Diagnosis and management of methicillin resistant Staphylococcus aureus infection

Activated mesenchymal stem cells increase drug susceptibility of methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa

Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa are major causes of hospital-acquired infections and sepsis. Due to increasing antibiotic resistance, new treatments are needed. Mesenchymal stem cells (MSCs) have antimicrobial effects, which can be enhanced by preconditioning with antibiotics. This study investigated using antibiotics to strengthen MSCs against MRSA and P. aeruginosa. MSCs were preconditioned with linezolid, vancomycin, meropenem, or cephalosporin. Optimal antibiotic concentrations were determined by assessing MSC survival. Antimicrobial effects were measured by minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and antimicrobial peptide (AMP) gene expression. Optimal antibiotic concentrations for preconditioning MSCs without reducing viability were 1 μg/mL for linezolid, meropenem, and cephalosporin and 2 μg/mL for vancomycin. In MIC assays, MSCs preconditioned with linezolid, vancomycin, meropenem, or cephalosporin inhibited MRSA or P. aeruginosa growth at lower concentrations than non-preconditioned MSCs (p ≤ 0.001). In MBC assays, preconditioned MSCs showed enhanced bacterial clearance compared to non-preconditioned MSCs, especially when linezolid and vancomycin were used against MRSA (p ≤ 0.05). Preconditioned MSCs showed increased expression of genes encoding the antimicrobial peptide genes hepcidin and LL-37 compared to non-preconditioned MSCs. The highest hepcidin expression was seen with linezolid and vancomycin preconditioning (p ≤ 0.001). The highest LL-37 expression was with linezolid preconditioning (p ≤ 0.001). MSCs' preconditioning with linezolid, vancomycin, meropenem, or cephalosporin at optimal concentrations enhances their antimicrobial effects against MRSA and P. aeruginosa without compromising viability. This suggests preconditioned MSCs could be an effective adjuvant treatment for antibiotic-resistant infections. The mechanism may involve upregulation of AMP genes.

In vitro selection of single-stranded DNA molecular recognition elements against S. aureus alpha toxin and sensitive detection in human serum

Alpha toxin is one of the major virulence factors secreted by Staphylococcus aureus, a bacterium that is responsible for a wide variety of infections in both community and hospital settings. Due to the prevalence of S. aureus related infections and the emergence of methicillin-resistant S. aureus, rapid and accurate diagnosis of S. aureus infections is crucial in benefiting patient health outcomes. In this study, a rigorous Systematic Evolution of Ligands by Exponential Enrichment (SELEX) variant previously developed by our laboratory was utilized to select a single-stranded DNA molecular recognition element (MRE) targeting alpha toxin with high affinity and specificity. At the end of the 12-round selection, the selected MRE had an equilibrium dissociation constant (K_d) of 93.7 ± 7.0 nM. Additionally, a modified sandwich enzyme-linked immunosorbent assay (ELISA) was developed by using the selected ssDNA MRE as the toxin-capturing element and a sensitive detection of 200 nM alpha toxin in undiluted human serum samples was achieved.

Therapeutic effect of photodynamic therapy using Na-pheophorbide a on osteomyelitis models in rats

OBJECTIVE

In this study, we examined the therapeutic effect of photodynamic therapy (PDT) using the photosensitizer Na-Pheophorbide a (Na-Phde a) on osteomyelitis models in rats.

BACKGROUND

Osteomyelitis is one of the most serious infectious problems in the orthopedic field. Recently, as a new clinical approach against septic arthritis, an experimental in vivo and in vitro model for the inactivation of methicillin-resistant-Staphylococcus aureus by PDT using Na-Phde a has been developed.

METHODS

Methicillin-sensitive Staphylococcus aureus (MSSA) was injected into the tibia of the rats to create osteomyelitis models (n = 10, 10 legs). A total of 560 μmol/l of Na-Phde a solution was injected into five of these tibial osteomyelitis models (five legs) 48 h after the initial MSSA infection. Sixty minutes after the Na-Phde a injection, a semiconductor laser (125 mW, 670 nm) was used to irradiate the models for 10 min with a total energy of 93.8 J/mm(2). As a control group, five rats (five legs) were treated with a phosphate buffered saline injection at 48 h after MSSA infection. Weight and leg perimeter changes were plotted. Bacterial growth, histological examination and radiological examination were evaluated at 14 days after initial treatment.

RESULTS

PDT with Na-Phde a significantly prevented leg swelling. In the PDT group, bone destruction owing to osteomyelitis was inhibited not only histologically but also radiographically.

