Impact of methicillin resistance in S. aureus

The prevalence of methicillin resistance among Staphylococcus aureus strains and the incidence of clinical infections due to methicillin-resistant S. aureus (MRSA) are disturbingly high in France. Evaluations of the negative impact of methicillin-resistance in S. aureus are needed to establish priorities for infection control programs. Whether methicillin resistance independently affects the frequency of S. aureus infections remains unclear. It follows that the impact of methicillin resistance in terms of morbidity, mortality, economic costs, and ecology should be assessed using both infection-free patients and patients infected with susceptible strains as controls. There is abundant direct and indirect evidence that morbidity related to MRSA is at least as high as that related to methicillin-susceptible S. aureus (MSSA). Whether MRSA strains are more virulent than MSSA strains is controversial. Serious MRSA infections are associated with significant mortality and account for a very large part of the overall infection-related mortality rate. Opinion remains divided as to whether multiple-drug resistant S. aureus strains are associated with higher mortality rates than other S. aureus strains. The economic cost of MRSA infections is huge and considerably higher than that of MSSA infections. The heavy glycopeptide use related to the high prevalence of MRSA infections has generated problems in the management of patients with enterococcal infections and may in the near future result in a pandemic of glycopeptide-resistant MRSA infections. The development of programs designed to control the clonal dissemination of MRSA strains is a top priority from both a medical and an economic viewpoint.     

Typing of Methicillin resistant Staphylococcus aureus: a technical review

Increasing prevalence of Methicillin-resistant Staphylococcus aureus (MRSA) worldwide is a growing public health concern. MRSA typing is an essential component of an effective surveillance system to describe epidemiological trends and infection control strategies. Current challenges for MRSA typing are focused on selecting the most appropriate technique in terms of efficiency, reliability, ease of performance and cost involved. This review summarises the available information on application, potential and problems of various typing techniques in discriminating the strains and understanding the epidemiology of MRSA strains. The phenotypic methods in general are easier to perform, easier to interpret, cost effective and are widely available, however less discriminatory. The genotypic methods are expensive and technically demanding, however more discriminatory. Newer technologies involving sequencing of various genes are coming up as broadly applicable and high throughput typing systems. Still there is no consensus regarding the single best method for typing of MRSA strains. Phage typing is recommended as first line approach in epidemiological investigation of MRSA strains. PFGE remains the gold standard for characterisation of outbreak strains. DNA sequencing methods including MLST, spa typing, SCCmec typing and toxin gene profile typing are more practical methods for detecting evolutionary changes and transmission events. The choice of typing technique further depends on the purpose of the study, the facilities available and the utility of data generated to answer a desirable research question. A need for harmonisation of typing techniques by following standard protocols is emphasised to establish surveillance networks and facilitate global MRSA control.     

Frequency and possible infection control implications of gastrointestinal colonization with methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of health care-associated infections. Multiple factors, including transmission from unrecognized reservoirs of MRSA, are responsible for failure to control the spread of MRSA. We conducted prospective surveillance to determine the frequency of gastrointestinal colonization with MRSA among patients and its possible impact on nosocomial transmission of MRSA. Stool specimens submitted for Clostridium difficile toxin A/B assays were routinely inoculated on colistin-naladixic acid agar plates, and S. aureus was identified by using standard methods. Methicillin resistance was confirmed by growth on oxacillin-salt screening agar. For patients whose stool yielded MRSA, information regarding any previous cultures positive for MRSA or other organisms that would require contact precautions was obtained from the laboratory's computer system. During a 1-year period, 151 (9.8%) of 1,543 patients who had one or more stool specimens screened had MRSA in their stool. Ninety-three (62%) of the 151 patients had no previous history of MRSA colonization or infection. Of these 93, 75 were inpatients. Sixty (80%) of the 75 inpatients with no previous history of MRSA were not under "contact precautions." The 60 patients would have spent an estimated total of 267 days without being placed under contact precautions if their positive stool cultures had not resulted in their being isolated. Placing patients under contact precautions based on their positive stool cultures prevented an estimated 35 episodes of MRSA transmission. We conclude that gastrointestinal colonization with MRSA may serve as an unrecognized reservoir from which transmission of MRSA may occur in health care facilities.     

