients with susceptible Acinetobacter infections and patients without Acinetobacter infections. Multivariable analysis controlling for severity of illness and underlying disease identified an independent association between patients with MDR Acinetobacter infection (n = 96) and increased hospital and intensive care unit length of stay compared with 91 patients with susceptible Acinetobacter infection (odds ratio [OR] 2.5, 95% confidence interval [CI] 1.2–5.2 and OR 2.1, 95% CI 1.0–4.3] respectively) and 89 uninfected patients (OR 2.5, 95% CI 1.2–5.4 and OR 4.2, 95% CI 1.5–11.6] respectively). Increased hospitalization associated with MDR Acinetobacter infection emphasizes the need for infection control strategies to prevent cross-transmission in healthcare settings.

Costs of an outbreak of meticillin-resistant Staphylococcus aureus

An outbreak of meticillin-resistant Staphylococcus aureus (MRSA) occurred in surgical and internal medicine units of a 1752-bed Finnish tertiary care hospital during 2003-2004. In order to analyse the costs of this 14-month outbreak, patients were categorized as follows: patients with MRSA infections; patients with MRSA colonization; patients exposed to MRSA but whose MRSA status remained inconclusive; and exposed patients who were negative for MRSA. We reviewed a sample of patients' charts to determine the types of clinical infections and interviewed staff about the practical implementation of control measures. The number of patients and patient-days involved in the outbreak were identified from the hospital's databases, with the administrative database supplying unit costs of work and materials. Loss of income due to closed beds was analysed. A total of 266 MRSA-positive patients (114 with infections and 152 colonized) and 797 patients exposed to MRSA were identified (11,744 contact isolation days). There were 1240 patients negative after screening (9880 contact isolation days). Total additional costs of MRSA were 386,062 euro (70% for screening and 25% for contact isolation). Costs due to meticillin resistance in treatment of MRSA infections were 16,000 euro. The income loss for this hospital due to closed beds was 1,183,808 euro. The high cost of MRSA screening underlines the importance of appropriate screening methods. Our model of analysing costs might be useful for other hospitals after adapting variables such as local control measures.

An effective computerized reminder for contact isolation of patients colonized or infected with resistant organisms

PURPOSE

To improve contact isolation rates among patients admitted to the hospital with a known history of infection with Methicillin-resistant Staphylococcus aureus (MRSA) and Vancomycin-resistant Enterococci (VRE).

METHODS

A before and after interventional study implementing computerized reminders for contact isolation between February 25, 2005 and February 28, 2006. We measured rates of appropriate contact isolation, and time to isolation for the 4 month pre-intervention period, and the 12 month intervention period. We conducted a survey of ordering physicians at the midpoint of the intervention period.

RESULTS

Implementing a computerized reminder increased the rate of patients appropriately isolated from 33% to fully 89% (P<0.0001). The median time to writing contact isolation orders decreased from 16.6 to 0.0 h (P<0.0001). Physicians accepted the order 80% of the time on the first or second presentation. Ninety-five percent of physicians felt the reminder had no impact on workflow, or saved them time.

CONCLUSION

A human reviewed computerized reminder can achieve high rates of compliance with infection control recommendations for contact isolation, and dramatically reduce the time to orders being written upon admission.

Clinical impact of MRSA in a stem cell transplant unit: analysis before, during and after an MRSA outbreak

Meticillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen, with an increased incidence in the UK since 1993, causing serious morbidity and mortality in immunosuppressed patients. We analysed the frequency and outcome of MRSA infection in a single-centre transplant population over a 5-year period. The total number of patients infected was 41/776 (5%). The frequency in autologous, sibling and unrelated donor transplants was 3, 6 and 9%, respectively. Prior to 2004, the incidence was <4%/year; however, an outbreak in the day unit resulted in 22 patients becoming newly infected. Over 90% of infections were clinically relevant, half (49%) being bacteraemia. Three patterns were seen: known MRSA positive at any time before transplant (n=15), MRSA first detected during the neutropenia phase (n=5) and MRSA only post discharge (n=21). MRSA was implicated in a number of deaths, at all time points, in those infected. An intensive eradication policy resulted in new infections dropping to <2%. In conclusion, MRSA is likely to remain endemic in our unit, but robust early screening protocols and aggressive eradication strategies have effectively limited the spread of and morbidity due to this pathogen.