CONCLUSIONS

The results in these experiments show that PDT using Na-Phde a improved osteomyelitis in rats. This suggests that PDT using Na- Phde a can be a useful treatment for osteomyelitis.

Bactericidal effect of photodynamic therapy using Na-pheophorbide a: evaluation of adequate light source

OBJECTIVE

To evaluate the efficacy of photodynamic therapy (PDT) against methicillin resistant-Staphylococcus aureus (MRSA) by selecting different light sources for irradiation and combining them with the photosensitizer Na-Pheophorbide a (Na-Phde a).

BACKGROUND

The treatment of drug-resistant bacterial infection is a serious issue. Recently, as a new clinical approach against septic arthritis, an experimental in vivo and in vitro model for the inactivation of MRSA by PDT using the photosensitizer Na-Phde a has been developed.

MATERIALS AND METHODS

Na-Phde a solution (280 micromol/L) was mixed with MRSA strain bacterial inoculum. After 60 minutes, light was irradiated for 30 minutes using the following light sources: GaA1p semiconductor laser (300 mW, 670 nm), halogen lamp (75 W), xenon lamp (300 W) and fluorescent lamp (27 W). Bacterial growth was evaluated after 24 hours incubation in a blood agar culture.

RESULTS

The semiconductor laser and halogen lamp groups showed perfect bactericidal effects after PDT. The xenon lamp and fluorescent lamp groups showed partial bactericidal effects.

CONCLUSIONS

The results of this experiment showed that PDT using the combination of Na-Phde a with a semiconductor laser or halogen lamp showed a better bactericidal performance than with xenon or fluorescent lamps. These findings indicated that PDT using Na-Phde a could be a useful treatment for septic arthritis and soft tissue infection.

In vivo assessment of the antimicrobial activity of a calcium-deficient apatite vancomycin drug delivery system in a methicillin-resistant Staphylococcus aureus rabbit osteomyelitis experimental model

The antimicrobial activities of calcium-deficient apatite loaded with different concentrations (25, 100, and 500 microg/mg) of vancomycin as a filling biomaterial were evaluated in a methicillin-resistant Staphylococcus aureus (MRSA) rabbit acute osteomyelitis model. Bacterial counts in bone, bone marrow, and joint fluid samples treated with forms of the apatite were compared to those in tissue samples receiving a constant intravenous vancomycin infusion after 4 days. This study demonstrates that using a calcium-deficient apatite loaded with vancomycin dramatically decreases the bacterial counts in bone and marrow.

The minimum influences for murine normal joint tissue by novel bactericidal treatment and photodynamic therapy using na-pheophorbide a for septic arthritis

OBJECTIVE

In this study, we examined the effect of photodynamic therapy (PDT) using Na-pheophorbide a (Na-Phde a) on normal joint tissue.

BACKGROUND DATA

The treatment of methicillin-resistant Staphylococcus aureus (MRSA) infection is a serious issue. Recently, an experimental in vivo and in vitro model for the inactivation of MRSA by PDT using a photosensitizer, Na-Phde a, has been developed.

MATERIALS AND METHODS

The knee joints of mice were injected with 560 or 280 micromol/L of Na-Phde a. Thirty minutes after injection, percutaneous laser irradiation was applied for 5 min using a semiconductor laser (power: 125 mW; wavelength: 664 nm; total energy: 12 J/cm2). The joint perimeter and body weight of the treated mice were monitored, and histological evaluation was also done.

RESULTS

Joint swelling was observed up to 3 wk after PDT (p < 0.05). On histology 1 wk post-PDT, the treated knees were found to have inflammatory changes, primarily in synovial tissue. Eight weeks after PDT, the synovitis was no longer present. No significant effects were observed on cartilage, bone marrow, or menisci.

CONCLUSIONS

The results of this experiment showed that PDT with Na-Phde a induced arthritis for a short time after treatment. However, this arthritis was reversible, and the PDT did not appear to induce osteoarthritic changes in normal joint tissue. These findings indicate that PDT using Na-Phde a caused minimal but reversible changes in joint tissue, suggesting that it would be a safe and useful treatment for bacterial septic arthritis.