Can we do better in controlling and preventing methicillin-resistant Staphylococcus aureus (MRSA) in the intensive care unit (ICU)?

Methicillin-resistant Staphylococcus aureus (MRSA) is prevalent in many hospitals, but many of its most serious clinical manifestations, such as bloodstream infection and ventilator-associated pneumonia, are seen in the intensive care unit (ICU). Many interventions to prevent and control MRSA were initially pioneered in the ICU and subsequently extended to the rest of the hospital. Recent studies confirm how many of these are effective. Active surveillance reveals higher numbers of cases when compared with the sole use of clinical specimens to identify MRSA-positive patients. Although one recent study from the UK has suggested that isolation has no impact on MRSA transmission in the ICU, current recommendations include isolation or cohorting, combined with decolonisation (e.g., mupirocin to the nose and chlorhexidine baths) as major control measures. However, the excessive use of mupirocin for nasal MRSA decolonisation leads to resistance. Improved compliance with hand hygiene recommendations and better antibiotic stewardship are also important. Rapid diagnosis such as PCR may utilise isolation facilities more effectively by identifying MRSA patients earlier. However, all these measures must be combined with adequate numbers of staff and suitable space and facilities, e.g., single rooms, to be maximally effective. Finally, while much can be done within the ICU itself, MRSA in the ICU often reflects the difficulties elsewhere in the acute hospital and the health service generally, in terms of the control and prevention of healthcare-associated infection.     

Characterization of PVL‐positive MRSA from Norway

Norway is a country in which the Methicillin‐resistant Staphylococcus aureus (MRSA) prevalence has been low for the last decades. There are virtually no epidemic, hospital‐acquired MRSA because of an emphasis on strict infection control rules and restrictive use of antibiotics. However, community‐acquired and/or Panton‐Valentine leucocidin (PVL)‐positive MRSA need to be monitored as these strains are transmitted outside of healthcare facilities and cannot be contained by healthcare‐centred strategies. All 179 non‐repetitive isolates of PVL‐positive MRSA that were received during 2011 at the regional infection control laboratory at Akershus University Hospital were preserved and spa typed. Seventy isolates were further characterized by DNA microarray hybridization. The most common PVL‐MRSA lineages were ST8‐MRSA‐IV and CC30‐MRSA‐IV. Further common clones were CC80‐MRSA‐IV and CC5‐MRSA‐IV. Other clones were found sporadically. These included ST772‐MRSA‐V and ST834‐MRSA‐IV, the latter in patients with epidemiological connections to the Philippines. Small‐scale family outbreaks affecting at least 49 individuals were noted, with numbers of known cases per outbreak ranging from two to seven. At least 24 cases were related to foreign travel to Eritrea, India, Iraq, Macedonia, Pakistan, the Philippines, Poland, Singapore, Turkey, the USA and Vietnam. These data show that community‐acquired/PVL‐positive MRSA are not yet a major public health problem in Southern Norway. Our study corroborates the current practice of mandatory screening of patients and staff with travel histories, admissions or employment in healthcare institutions outside the Scandinavian countries or with known MRSA contacts.     

Le staphylocoque doré résistant à la méticilline dans les services et établissements de moyen séjour : quelle stratégie proposer ?

