Methicillin-resistant Staphylococcus aureus and Acinetobacter baumannii: An unexpected difference in epidemiologic behavior

Background: The Dutch guideline on hospital policy for the prevention of nosocomial spread of methicillin-resistant Staphylococcus aureus (MRSA) states that patients transferred from hospitals abroad must be placed in strict isolation immediately on admission to a hospital in the Netherlands. Three patients colonized with both MRSA and a multiresistant Acinetobacter were transferred from hospitals in Mediterranean countries to 3 different hospitals in the Netherlands. Despite isolation precautions, Acinetobacter spread in 2 of the 3 hospitals, whereas nosocomial spread of MRSA did not occur. Methods: For outbreak analysis, the Acinetobacter isolates, identified as Acinetobacter baumannii by the use of amplified ribosomal DNA restriction analysis, were comparatively typed by 4 methods. Comparison of isolation measures in the hospitals was performed retrospectively. Results: In the 2 hospitals in which nosocomial spread of Acinetobacter occurred, most of the epidemiologically related isolates were indistinguishable from the index strains. In these 2 hospitals, isolation measures were in concordance with those recommended for the prevention of contact transmission. The precautions of the hospital in which no outbreak occurred included the prevention of airborne transmission. Conclusions: Precautions recommended for multiresistant gram-negative organisms are insufficient for the prevention of nosocomial spread of multiresistant Acinetobacter . The airborne mode of spread of acinetobacters should be taken into account, and guidelines should be revised accordingly. (AJIC Am J Infect Control 1998;26:544-51)     

Control of naeethicillin-resistant Staphylococcus aureus in a pediatric burn unit

Background: Control of methicillin-resistant Staphylococcus aureus (MRSA) is particularly difficult in burn units, which are often cited as sources of hospital-wide MRSA outbreaks. We developed a successful MRSA control program and document here its apparent effectiveness in controlling MRSA transmission in a pediatric burn unit.Methods: An MRSA control program that included surveillance culturing, clinician feedback, flexible, site-specific isolation, and a list of known carriers was consistently applied in a pediatric burn unit through a 7-year period. Microbiology reports of MRSA isolates from patients and environmental surfaces and records of all patients from whom MRSA was isolated were reviewed.Results: During calendar years 1985 through 1991, a total of 991 acutely burned children were admitted to the Boston unit of the Shriners Burns Institute. Forty MRSA cases (4%) were identified. One patient both had MRSA at admission and met our criteria for nosocomial MRSA. Of the remaining 39 patients, 11 had MRSA at admission and 28 had nosocomial MRSA. There were 17 wound infections, two cases of pneumonia, and two bloodstream infections. No deaths were attributed to MRSA sepsis.Conclusion: An MRSA control program including surveillance culturing, clinician feedback, flexible, site-specific isolation, and a list of known carriers is associated with a low rate of nosocomial MRSA in a pediatric burn unit.     

Methicillin-resistant Staphylococcus aureus (MRSA) in Europe: which infection control measures are taken?

Background

The prevalence of hospital-acquired Methicillin-resistant Staphylococcus aureus (MRSA) infections shows a huge variety across Europe. Some countries reported a reduction in MRSA frequency, while in others countries increasing MRSA rates have been observed. To reduce the spread of MRSA in the healthcare setting, a sufficient MRSA management is essential. In order to reflect the MRSA management across Europe, MRSA prevention policies were surveyed in ten countries.

Materials and methods

The survey was performed by questionnaires in European intensive care units (ICUs) and surgical departments (SDs) in 2004. Questionnaires asked for availability of bedside alcohol hand-disinfection, isolation precautions, decolonization and screening methods. The study was embedded in the Hospital in Europe Link for Infection Control through Surveillance (HELICS) Project, a European collaboration of national surveillance networks. HELICS was initiated in order to harmonize the national surveillance activities in the individual countries. Therefore, HELICS participants developed surveillance modules for nosocomial infections in ICUs and for surgical site infections (SSI). The coordination of this surveillance has now been transferred to the European Centre for Disease Prevention and Control (ECDC).

Results

A total of 526 ICUs and 223 SDs from ten countries sent data on organisational characteristics and policies, demonstrating wide variations in care. Substantial variation existed in availability of bedside alcohol hand-disinfection, which was much higher in participating ICUs rather than in SDs (86 vs. 59%). Surveillance cultures of contact patients were obtained in approximately three-fourths of all SDs (72%) and ICUs (75%). Countries with decreasing MRSA proportions showed especially strict implementation of various prevention measures.