Infection of surgical wounds in the maxillofacial region and free flap donor sites with methicillin-resistant Staphylococcus aureus

We studied the acquisition of methicillin-resistant Staphylococcus aureus (MRSA) in two groups of patients who had free flap reconstructions of defects after excision of lesions in the head and neck. The first group (n=31) was given a 5-day perioperative course of antibiotic prophylaxis (long-term) and the second (n=33) a 24-h course (short-term). MRSA was the main infecting organism. Seventeen of the 64 patients (27%) developed an infection with MRSA, including seven at donor sites of free flaps. All infections were acquired after operation, and delayed healing or discharge in five patients with MRSA and four with infections with other organisms. The median length of hospital admission was greater for patients that acquired MRSA (p=0.005). There were significantly fewer patients with wounds infected by MRSA in the short-term group (4/33 compared with 13/31, p=0.01). We recommend the short-term use of an antibiotic for surgical prophylaxis and the application of cross-infection control measures on the ward.

Antibiotic resistance as a global threat: evidence from China, Kuwait and the United States

Background

Antimicrobial resistance is an under-appreciated threat to public health in nations around the globe. With globalization booming, it is important to understand international patterns of resistance. If countries already experience similar patterns of resistance, it may be too late to worry about international spread. If large countries or groups of countries that are likely to leap ahead in their integration with the rest of the world – China being the standout case – have high and distinctive patterns of resistance, then a coordinated response could substantially help to control the spread of resistance. The literature to date provides only limited evidence on these issues.

Methods

We study the recent patterns of antibiotic resistance in three geographically separated, and culturally and economically distinct countries – China, Kuwait and the United States – to gauge the range and depth of this global health threat, and its potential for growth as globalization expands. Our primary measures are the prevalence of resistance of specific bacteria to specific antibiotics. We also propose and illustrate methods for aggregating specific "bug-drug" data. We use these aggregate measures to summarize the resistance pattern for each country and to study the extent of correlation between countries' patterns of drug resistance.

Results

We find that China has the highest level of antibiotic resistance, followed by Kuwait and the U.S. In a study of resistance patterns of several most common bacteria in China in 1999 and 2001, the mean prevalence of resistance among hospital-acquired infections was as high as 41% (with a range from 23% to 77%) and that among community- acquired infections was 26% (with a range from 15% to 39%). China also has the most rapid growth rate of resistance (22% average growth in a study spanning 1994 to 2000). Kuwait is second (17% average growth in a period from 1999 to 2003), and the U.S. the lowest (6% from 1999 to 2002). Patterns of resistance across the three countries are not highly correlated; the most correlated were China and Kuwait, followed by Kuwait and the U.S., and the least correlated pair was China and the U.S.

Conclusion

Antimicrobial resistance is a serious and growing problem in all three countries. To date, there is not strong international convergence in the countries' resistance patterns. This finding may change with the greater international travel that will accompany globalization. Future research on the determinants of drug resistance patterns, and their international convergence or divergence, should be a priority.

Methicillin-resistant Staphylococcus aureus: clinical manifestations and antimicrobial therapy

Methicillin-resistant Staphylococcus aureus (MRSA) is a common skin coloniser and less commonly causes infection. MRSA colonisation should be contained by infection control measures and not treated. MRSA infections cause the same spectrum of infection as MSSA infections, i.e., skin/soft tissue infections, bone/joint infections, central IV line infections, and acute bacterial endocarditis (native valve/prosthetic valve). There is a discrepancy between in-vitro sensitivity and in-vivo effectiveness with MRSA. To treat MRSA infections, clinicians should select an MRSA drug with proven in-vivo effectiveness, i.e., daptomycin. Linezolid, quinupristin/dalfopristin, minocycline, or vancomycin, and not rely on in-vitro susceptibility data. For MRSA, doxycycline cannot be substituted for minocycline. Linezolid and minocycline are available for oral administration and both are also effective in treating MRSA CNS infections. Vancomycin is being used less due to side effects, (increasing MICs/resistance, VISA/VRSA), and increased VRE prevalence. The most potent anti-MRSA drug at the present time is daptomycin. Daptomycin is useful when rapid/effective therapy of MRSA bacteraemia/endocarditis is necessary. Daptomycin is also useful to treat persistent MRSA bacteraemias/MRSA treatment failures with other drugs, i.e., vancomycin. There is no difference in virulence between MSSA and MRSA infections if treatment is started early and with an agent that has in-vivo effectiveness.

Skin necrosis of a pectoralis major myocutaneous flap, caused by methicillin-resistant Staphylococcus aureus

A case of MRSA-induced skin necrosis of part of a pectoralis muscle flap is described. It highlights the importance of recognising potential MRSA infection following surgery and treating it early and aggressively.