BACKGROUND: The risk associated with methicillin-resistant Staphylococcus aureus (MRSA) has been decreasing for several years in intensive care departments, but is now increasing in rehabilitation and chronic-care-facilities (R-CCF). The aim of this study was to use published data and our own experience to discuss the roles of screening for MRSA carriers, the type of isolation to be implemented and the efficiency of chemical decontamination. DISCUSSION: Screening identifies over 90% of patients colonized with MRSA upon admission to R-CCF versus only 50% for intensive care units. Only totally dependent patients acquire MRSA. Thus, strict geographical isolation, as opposed to "social reinsertion", is clearly of no value. However, this should not lead to the abandoning of isolation, which remains essential during the administration of care. The use of chemicals to decolonize the nose and healthy skin appeared to be of some value and the application of this procedure could make technical isolation unnecessary in a non-negligible proportion of cases. SUMMARY: Given the increase in morbidity associated with MRSA observed in numerous hospitals, the emergence of a community-acquired disease associated with these strains and the evolution of glycopeptide-resistant strains, the voluntary application of a strategy combining screening, technical isolation and chemical decolonization in R-CCF appears to be an urgent matter of priority.     

The impact of MRSA infection in the airways of children with cystic fibrosis; a case-control study

The prevalence of Methicillin Resistant Staphylococcus Aureus (MRSA) in patients with Cystic Fibrosis (CF) has risen dramatically over the past 10 years. The clinical significance of MRSA in CF patients remains undetermined. We conducted a review of patients with CF infected with MRSA over a 10 year period at Our Lady's Children's Hospital, Crumlin between 1999 and 2009. We collected data from 24 patients infected with MRSA and 24 control patients without MRSA There was a significant difference between the two groups in the rate of decline in percentage FEV1 two years after MRSA infection (Difference: -17.4, 95% CI: -30.48, -4.31, p = 0.01). A similar trend was seen for FVC% and FEF25-75% predicted. This study suggests that persistent MRSA infection in the airways of children with CF is associated with diminished lung function two years post acquisition, when compared to a matched control cohort without MRSA.     

Nationwide Survey Shows that Methicillin-Resistant Staphylococcus aureus Strains Heterogeneously and Intermediately Resistant to Vancomycin Are Not Disseminated throughout Japanese Hospitals

A total of 6,625 methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates obtained from 278 hospitals throughout Japan were obtained between November and December 1997 and were examined for their sensitivities to vancomycin using Mueller Hinton (MH), brain heart infusion (BHI), agar plates, or the broth microdilution method. A concentrated inoculum of an MRSA strain or the use of highly enriched medium, such as BHI medium, allows an individual cell to grow on agar plates containing a vancomycin concentration greater than the MIC for the parent strain. However, cells of the colonies which grew on BHI agar plates containing the higher vancomycin concentrations did not acquire a level of vancomycin resistance greater than that of the parent strain and were not subpopulations of heterogeneously vancomycin-resistant MRSA. There was no significance in the fact that these colonies grew on the higher concentration of vancomycin: none showed stable resistance to vancomycin at a concentration above the MIC for the parent strain, and no cell from these colonies showed a relationship between the MIC and the ability of these colonies to grow on higher concentrations of vancomycin. The vancomycin MIC was not above 2 microg/ml for any of the cells originating from these colonies. No Mu3-type heterogeneously resistant MRSA strains, which constitutively produce subpopulations from MRSA clinical isolates with intermediate vancomycin resistance at a high frequency, were detected. There was a unipolar distribution of the MICs ranging from 0.25 to 2 microg of vancomycin/ml among the 6,625 MRSA clinical isolates, indicating that there was no Mu50-type intermediately vancomycin-resistant MRSA (MIC, 8 microg/ml by National Committee for Clinical Laboratory Standards criteria) among the clinical isolates, and there was no evidence of dissemination of Mu3-type MRSA heteroresistant to vancomycin.     