Abdominal ultrasound in the intensive care unit: a 3-year survey on 400 patients

OBJECTIVE

This study analyzed 400 ultrasound examinations in the ICU to assess the indications of this imaging modality.

DESIGN AND SETTING

Retrospective analysis on prospectively collected data on 400 patients in a tertiary care hospital.

PATIENTS AND PARTICIPANTS

The observational, prospective, clinical study examined 400 bedside abdominal ultrasound examinations performed in the ICU, of which 2% were performed emergently, 56% urgently, and 42% electively.

MEASUREMENTS AND RESULTS

Environmental conditions impaired the examination slightly in 54%, moderately in 27%, and severely in 4%. Total time per study ranged from 1 to 45 min (median 10). New pathological findings were detected in 31% while 33% confirmed already known pathologies. In 53% there was no therapeutic consequence, in 27% treatment was continued based on the sonographic findings, in 10% an intervention was necessary, in 6% other therapeutic changes followed, and in 4% additional evaluation was deemed necessary. In 80% no other imaging test had to be performed.

CONCLUSIONS

Ultrasound studies are deemed sufficient in a large proportion of patients and help to avoid other, more elaborate imaging studies. However, more focused indications for studies may help to improve cost-effectiveness.

Controlled evaluation of the IDI-MRSA assay for detection of colonization by methicillin-resistant Staphylococcus aureus in diverse mucocutaneous specimens

Rapid and reliable detection of methicillin-resistant Staphylococcus aureus (MRSA) carriers is crucial for the effective control of MRSA transmission in healthcare facilities. The aim of this study was to verify the performance of the IDI-MRSA real-time PCR assay for direct MRSA detection in diverse mucocutaneous swabs from hospitalized patients. Swabs from nares (n = 522) and skin or other superficial sites (n = 478) were prospectively collected for MRSA screening from 466 patients admitted to an 858-bed teaching hospital. Swabs were inoculated onto selective chromogenic MRSA-ID agar, buffer extraction solution for IDI-MRSA assay, and enrichment broth. MRSA was detected by culture in 100 specimens from 47 patients. Compared to enrichment culture, the sensitivity and specificity of the PCR assay were 81.0 and 97.0%, respectively, and its positive and negative predictive values were 75.0 and 97.9%, respectively. The IDI-MRSA assay was more sensitive on swabs from nares (90.6%) than from other body sites (76.5%, P < 0.01). The PCR assay detected MRSA in 42 of 47 patients with culture positive study samples. Of 26 patients with culture-negative but PCR-positive study samples, 11 were probable true MRSA carriers based on patient history and/or positive culture on a new sample. The median turnaround time for PCR results was 19 h versus 3 days for agar culture results and 6 days for enrichment culture results. These data confirm the value of IDI-MRSA assay for rapid screening of MRSA mucocutaneous carriage among hospitalized patients. Cost-effectiveness studies are warranted to evaluate the impact of this assay on infection control procedures in healthcare settings.

Emerging Options for Treatment of Invasive, Multidrug-ResistantStaphylococcus aureusInfections

Limited established treatment options exist for the treatment of serious, invasive infections caused by multidrug-resistant Staphylococcus aureus, most notably nosocomially acquired methicillin-resistant S. aureus (MRSA). Although vancomycin represents the gold standard for therapy of such invasive infections, reports of increasing in vitro resistance to vancomycin, combined with reports of clinical failures (with this and other antistaphylococcal agents), underscore the need for alternative therapies. Older agents with favorable in vitro activity available in both oral and intravenous dose forms include trimethoprim-sulfamethoxazole and clindamycin. Limited clinical data exist to support their routine use as initial therapy in the treatment of invasive disease. However, these and other options (e.g., tetracyclines) are being reexplored in the setting of increasing concern over MRSA acquired in the community setting. Newer treatment options for MRSA include linezolid, quinupristin-dalfopristin, daptomycin, and tigecycline. With the exception of linezolid, these newer agents require intravenous administration. Combination therapy may be considered in select invasive diseases refractory to standard monotherapies. These diseases include infections such as endocarditis, meningitis, and prosthetic device infections. Additional alternatives to vancomycin are under clinical investigation. Those in later stages of development include oritavancin, dalbavancin, telavancin, and ceftobiprole.