Strain relatedness of endemic MRSA isolates in a burns unit in South India--a five year study

Methicillin-resistant Staphylococcus aureus (MRSA) is an important hospital-acquired pathogen in healthcare centres worldwide. The strain characteristics vary widely from country to country, although some strains have the propensity to spread globally. E-MRSA 15 and 16 have been established as epidemic strains in the UK and Europe. MRSA is widely prevalent in the Indian sub-continent and is endemic in the Burns Unit of St Johns Medical College Hospital, Bangalore, India. The purpose of the study was to investigate the predominance of one or more epidemic strains within an endemic situation. A representative selection of 65 isolates of MRSA over a period spanning five years (1994-1998) was subjected to antibiogram comparison, phage-typing and pulsed field gel electrophoresis (PFGE) using SmaI. The antibiogram comparison was not a discerning method of strain discrimination. At least 11 different phage-types were seen among these 65 isolates; 35.4% belonged to phage-types A and SM-A. PFGE studies showed 12 distinct patterns, with a single pattern accounting for over half of the isolates. The study showed that the isolates from India were diverse and distinct from strains of MRSA such as E-MRSA reported from many studies in the UK. Molecular characterization of isolates is a source of valuable information that could enhance global surveillance; more work is needed across the Indian sub-continent to establish the nature of MRSA strain diversity.

Detection of methicillin and mupirocin resistance in Staphylococcus aureus isolates using conventional and molecular methods: a descriptive study from a burns unit with high prevalence of MRSA

AIMS

To compare conventional phenotypic methods for the detection of methicillin and mupirocin resistance in Staphylococcus aureus in routine laboratory practice with reference to an established molecular method.

METHODS

This study was conducted on a selection of 65 isolates of methicillin resistant Staphylococcus aureus (MRSA) from a burns unit in India which is endemic for MRSA. The Kirby-Bauer and modified Stokes disc diffusion tests and the Vitek breakpoint minimum inhibitory concentration (MIC) were performed on all isolates using the presence of the mecA gene as the reference standard. Gel based and colorimetric polymerase chain reaction (PCR) assays were evaluated as molecular methods for the diagnosis of MRSA. A commercial latex agglutination test, the Mastalex, was assessed for the detection of penicillin binding protein 2a (PBP2a), the mecA gene product. Conventional disc diffusion and molecular methods were investigated for the detection of mupirocin resistance.

RESULTS

Fifty one of 65 isolates were positive for the mecA gene. All three phenotypic methods showed high sensitivity (> 96.2%), whereas the specificity varied: 50% for Kirby-Bauer, 87.5% for modified Stokes, and 93.3% for Vitek. The colorimetric PCR was less cumbersome than the gel based PCR; there was complete concordance between both systems. The Mastalex kit showed good correlation with PCR. One isolate was found to be mupirocin resistant and harboured the mupA gene.

CONCLUSIONS

The specificity of routine laboratory tests for MRSA detection was variable. mecA gene detection, the "gold standard" to confirm ambiguous results, is difficult to perform in routine diagnostic laboratories. The Mastalex kit for the detection of PBP2a is an alternative that could be used in most laboratories. High level mupirocin resistance can be confirmed with genotypic methods.

Rapid healing of MRSA infection at the suprafascial radial donor site

Methicillin-resistant Staphylococcus aureus (MRSA) infection at the radial suprafascial donor site resulted in significant loss of the skin graft, but no tendon exposure, in two patients. The complication was successfully managed with wound debridement, appropriate antibiotics, a negative-pressure wound dressing and early partial-thickness skin grafting. The suprafascial dissection creates a donor site that resists both skin graft loss and tendon exposure. It also allows early re-grafting with no loss of function in the event of skin graft loss from infection. These advantages have not been described previously.

Continuous versus intermittent infusion of vancomycin in severe Staphylococcal infections: prospective multicenter randomized study

A continuous infusion of vancomycin (CIV) may provide an alternative mode of infusion in severe hospital-acquired methicillin-resistant staphylococcal (MRS) infections. A multicenter, prospective, randomized study was designed to compare CIV (targeted plateau drug serum concentrations of 20 to 25 mg/liter) and intermittent infusions of vancomycin (IIV; targeted trough drug serum concentrations of 10 to 15 mg/liter) in 119 critically ill patients with MRS infections (bacteremic infections, 35%; pneumonia, 45%). Microbiological and clinical outcomes, safety, pharmacokinetics, ease of treatment adjustment, and cost were compared. Microbiological and clinical outcomes and safety were similar. CIV patients reached the targeted concentrations faster (36 +/- 31 versus 51 +/- 39 h, P = 0.029) and fewer samples were required for treatment monitoring than with IIV patients (7.7 +/- 2.2 versus 11.8 +/- 3.9 per treatment, P < 0.0001). The variability between patients in both the area under the serum concentration-time curve (AUC(24h)) and the daily dose given over 10 days of treatment was lower with CIV than with IIV (variances, 14,621 versus 53,975 mg(2)/liter(2)/h(2) [P = 0.026] and 414 versus 818 g(2) [P = 0.057], respectively). The 10-day treatment cost per patient was $454 +/- 137 in the IIV group and was 23% lower in the CIV group ($321 +/- 81: P < 0.0001). In summary, for comparable efficacy and tolerance, CIV may be a cost-effective alternative to IIV.