A Rapid and High-Throughput Screening Approach for Methicillin-Resistant Staphylococcus aureus Based on the Combination of Two Different Real-Time PCR Assays

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen that has been responsible for major nosocomial epidemics worldwide. For infection control programs, rapid and adequate detection of MRSA is of great importance. We developed a rapid and high-throughput molecular screening approach that consists of an overnight selective broth enrichment, followed by mecA, mecC, and S. aureus-specific (SA442 gene) real-time PCR assays, with subsequent confirmation using a staphylococcal cassette chromosome mec element (SCCmec)-orfX-based real-time PCR assay (GeneOhm MRSA assay) and culture. Here, the results of the screening approach over a 2-year period are presented. During this period, a total of 13,387 samples were analyzed for the presence of MRSA, 2.6% of which were reported as MRSA positive. No MRSA isolates carrying the mecC gene were detected during this study. Based on the results of the real-time PCR assays only, 95.2% of the samples could be reported as negative within 24 h. Furthermore, the performance of these real-time PCR assays was evaluated using a set of 104 assorted MRSA isolates, which demonstrated high sensitivity for both the combination of mecA and mecC with SA442 and the BD GeneOhm MRSA assay (98.1% and 97.1%, respectively). This molecular screening approach proved to be an accurate method for obtaining reliable negative results within 24 h after arrival at the laboratory and contributes to improvement of infection control programs, especially in areas with a low MRSA prevalence.     

Laboratory tools and strategies for methicillin-resistant Staphylococcus aureus screening, surveillance and typing: state of the art and unmet needs

The public health burden caused by methicillin-resistant Staphylococcus aureus (MRSA) infections is now widely recognized, and is a cause of public alarm. Effective MRSA risk management in the healthcare system as well as in the community should rely on accurate detection of reservoirs and sources of transmission, as well as on close monitoring of the impact of interventions on disease incidence and bacterial dissemination. MRSA carrier screening and disease surveillance, coupled with molecular typing, are key information tools for integrated MRSA control and individual risk assessment. These tools should be tailored to the distinct needs of local interventions and national prevention programmes. Surveillance schemes should primarily inform local staff and serve as quality assurance about MRSA risk management. New technologies, including the use of selective culture media and real-time PCR assays, allow faster detection of MRSA carriers upon admission or during stay in healthcare institutions. More research is needed to ascertain their cost-effectiveness for MRSA control. Likewise, tremendous progress has been made concerning molecular typing methods, with optimization and standardization of sequence-based technologies offering broad applicability and high throughput. However, no single S. aureus typing method is yet providing fully reliable information within the range of discrimination needed for public health action. Further refinement of genotyping methods and international harmonization of surveillance and typing schemes must be achieved to facilitate global MRSA control.     

Nosocomial infections and clinical microbiology

Hospital-acquired infection with strains of methicillin-resistant Staphylococcus aureus (MRSA) have considerably increased in recent years. In addition to being resistant to methicillin, these strains are resistant to practically all forms beta-lactams, aminoglycosides and many other antibiotics. There appears no cost-effective control and preventive measures for this common but also potentially life-threatening disease. Although not clearly presented, the overall cost for the treatment of patients infected with MRSA should be enormous. Can laboratory medicine (or clinical microbiology) contribute to this global medical problem? Multiple strains of MRSA circulate within a hospital and some strains are even localized within specific wards. These facts suggest yet undisclosed routes of transmission and/or foci of infection. Triumph over these versatile organisms may have to await the development of new antibiotics effective for MRSA.     

Body site colonization in patients with community-associated methicillin-resistant Staphylococcus aureus and other types of S. aureus skin infections