Conclusion

The data obtained regarding MRSA prevention measures should stimulate infection control professionals to pursue further initiatives. Particularly, the vigorous MRSA management in countries with decreasing MRSA proportions should encourage hospitals to implement preventive measures in order to reduce the spread of MRSA.     

Methicillin-resistant Staphylococcus aureus in hospitals and the community: stealth dynamics and control catastrophes

Methicillin-resistant Staphylococcus aureus (MRSA) represents a serious threat to the health of hospitalized patients. Attempts to reduce the spread of MRSA have largely depended on hospital hygiene and patient isolation. These measures have met with mixed success: although some countries have almost eliminated MRSA or remained largely free of the organism, others have seen substantial increases despite rigorous control policies. We use a mathematical model to show how these increases can be explained by considering both hospital and community reservoirs of MRSA colonization. We show how the timing of the intervention, the level of resource provision, and chance combine to determine whether control measures succeed or fail. We find that even control measures able to repeatedly prevent sustained outbreaks in the short-term can result in long-term control failure resulting from gradual increases in the community reservoir. If resources do not scale with MRSA prevalence, isolation policies can fail "catastrophically."     

Vancomycin-resistant enterococci in intensive-care hospital settings: transmission dynamics, persistence, and the impact of infection control programs.

Vancomycin-resistant enterococci (VRE) recently have emerged as a nosocomial pathogen especially in intensive-care units (ICUs) worldwide. Transmission via the hands of health-care workers is an important determinant of spread and persistence in a VRE-endemic ICU. We describe the transmission of nosocomial pathogens by using a micro-epidemiological framework based on the transmission dynamics of vector-borne diseases. By using the concept of a basic reproductive number, R0, defined as the average number of secondary cases generated by one primary case, we show quantitatively how infection control measures such as hand washing, cohorting, and antibiotic restriction affect nosocomial cross-transmission. By using detailed molecular epidemiological surveillance and compliance monitoring, we found that the estimated basic reproductive number for VRE during a study at the Cook County Hospital, Chicago, was approximately 3-4 without infection control and 0.7 when infection control measures were included. The impact of infection control was to reduce the prevalence from a predicted 79% to an observed 36%. Hand washing and staff cohorting are the most powerful control measures although their efficacy depends on the magnitude of R0. Under the circumstances tested, endemicity of VRE was stabilized despite infection control measures, by the constant introduction of colonized patients. Multiple stochastic simulations of the model revealed excellent agreement with observed pattern. In conjunction with detailed microbiological surveillance, a mathematical framework provides a precise template to describe the colonization dynamics of VRE in ICUs and impact of infection control measures. Our analyses suggest that compliance for hand washing significantly in excess of reported levels, or the cohorting of nursing staff, are needed to prevent nosocomial transmission of VRE in endemic settings.     

Prevalence of methicillin-resistant Staphylococcus aureus in a Canadian inner-city shelter

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) colonization is increasingly of concern in community settings. However, despite a recent outbreak in Calgary, Alberta, data on the prevalence of MRSA in Canadian communities are lacking. Globally, few studies have been performed in high-risk groups such as inner-city populations. METHODS: A cross-sectional study of the prevalence of MRSA among residents and staff at three Ottawa, Ontario, shelters was conducted. All participants completed a questionnaire, and provided nasal swabs as well as one of rectal, anal or groin swabs. RESULTS: Among 84 participants, the prevalence of MRSA colonization was 2.4%. Among the resident subgroup, the prevalence was 4.5%, while no MRSA isolates were found among 40 staff participants. All isolates were USA100 (CMRSA-2) subtypes. CONCLUSIONS: The prevalence of MRSA colonization among residents is higher than baseline population rates, but is consistent with other inner-city populations. Although community outbreaks of USA300 and USA400 strains are increasingly reported, movement of nosocomial strains (ie, USA100 [CMRSA-2]) into communities remains an important avenue in the spread of MRSA and underscores the importance of nosocomial MRSA control.     