Long-term MRSA carriage in hospital patients

A retrospective study was performed to determine the frequency of and risk factors for long-term carriage of methicillin-resistant Staphylococcus aureus amongst 79 patients who initially acquired MRSA during hospital admission and were re-admitted at least once during the study period (28 months in total). Of the 52 patients who were re-screened during their re-admissions, 33 (63%) had positive MRSA screens on at least one re-screening and 19 (37%) had all negative screens. Patients whose case notes had been tagged were more likely to have screens performed. Of the potential risk factors assessed, only the presence of skin lesions significantly increased the risk of prolonged MRSA carriage (P = 0.032). Evaluation of the effect of anti-MRSA eradication treatment showed that patients who were subsequently MRSA negative on all re-admissions were more likely to have received some form of anti-MRSA treatment than those who remained positive on at least one re-admission (P = 0.048). The results show that the strain of MRSA at our hospitals (predominantly EMRSA 15) is associated with prolonged carriage in certain patients and that attempts at eradication often do not affect the duration of carriage. This has infection control implications for the management of known MRSA positive patients re-admitted to hospital.

Vancomycin treatment failures in Staphylococcus aureus lower respiratory tract infections

We reviewed all patients with Staphylococcus aureus lower respiratory tract infections treated with vancomycin at our institution in 1998, to see how this antimicrobial is performing. We found that approximately 40% of evaluable patients were considered treatment failures, even though the S. aureus was still reported as being susceptible to vancomycin. We report in detail two example patients that failed to respond clinically to vancomycin and summarize the clinical characteristics of the 23 additional patients that failed. The first case was treated four times in the intensive care unit with vancomycin. Each course, after approximately 14 days therapy, the vancomycin was discontinued and his infection relapsed soon thereafter. The second was treated with vancomycin for 10 days initially. She relapsed, was restarted on vancomycin once more, but her condition deteriorated, and she died of refractory sepsis 20 days after admission. The cost of care for each patient ranged from $50,000 to over $100,000. With trends such as these, alternative therapies are needed to control resistant Gram-positive infections.

Assessment of infection in diabetic foot ulcers

Typical signs of infection in diabetic foot ulcers are often absent or late. This literature review outlines the factors practitioners must take into account when assessing for and managing such infections.

Does MRSA affect patient outcomes in the elderly? A retrospective pilot study

We retrospectively studied admissions to our geriatric acute assessment and rehabilitation ward over a one-year period, to identify those with Methicillin-resistant Staphylococcus aureus (MRSA) and determine whether this affected outcomes. Two hundred and thirty eight admissions of 204 patients were analysed and 9.8% of patients were MRSA positive. Demographics did not differ between MRSA positive and negative patients. Respiratory co-morbidity was more common in MRSA positive patients. Rates of functional decline did not differ between the two groups. Those colonized or infected by MRSA had a significantly longer stay (51.4 vs. 32.2 days, P=0.03), perhaps due to isolation and limited rehabilitation. The virulence of MRSA may be less in these patients, therefore isolation may be inappropriate and counter-productive.

The evaluation of a cadexomer iodine wound dressing on methicillin resistant Staphylococcus aureus (MRSA) in acute wounds

BACKGROUND

Many bacteria have become resistant to commonly-used antibiotics.

OBJECTIVE

The purpose of this study was to examine the effect of a cadexomer iodine wound dressing on methicillin resistant Staphylococcus aureus (MRSA).

METHOD

Partial thickness wounds were made on the backs of three pigs and inoculated with a known amount of MRSA. Wounds were treated with either cadexomer iodine dressing or vehicle dressing (without iodine), or they were left untreated. Three wounds from each treatment group per animal were cultured using quantitative scrub techniques after 24, 48, or 72 hours of treatment.

CONCLUSIONS

The cadexomer iodine dressing significantly reduced MRSA and total bacteria in the wounds as compared to both the no treatment control and vehicle. No significant differences were observed in the number of bacteria recovered between the no treatment control and cadexomer (vehicle) treated wounds. Cadexomer iodine may be an effective agent for preventing proliferation of MRSA in wounds.