Efforts to control spread of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) are often based on eradication of colonization. However, the role of nasal and non-nasal colonization in the pathogenesis of these infections remains poorly understood. Patients with acute S. aureus skin and soft tissue infection (SSTI) were prospectively enrolled. Each subject's nasal, axillary, inguinal and rectal areas were swabbed for S. aureus and epidemiological risk factors were surveyed. Among the 117 patients enrolled, there were 99 patients who had an SSTI and for whom data could be analysed. Sixty-five patients had a CA-MRSA SSTI. Among these patients, MRSA colonization in the nares, axilla, inguinal area and rectum was 25, 6, 11 and 13%, respectively, and 37% overall were MRSA colonized. Most (96%) MRSA colonization was detected using nose and inguinal screening alone. Non-nasal colonization was 25% among CA-MRSA patients, but only 6% among patients with CA-methicillin-susceptible S. aureus (MSSA) or healthcare-associated MRSA or MSSA. These findings suggest that colonization patterns in CA-MRSA infection are distinct from those in non-CA-MRSA S. aureus infections. The relatively high prevalence of non-nasal colonization may play a key role in CA-MRSA transmission and acquisition of infection.     

Role of a clinical laboratory center as a correlational center for infection control

The prevention of hospital acquired infection is one of the most critical managements for the maintenance of high clinical quality. Surveillance such as the isolation rate of MRSA (methicillin resistant Staphylococcus aureus), MDRP (multidrug-resistant Pseudomonas aeruginosa) and catheter associated blood stream infection rate are useful tools for infection control. In these surveillances, the clinical laboratory center plays an important role in hospitals. Recent studies have shown that community-acquired MRSA has spread rapidly in the United States and clonal MDRP has also spread in Japan. In our studies, similar genotyped MDRP was isolated from several hospitals in the same region. These results suggested that infection control associated with regional hospitals is important to prevent the spread of antimicrobial resistant pathogens. The clinical laboratory center should also play an important role in regional infection control.     

Costs of healthcare-associated methicillin-resistant Staphylococcus aureus and its control

Methicillin-resistant Staphylococcus aureus (MRSA) clones have caused a huge worldwide epidemic of hospital-acquired infections over the past 20–30 years and continue to evolve, including the advent of virulent community strains. The burden on healthcare services is highly significant, in particular because MRSA has not replaced susceptible staphylococcal infection but is an additional problem. Treatment strategies for MRSA are suboptimal and compromise the care of patients. MRSA is associated with serious morbidity and mortality, both within and without hospitals. Although the literature on the costs of MRSA and its control is suboptimal, it is clear that the control of MRSA is highly desirable and likely to be cost-effective. Any compromises in control are likely to be false economies.     

What Is the Origin of Livestock-Associated Methicillin-Resistant Staphylococcus aureus Clonal Complex 398 Isolates from Humans without Livestock Contact? An Epidemiological and Genetic Analysis

Fifteen percent of all methicillin-resistant Staphylococcus aureus (MRSA) clonal complex 398 (CC398) human carriers detected in The Netherlands had not been in direct contact with pigs or veal calves. To ensure low MRSA prevalence, it is important to investigate the likely origin of this MRSA of unknown origin (MUO). Recently, it was shown that CC398 strains originating from humans and animals differ in the presence of specific mobile genetic elements (MGEs). We hypothesized that determining these specific MGEs in MUO isolates and comparing them with a set of CC398 isolates of various known origin might provide clues to their origin. MUO CC398 isolates were compared to MRSA CC398 isolates obtained from humans with known risk factors, a MRSA CC398 outbreak isolate, livestock associated (LA) MRSA CC398 isolates from pigs, horses, chickens, and veal calves, and five methicillin-susceptible Staphylococcus aureus (MSSA) CC398 isolates of known human origin. All strains were spa typed, and the presence or absence of, scn, chp, φ3 int, φ6 int, φ7 int, rep7, rep27, and cadDX was determined by PCRs. The MRSA CC398 in humans, MUO, or MRSA of known origin (MKO) resembled MRSA CC398 as found in pigs and not MSSA CC398 as found in humans. The distinct human MSSA CC398 spa type, t571, was not present among our MRSA CC398 strains; MRSA CC398 was tetracycline resistant and carried no φ3 bacteriophage with scn and chp. We showed by simple PCR means that human MUO CC398 carriers carried MRSA from livestock origin, suggestive of indirect transmission. Although the exact transmission route remains unknown, direct human-to-human transmission remains a possibility as well.     