Cost of Gram-negative resistance*

OBJECTIVE

It is unclear that infections with Gram-negative rods resistant to at least one major class of antibiotics (rGNR) have a greater effect on patient morbidity than infections caused by sensitive strains (sGNR). We wished to test the hypothesis that rGNR infections are associated with higher resource utilization.

DESIGN

Retrospective observational cohort study of prospectively collected data.

SETTING

University hospital surgical intensive care unit and ward.

PATIENTS

Surgical patients with at least one GNR infection.

MEASUREMENTS

We compared admissions treated for rGNR infection with those with sGNR infections. Primary outcomes were total hospital costs and hospital length of stay. Other outcomes included antibiotic treatment cost, in-hospital death, and intensive care unit length of stay. After univariate analysis comparing outcomes after rGNR infection with those after sGNR infection, multivariate linear regression models for hospital cost and length of stay were created to account for potential confounders.

MAIN RESULTS

Cost data were available for 604 surgical admissions treated for at least one GNR infection (Centers for Disease Control and Prevention criteria), 137 (23%) of which were rGNR infections. Admissions with rGNR infections were associated with a higher severity of illness at the time of infection (Acute Physiology and Chronic Health Evaluation II score, 17.6 +/- 0.6 vs. 13.9 +/- 0.3), had higher median hospital costs ($80,500 vs. $29,604, p < .0001) and median antibiotic costs ($2,607 vs. $758, p < .0001), and had longer median hospital length of stay (29 vs. 13 days, p < .0001) and median intensive care unit length of stay (13 days vs. 1 day, p < .0001). Infection with rGNR within the first 7 days of admission was independently predictive of increased hospital cost (incremental increase in median hospital cost estimated at $11,075; 95% confidence interval, $3,282-$20,099).

CONCLUSIONS

Early infection with rGNR is associated with a high economic burden, which is in part related to increased antibiotic utilization compared with infection with sensitive organisms. Efforts to control overuse of antibiotics should be pursued.

Clinical, epidemiological, and laboratory aspects of methicillin-resistant Staphylococcus aureus (MRSA) infections

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen responsible for both hospital- and community-onset disease. Resistance to methicillin in S. aureus is mediated by PBP2a, a penicillin-binding protein with low affinity to beta-lactams, encoded by the mecA gene. Accurate susceptibility testing of S. aureus isolates and screening of patients for colonization with MRSA are important tools to limit the spread of this organism. This review focuses on the clinical significance of MRSA infections and new approaches for the laboratory diagnosis and epidemiological typing of MRSA strains.

Methicillin-resistant Staphylococcus aureus: A public health issue with economic consequences

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has become endemic worldwide in hospitals, and community-associated MRSA is spreading into the community at large.

OBJECTIVES

To estimate the current cost of MRSA in Canada and to assess the magnitude of this public health issue.

METHODS

An extensive review of the literature was conducted to gather epidemiology, health care resource utilization and cost data for MRSA in Canadian settings. The current MRSA burden was estimated using available cost data and the most recent epidemiology data.

RESULTS

The rate of MRSA in Canadian hospitals increased from 0.46 to 5.90 per 1000 admissions between 1995 and 2004, while community-associated MRSA continued to spread into the community. Patients harbouring MRSA required prolonged hospitalization (average 26 days of isolation per patient), special control measures, expensive treatments and extensive surveillance. Total cost per infected MRSA patient averaged $12,216, with hospitalization being the major cost driver (81%), followed by barrier precautions (13%), antimicrobial therapy (4%) and laboratory investigations (2%). The most recent epidemiological data, combined with available cost data, suggest that direct health care cost attributable to MRSA in Canada, including cost for management of MRSA-infected and-colonized patients and MRSA infrastructure, averaged $82 million in 2004 and could reach $129 million in 2010.

CONCLUSION

MRSA is a costly public health issue that needs to be tackled if the growing burden of this disease in Canadian hospitals and in the community is to be limited.