Methicillin-resistant Staphylococcus aureus infections in 11 dogs

Methicillin-resistant Staphylococcus aureus infection was identified in 11 dogs. The infection was associated with surgical treatment especially orthopaedic surgery. Infection after traumatic wounding, and recurrent pyoderma was also seen. Oral antibiotic treatment improved or resolved the infection in nine of the 11 dogs, although the methicillin-resistant isolates were susceptible to relatively few antibiotics.

Targeting lurking pathogens in acute traumatic and chronic wounds

The appropriate antimicrobial treatment for skin and soft tissue following acute trauma is determined by the mechanism of injury, time from injury to treatment, environmental wound contamination, pathogenicity of colonizing bacteria, and patient-specific issues. These factors can be used to predict the risk of secondary infection of wounds. Although common skin pathogens (such as Staphylococcus aureus and group A Streptococcus) cause most secondary wound infections, antibiotic therapy sometimes must be directed against unusual pathogens that are associated with atypical wounds, such as animal bites (amoxicillin with clavulanate for Pasteurella multocida) and plantar puncture wounds (ciprofloxacin for Pseudomonas aeruginosa). This customized treatment approach is also appropriate for chronic wounds, such as pressure and diabetic foot ulcers. In addition to antibiotic therapy, wound management may include surgical debridement. Active areas of investigation in wound management include the use of growth factors and hyperbaric oxygen.

An outbreak of methicillin-resistant staphylococcus aureus (MRSA) in a dermatology day-care unit

We describe an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) in a dermatology day-care unit and the methods used to determine the mechanism of spread and control it. The epidemic strain had a characteristic sensitivity pattern and was typeable with phages 29, 80, 95, 47, 54 and 77, which was of considerable value in interpreting the epidemiological data. The method of spread was studied by examination of the medical and nursing records of patients who had acquired MRSA (to determine which members of staff they had encountered and which other MRSA-positive patients had been present in the department at the same time) and by the microbiological screening of all patients and staff. However, screening of all staff by nasal swabbing failed to identify carriage of the epidemic strain, while extensive swabbing of surfaces on the day-care unit also failed to show any evidence of MRSA in the environment. This suggests that the MRSA was most probably spread from patient to patient via the hands of staff, although there was also the possibility of direct transmission from patient to patient. Nine patients acquired the unique strain of MRSA and once acquired it proved difficult to eradicate, although in the majority, the infection did not appear to be clinically significant. However, in two patients MRSA contributed to a fatal outcome: these were the two most elderly patients and were the only two who were receiving systemic corticosteroids. The outbreak was brought under control with rigorous hygienic measures and the decision to discharge all patients with MRSA from the day-care unit. Repeat screening (swabs of nose, axilla and groin) of all day-care unit and in-patients 11 months after the last MRSA case showed no evidence of any residual MRSA infection in the day-care unit.

Typing of consecutive methicillin-resistant Staphylococcus aureus isolates from intensive care unit patients and staff with pulsed-field gel electrophoresis

Six consecutive methicillin-resistant Staphylococcus aureus (MRSA) isolates obtained in a 2-month period from tracheal aspirates of six intensive care unit (ICU) patients with nosocomial pneumonia and two MRSA isolates from nasal carriers among staff were typed to determine whether one or more strains were involved and whether nasal carriage was the source of the outbreak. Pulsed-field gel electrophoresis (PFGE) of chromosomal DNA was used to type MRSA isolates. The typing showed that the outbreak was caused by a single epidemic MRSA clone. The MRSA strain isolated from the staff was unrelated to the outbreak strain and was therefore not the source of the outbreak in this study. The source was apparently the index patient followed by transfer of MRSA to other patients on medical equipment or on the hands of staff who did not adhere strictly to infection control measures.

Methicillin-resistant Staphylococcus aureus infection in palliative care

Our objective was to assess the impact of methicillin-resistant Staphylococcus aureus (MRSA) infection in palliative care. The study was conducted at three hospices in south London, totalling 118 beds, and the following two methods were used. Firstly, a retrospective review of the notes of patients who were known to be MRSA positive at admission or were subsequently found to be MRSA positive was taken. Secondly, a prospective study of factors influencing bed occupancy in one hospice was conducted. The proportion of admissions who were MRSA positive ranged from 4% to 8% in the three hospices. Seven of the 43 patients who had MRSA suffered clinically significant infections. Risk factors for colonization and bacteraemia were similar to the general population. Sites of infection were variable and multiple and treatment regimes for eradication were variable, with varying outcomes. MRSA infection appeared to delay admission because of the need for single rooms, of which there are few Time spent cleaning rooms after discharge or death also reduced the number of available beds. It was concluded that MRSA infection is associated with significant morbidity in a small number of palliative care patients. Beds unavailable because of MRSA should be considered in bed occupancy figures, otherwise bed occupancy may appear artificially low. The psychological and financial impact of the infection in palliative care patients needs further evaluation.