Evaluation of the efficacy of a multiresistant bacteria control programme in a teaching hospital,studying the evolution of methicillin-resistant Staphylococcus aureus incidence

Methicillin-resistant Staphylococcus aureus (MRSA) constitute the most important multiresistant bacteria (MRB) recovered in French hospitals. Our objective was to measure these MRSA diffusion in our hospital to evaluate the MRB control programme which had been implemented in the beginning of 1999. This study was conducted in a teaching hospital containing 1800 beds, from February 1999 to January 2001. All MRSA isolated in clinical samples were included. Duplicates (same bacteria in the same patient) were excluded. The detection of methicillin-resistance was performed at 30 degrees C, by disk diffusion method. Incidence densities were determined with their 95% confidence interval (CI 95%). Their evolution by four-month period was evaluated with the chi-square test for trend. During the two-year period, 866 MRSA were isolated. The global incidence was 0,88 per 1000 patient-days (PD) (IC 95% = left open bracket 0,83-0,93 right open bracket ). For cases acquired in our hospital the incidence was 0,66 per 1000 PD, whereas it was 0,26 per 1000 PD for imported cases. Concerning the evolution of incidences, no significant trend was observed for global incidence. The incidence of acquired MRSA decreased during the first year, but increased thereafter. The incidence of imported MRSA increased with a significant trend (p < 10(-5)). The number of these imported MRSA isolated in our hospital was twice fold higher in 2000. This study emphasizes an important actual problem : the increase of patient colonization pressure at the time of admission in hospitals. This increase, which can be due in part to a community transmission, is responsible for a reduction of the efficacy of MRSA control programmes.     

Changing molecular epidemiology of methicillin-resistant Staphylococcus aureus in a small geographic area over an eight-year period

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) at an international level shows that most MRSA strains belong to a few pandemic clones. At the local level, a predominance of one or two clones was generally reported. However, the situation is evolving and new clones are emerging worldwide, some of them with specific biological characteristics, such as the presence of Panton-Valentine leucocidin (PVL). Understanding these changes at the local and international levels is of great importance. Our objective was to analyze the evolution of MRSA epidemiology at multiple sites on a local level (Western Switzerland) over a period of 8 years. Data were based on MRSA reports from seven sentinel laboratories and infection control programs covering different areas. Pulsed-field gel electrophoresis was used to type MRSA isolates. From 1997 to 2004, a total of 2,256 patients with MRSA were reported. Results showed the presence of four predominant clones (accounting for 86% of patients), which could be related to known international clones (Berlin, New York/Japan, Southern Germany, and Iberian clones). Within the small geographic region, the 8-year follow-up period in the different areas showed spacio-temporal differences in the relative proportions of the four clones. Other international MRSA clones, as well as clones showing genetic characteristics identical to those of community-acquired MRSA (SCCmec type IV and the presence of PVL genes), were also identified but presumably did not disseminate. Despite the worldwide predominance of a few MRSA clones, our data showed that at a local level, the epidemiology of MRSA might be different from one hospital to another. Moreover, MRSA clones were replaced by other emerging clones, suggesting a rapid change.     

Heterogeneity of disease and clones of community-onset methicillin-resistant Staphylococcus aureus in children attending a paediatric hospital in Belgium