Comparative bactericidal activities of daptomycin and vancomycin against glycopeptide-intermediate Staphylococcus aureus (GISA) and heterogeneous GISA isolates

Staphylococcus aureus strains from the U.S. SENTRY Antimicrobial Surveillance Program, 2002-2003, glycopeptide-intermediate S. aureus (GISA) strains, and heterogeneous GISA (hGISA) strains were used to compare bactericidal activities of daptomycin and vancomycin using MICs and minimum bactericidal concentrations. Glycopeptide-susceptible S. aureus and hGISA strains were further studied by using time-kill curves. For all isolates, the daptomycin MIC50 and MIC90 are four times lower and the log drops in viable counts at 6 h and 24 h are significantly greater than those for vancomycin.

Efficacy of daptomycin in complicated skin and skin-structure infections due to methicillin-sensitive and -resistant Staphylococcus aureus: results from the CORE Registry

OBJECTIVE

To characterize postmarketing clinical experience with daptomycin in treating complicated skin and skin-structure infections (cSSSIs) due to culture-confirmed MRSA and MSSA in real-life prescribing situations.

RESEARCH DESIGN AND METHODS

The Cubicin Outcomes Registry and Experience 2004 (CORE 2004) is a multicenter observational registry involving 45 separate institutions, designed to characterize infection types, pathogens, and outcomes of patients who were treated with daptomycin. A subset analysis of the CORE 2004 data was conducted to characterize patients with cSSSI due to culture-confirmed MRSA and MSSA, but without bacteremia, endocarditis, osteomyelitis, or other significant infectious processes. Clinical information, including patient demographics, antibiotic treatments, and clinical outcome, was analyzed. Adverse event data were not collected in CORE 2004.

MAIN OUTCOME MEASURE

Clinical success (cured or improved) or failure was assessed at the end of daptomycin treatment.

RESULTS

A total of 165 patients were identified, including 145 patients (87.9%) with MRSA and 20 patients (12.1%) with MSSA infections. Most patients received daptomycin at a dosage of 4-6 mg/kg intravenously and at a frequency of once every 24 h. Daptomycin dosing frequency was adjusted to once every 48 h or thrice weekly in all seven patients who had received hemodialysis. Prior antibiotic therapy had been administered to 121/163 (74.2%) patients and concomitant antibiotic therapy to 65/165 (39.4%) of patients. Clinical success was achieved with daptomycin in 89.1% of patients overall, including 89.7% and 85.0% of those with MRSA and MSSA, respectively. Among patients with a successful outcome, the total days of daptomycin therapy (median days: MRSA = 13.0, MSSA = 11.0) and the days to clinical response (median days: MRSA = 3.5, MSSA = 2.0) were not significantly different for MRSA and MSSA patients (p = 0.27 and p = 0.15 respectively, median test).

CONCLUSIONS

Given the limitations of this registry (which include its retrospective nature; limited numbers of MSSA patients; and lack of specific information on adverse events, type and duration of prior antibiotic therapy, timing and duration of concomitant antibiotic therapy, concomitant surgical interventions, and possible on-therapy dosing adjustments), daptomycin appeared effective in postmarketing clinical practice in the treatment of cSSSI caused by MRSA and MSSA.

In vitro activity of daptomycin against methicillin-resistant Staphylococcus aureus, including heterogeneously glycopeptide-resistant strains

The purpose of the present study was to assess the in vitro activity of daptomycin against a well-defined collection of methicillin-resistant Staphylococcus aureus (MRSA) isolates (n = 98), including heterogeneously glycopeptide-resistant MRSA (hGISA) strains. Susceptibility testing was performed by using the Etest system. Daptomycin was potent against both glycopeptide-susceptible and hGISA strains.

Antibacterial resistance and their genetic location in MRSA isolated in Kuwait hospitals, 1994-2004

Background

Methicillin-resistant Staphylococcus aureus (MRSA) continues to be a major cause of serious infections in hospitals and in the community worldwide. In this study, MRSA isolated from patients in Kuwait hospitals were analyzed for resistance trends and the genetic location of their resistance determinants.

Methods

Between April 1994 and December 2004, 5644 MRSA isolates obtained from different clinical samples were studied for resistance to antibacterial agents according to guidelines from the National Committee for Clinical Laboratory Standards and the British Society for Antimicrobial Chemotherapy. The genetic location of their resistance determinants was determined by curing and transfer experiments.