Methicillin-resistant Staphylococcus aureus: a questionnaire and microbiological survey of nursing and residential homes in Barking, Havering and Brentwood

The study determined the policies and procedures for the control and prevention of methicillin-resistant Staphylococcus aureus (MRSA) and its prevalence among nursing and residential homes, and evaluated whether certain home characteristics such as bed size, staffing level, and type of home are related to the prevalence of MRSA. A 21-questionnaire survey, with primarily categorical responses, was mailed to the home managers of all the 121 nursing and residential homes in the district, following which a simple, stratified random sample of 28 (23.14%) homes was taken and all agreeing residents screened from multiple sites for MRSA. Seventy-seven (63.6%) homes returned a completed questionnaire, 13 (46.4%) of whom agreed to participate in the microbiological study. The response rates for returning questionnaires and agreeing to participate in the microbiological study were similar for nursing and residential homes (65% vs. 60%; 67% vs. 40%; P = 0.12; P = 0.62), respectively. Nursing homes had a mean bed size of 30 (95% Confidence Interval (CI) 17-43), not significantly different from residential homes of 23 (95% CI 18-27; P = 0.26). The nursing homes employed a mean of 8.6 (95% CI 4.7-12.5) staff nurses per home; significantly higher than residential homes with a mean of 1.6 (95% CI 0.3-2.8; P = 0.006). No significant differences in mean number of home care assistants employed per home (22.8; 95% CI 12.4-33.13; and 14.4; 95% CI 11.83-16.90; P = 0.098, for nursing and residential homes, respectively) were observed. None of the homes had employed infection control practitioners. Only four (6.8%) of the responding homes stated that MRSA was a problem. Nursing homes were not significantly more likely to have admission policies for colonized person than residential homes (10/13 vs. 40/55, P = 1.00). Of the fifty-five (71.4%) homes who had admission policies, 40 (72.7%) stated that persons colonized/infected with MRSA would not be accepted, while 12 (21.8%) would accept such persons in single-room isolation and/or barrier nursing. Greater proportions of residential homes than nursing homes would not accept admission of persons with documented MRSA colonization (30/35 vs. 4/10, P = 0.007). Four (9.1%) homes (three nursing) had identified a total of five residents colonized/infected with MRSA in 5 years prior to the survey. Two hundred and forty-six residents were screened (552 sites), two (0.81%) of whom were found to be colonized in the nose (one resident) and in the groin (two residents) with MRSA, giving a 2-month weighted point prevalence rate of 0.14% (95% CI 0.01-0.26%). We conclude that in our district the nursing staffing levels and control measures vary widely within these homes, while the prevalence of residents who are colonized/infected with MRSA is lower than in other areas. We suggest that the exclusion admission policy for MRSA positive patients should be abandoned and targeted infection control programmes be instituted.

Clonal heterogeneity, distribution, and pathogenicity of methicillin-resistant Staphylococcus aureus

Four thousand eighty-eight Staphylococcus aureus isolates obtained from patients hospitalised in a university clinic and four community hospitals over a period of one year were screened for methicillin resistance. A resistance rate of 5% was detected among initial isolates. Distribution of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus showed an increased prevalence of MRSA in clinically significant specimens such as blood, central venous catheter tips, bronchial secretions, and wound secretions. Typing of 110 MRSA strains (initial isolates) by macrorestriction analysis of chromosomal DNA revealed 26 different genotypes that could be divided into five epidemic and 21 sporadic strains. More than 50% of all isolates belonged to one type that was confirmed to be closely related to the "southern-German" epidemic strain. Production of virulence factors such as enterotoxin A-D and toxic shock syndrome-toxin 1 among MRSA strains (initial isolates) occurred in ten of 26 different MRSA types. A strong correlation between genotype and toxin production was demonstrated.

Once is an Incident: MRSA and the Occupational Therapist

Occupational therapists are increasingly finding themselves working in settings where they are exposed to methicillin-resistant Staphylococcus aureus (MRSA). This article explores the epidemiological and clinical background to this area, highlighting some of the most important issues.