The increase in the number of methicillin-resistant Staphylococcus aureus (MRSA) infections in children has prompted paediatricians to broaden th empirical treatment of common community-onset (CO) infections in children in several countries. Most European countries have reported low rates of CO-MRSA infection, but limited data on paediatric CO-MRSA infections are available. A prospective study was conducted from January 2002 to December 2004 in Brussels. CO-MRSA was defined as MRSA first detected by culture within 48 h of admission or in outpatients. Clinical and epidemiological data were recorded. CO-MRSA strains were genotyped by pulsed-field gel electrophoresis and multilocus sequence typing. Staphylococcal chromosomal cassette mec, toxin (Panton-Valentin leukocidin (PVL), toxic shock syndrome toxin 1, and Eta/b), enterotoxin and antibiotic resistance genes were detected by PCR. The antibiotic resistance phenotype was determined by disk diffusion. S. aureus was isolated in 1681 children. Among these, 107 harboured MRSA. Fifty-one children were colonized or infected by CO-MRSA, 20% of whom had no healthcare exposure. Twelve infants <3 months old and five cystic fibrosis patients were colonized. None of the 22 infected patients (59% with acute otitis media and 36% with skin and soft tissue infections (SSTIs)) required hospitalization. Two-thirds of them failed to respond to empirical antibiotic therapy. The 37 characterized CO-MRSA strains were genetically diverse. Most of them had healthcare-associated genotypes. Only six strains were PVL-positive, all of which were ciprofloxacin-susceptible and more common in children with SSTIs (p 0.001). CO-MRSA remains uncommon in our paediatric population. So far, there is no need to modify the empirical treatment of common S. aureus infections. Monitoring of MRSA rates in S. aureus CO infections remains mandatory, and further investigation is warranted to establish the source of colonization in young infants.     

Detection of meticillin-resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> and Panton-Valentine leukocidin directly from clinical samples and the development of a multiplex assay using real-time polymerase chain reaction

Meticillin-resistant Staphylococcus aureus (MRSA) is a major pathogen responsible for significant numbers of healthcare-associated infections and isolates containing Panton-Valentine leukocidin (PVL) that cause severe skin infections are emerging as a serious problem. The rapid detection of MRSA would be an invaluable tool in a diagnostic laboratory. The aim of this study is to develop real-time polymerase chain reaction (PCR) assays for the detection of MRSA and PVL directly from clinical samples, and then combining these assays. Individual assays for MRSA (SCCmec) and PVL (lukF and lukS) were optimised and evaluated with screening and wound swabs, respectively. MRSA- and PVL-positive isolates were detected by the assays with an analytical sensitivity of 100 cfu per reaction. No other bacterial species were amplified. Fifty of 402 (12.4%) nasal swabs were positive by culture and PCR. Four of the 402 (1.0%) swabs were PCR-positive/culture-negative. Three of the 402 (0.7%) swabs were PCR-negative/culture-positive. The sensitivity of the MRSA assay is 95% and the specificity is 99% using conventional culture as the gold standard. Five of 240 wound swabs (2.1%) were positive for PVL. Three of the PVL-positive swabs were meticillin-sensitive Staphylococcus aureus (MSSA) and two were MRSA. The MRSA assay is a powerful and sensitive diagnostic tool, giving rapid results and could allow more timely treatment and infection control decisions to be taken. It can also, when combined with the PVL assay, provide valuable epidemiological information.     

Methicillin-resistant Staphylococcus aureus (MRSA) infection--significance of MRSA in respiratory tract infection

We have examined background factors in MRSA infection in cases in which S. aureus had been isolated from sputa. The incidence of isolation of S. aureus was high and still increasing in expectorated sputa, and causative organisms in the cases of pneumonia and autopsied lungs. A significant correlation was observed between high incidence of isolation of S. aureus and abuse of third-generation cephems. MRSA isolation rates of inpatients was higher than that of outpatients. Among the inpatients such cases with severe underlying diseases and prolonged admission showed the highest incidence of isolation of MRSA. There seemed to be a correlation between distribution of patients with S. aureus and that of rooms with S. aureus in the air. This suggests nosocomial infection. Although MRSA was frequently isolated from sputa, most cases showed no signs of infection, and this suggested that they had been transient colonization. Such antimicrobial agents as rifampicin, teicoplanin, vancomycin reveal excellent antibacterial activity against MRSA and minocycline, ofloxacin were moderately effective. The physician must be informed of the significance of MRSA, because their understanding of MRSA still remains insufficient.