Results

They were resistant to aminoglycosides, erythromycin, tetracycline, trimethoprim, fusidic acid, ciprofloxacin, chloramphenicol, rifampicin, mupirocin, cadmium acetate, mercuric chloride, propamidine isethionate and ethidium bromide but susceptible to vancomycin, teicoplanin and linezolid. The proportion of the isolates resistant to erythromycin, ciprofloxacin and fusidic acid increased during the study period. In contrast, the proportion of isolates resistant to gentamicin, tetracycline, chloramphenicol and trimethoprim declined. High-level mupirocin resistance increased rapidly from 1996 to 1999 and then declined. They contained plasmids of 1.9, 2.8, 3.0, 4.4, 27 and 38 kilobases. Genetic studies revealed that they carried plasmid-borne resistance to high-level mupirocin resistance (38 kb), chloramphenicol (2.8 – 4.4 kb), erythromycin (2.8–3.0 kb) and cadmium acetate, mercuric chloride, propamidine isethionate and ethidium bromide (27 kb) and chromosomal location for methicillin, the aminoglycosides, tetracycline, fusidic acid, ciprofloxacin and trimethoprim resistance. Thus, the 27 kb plasmids had resistance phenotypes similar to plasmids reported in MRSA isolates in South East Asia.

Conclusion

The prevalence of resistance to erythromycin, ciprofloxacin, high-level mupirocin and fusidic acid increased whereas the proportion of isolates resistant to gentamicin, tetracycline, chloramphenicol and trimethoprim declined during the study period. They contained 27-kb plasmids encoding resistance to cadmium acetate, mercuric chloride, propamidine isethionate and ethidium bromide similar to plasmids isolated in MRSA from South East Asia. Molecular typing of these isolates will clarify their relationship to MRSA from South East Asia.

Evaluation of rapid screening and pre-emptive contact isolation for detecting and controlling methicillin-resistant Staphylococcus aureus in critical care: an interventional cohort study

INTRODUCTION

Rapid diagnostic tests may allow early identification of previously unknown methicillin-resistant Staphylococcus aureus (MRSA) carriers at intensive care unit (ICU) admission. The aim of this study was twofold: first, to assess whether a new molecular MRSA screening test can substantially decrease the time between ICU admission and identification of MRSA carriers; and, second, to examine the combined effect of rapid testing and pre-emptive contact isolation on MRSA infections.

METHOD

Since November 2003, patients admitted for longer than 24 hours to two adult ICUs were screened systematically on admission using quick, multiplex immunocapture-coupled PCR (qMRSA). Median time intervals from admission to notification of test results were calculated for a five-month intervention phase (November 2003-March 2004) and compared with a historical control period (April 2003-October 2003) by nonparametric tests. ICU-acquired MRSA infection rates were determined for an extended surveillance period (January 2003 through August 2005) and analyzed by Poisson regression methods.

RESULTS

During the intervention phase, 97% (450/462) of patients admitted to the surgical ICU and 80% (470/591) of patients admitted to the medical ICU were screened. On-admission screening identified the prevalence of MRSA to be 6.7% (71/1053). Without admission screening, 55 previously unknown MRSA carriers would have been missed in both ICUs. Median time from ICU admission to notification of test results decreased from 87 to 21 hours in the surgical ICU (P < 0.001) and from 106 to 23 hours in the medical ICU (P < 0.001). In the surgical ICU, 1,227 pre-emptive isolation days for 245 MRSA-negative patients were saved by using the qMRSA test. After adjusting for colonization pressure, the systematic on-admission screening and pre-emptive isolation policy was associated with a reduction in medical ICU acquired MRSA infections (relative risk 0.3, 95% confidence interval 0.1-0.7) but had no effect in the surgical ICU (relative risk 1.0, 95% confidence interval 0.6-1.7).

CONCLUSION

The qMRSA test decreased median time to notification from four days to one day and helped to identify previously unknown MRSA carriers rapidly. A strategy linking the rapid screening test to pre-emptive isolation and cohorting of MRSA patients substantially reduced MRSA cross-infections in the medical but not in the surgical ICU.