Methicillin-resistant Staphylococcus aureus: investigation of a hospital outbreak using a case-control study

A retrospective case-control study of 50 MRSA-positive patients was carried out during an outbreak of methicillin-resistant Staphylococcus aureus (MRSA) at an acute general hospital in London. Controls were randomly selected from MRSA-negative patients admitted during the outbreak period. Risk factors investigated included length of admission prior to screening, number of ward changes, main diagnosis, extent of staff contact, pressure sores, surgical and other invasive procedures and antibiotic treatment. Outcome variables examined were rates of infection (versus colonization) with MRSA and mortality. Patients with MRSA were in hospital longer before microbiological specimens were taken and moved wards more often than controls. In a logistic regression analysis, length of stay in hospital, pressure sores, physiotherapy and surgical procedures were associated with a significantly increased risk of acquiring MRSA. Odds ratios (and 95% confidence intervals) for having acquired MRSA were: 8.3 (1.02-71.43) if a patient had pressure sores; 3.7 (1.10-12.5) if they received physiotherapy; and 3.2 (1.82-10.0) if they underwent surgical procedures. The rate of clinical infection amongst patients with this strain of MRSA was 26% and included life-threatening infections such as septicaemia, underlining the potential virulence of MRSA. Surgery and physiotherapy may have been markers of debility. Physiotherapy was probably a marker of increased rates of contact with all hospital staff, and high standards of hand hygiene should be promoted amongst all staff as the most important factor in controlling an outbreak of MRSA. Good bed management is essential for hospital infection control.

Methicillin-resistant Staphylococcus aureus in wound care

A discussion detailing the development of antibiotic-resistant strains of Staphylococcus aureus and offering guidelines for infection control procedures.

Teicoplanin. A pharmacoeconomic evaluation of its use in the treatment of gram-positive infections

Teicoplanin, a glycopeptide antibiotic, is active against Gram-positive organisms, including methicillin-resistant staphylococci. It has demonstrated similar efficacy to vancomycin in the treatment of Gram-positive infections in febrile patients with neutropenia; fewer comparative data are available in patients with other infection types. Compared with vancomycin, teicoplanin is associated with less nephrotoxicity, appears to cause fewer anaphylactoid reactions, requires less monitoring and is more convenient to administer (once daily by intravenous bolus or intramuscular injection vs 2 to 4 times daily by intravenous infusion). Two European cost-minimisation studies have demonstrated that while the acquisition cost per dose of teicoplanin was approximately twice that of vancomycin, the cost of 2 weeks' therapy with either agent was similar (difference of 1 to 2%). However, in order to fully explore potential differences between these agents, a full economic analysis which considers all treatment-related costs is needed. Home therapy of Gram-positive infections, a setting in which teicoplanin may be preferred over vancomycin because of its tolerability profile and ease of administration, is particularly worthy of future economic study. Thus, there are a number of areas needing further study before the optimum formulary positioning of teicoplanin can be definitely stated. Nevertheless, present evidence suggests that teicoplanin is likely to have pharmacoeconomic advantages over vancomycin in at least some situations.

A major outbreak of methicillin-resistant Staphylococcus aureus caused by a new phage-type (EMRSA-16)

An outbreak of methicillin-resistant Staphylococcus aureus (MRSA) infection caused by a novel phage-type (now designated EMRSA-16) occurred in three hospitals in East Northamptonshire over a 21-month period (April 1991--December 1992). Four hundred patients were colonized or infected. Seven patients died as a direct result of infection. Chest infections were significantly associated with the outbreak strain when compared with methicillin-sensitive S. aureus. Twenty-seven staff and two relatives who cared for patients were also colonized. A 'search and destroy' strategy, as advocated in the current UK guidelines for control of epidemic MRSA was implemented after detection of the first case. Despite extensive screening of staff and patients and isolation of colonized and infected patients, the outbreak strain spread to all wards of the three hospitals except paediatrics and maternity. A high incidence of throat colonization (51%) was observed. Failure to recognize the importance of this until late in the outbreak contributed to the delay in containing its spread. Key parts of the strategy which eventually contained the local outbreak were the establishment of isolation wards in two hospitals, treatment of all colonized patients and staff to eradicate carriage and screening of all patients upon discharge from wards where MRSA had ever been detected. EMRSA-16 spread to neighbouring hospitals by early 1992 and to London and the South of England by 1993. It is distinguished from other epidemic strains by its characteristic phage-type, antibiogram (susceptibility to tetracycline and resistance to ciprofloxacin), and in the pattern given on pulse field electrophoresis.