Methicillin-resistant Staphylococcus aureus: factors responsible for its incidence

INTRODUCTION: How can we explain that the proportion of methicillin-resistant Staphylococcus aureus (MRSA) varies between the European countries, ranging from < 1% in Scandinavia to > 30% in Spain, France and Italy? This paper is aimed at attempting to determine factors at the origin of the spreading of endemic MRSA strains as of the early 1980s. Those strains are characterized by their ability to develop resistance to current antibiotics and make treatment of severe and deep infections more complex. CURRENT KNOWLEDGE AND KEY POINTS: Differences in the virulence of MRSA strains and that of susceptible strains appear unlikely. MRSA prevalence seems to be a growing problem, especially in Southern Europe where rates of resistance to other anti-staphylococcal antibiotics are high. General policies for antibiotic therapy as well as the implementation of strategies for prevention and control of MRSA might be responsible for such rates. Indeed, once MRSA is introduced into a facility without control program, this multiresistant bacteria rapidly spreads within the hospital and becomes endemic, expanding its reservoir. FUTURE PROSPECTS ET PROJECTS: Due to the introduction of new methods in microbiology and communication, infection control measures including procedures for isolation and identification of MRSA reservoirs are still feasible; however, their implementation requires human and material resources. Areas requiring improvement in the detection of MRSA outbreaks are identified in this paper, with particular emphasis on the need for national surveillance of MRSA prevalence and reappraisal of MRSA control strategies in French hospitals.     

Epidemiology of Staphylococcus aureus nosocomial infections in a high-risk neonatal unit

Nosocomial infections are a significant cause of morbidity and mortality throughout the world. In developing countries it is difficult to carry out effective surveillance and control programs for this type of infection because of the cost in both human and material resources. These considerations prompted us to perform a prospective study to determine the epidemiologic and microbiologic characteristics of nosocomial infections due to Staphylococcus aureus in the High-risk Neonatal Unit (HRNU) of the Instituto Autónomo Hospital Universitario de Los Andes (IAHULA), during the period of November 1997 to October 1998. Among a total of 120 microorganisms, 24 (20%) strains of Staphylococcus aureus were isolated; 47% were recovered from blood and 33% from conjunctive samples. Among the cases of conjunctivitis, S. aureus was the only pathogen isolated in 42%. Twenty of the 24 Staphylococcus aureus strains (83%) were methicillin-resistant (MRSA). According to their resistance profiles, we established 12 groups of strains from neonates with nosocomial infections and 1 group of strains from the two carriers among the healthcare personnel detected by microbiological screening. The MeRGmR pattern was the most frequent. Plasmid analysis disclosed two profiles, each having a plasmid molecular weight over 23.130 bp. The MRSA strains isolated from the neonates and those isolated from the carriers showed the same plasmid profile. This suggests that the healthcare personnel may have acted as reservoirs of the MRSA strains found in neonates with nosocomial infection.     

Comprehensive strategy to prevent nosocomial spread of methicillin-resistant Staphylococcus aureus in a highly endemic setting

BACKGROUND: The effectiveness and feasibility of a comprehensive strategy to reduce nosocomial transmission of methicillin-resistant Staphylococcus aureus (MRSA) in a highly endemic setting have not yet been proved. Limited benefits and the high cost of such programs are the main concerns. METHODS: We prospectively evaluated the effect of an aggressive infection control program on transmission of MRSA in the University Clinic of Respiratory and Allergic Diseases. All patients with MRSA carriage during 5 years (January 1, 1998, through December 31, 2002) were included and categorized into imported or hospital-acquired cases. RESULTS: Methicillin-resistant S aureus was recovered from 223 hospitalized patients; 142 cases were imported and 81 were acquired at our institution. After introduction of the comprehensive infection control program in 1999, the annual incidence of MRSA carriage per 1000 admissions increased from 4.5 in 1998 to 8.0 in 1999 (P = .02), and remained stable thereafter. In this period, the proportion of MRSA cases acquired in our institution decreased from 50.0% in 1999 to 6.1% in 2002 (P<.001), whereas the proportion of MRSA cases transferred from other hospitals (P<.001) and nursing homes (P = .03) increased. All 19 MRSA carriers with 3 sets of follow-up cultures were successfully decolonized. CONCLUSIONS: With a comprehensive infection control program, it was possible to reduce nosocomial transmission of MRSA in a highly endemic setting. With good hand hygiene using alcohol handrub, early detection, isolation, and a decolonization strategy, containment of MRSA was achievable, despite a high rate of transferred patients with MRSA.     

Use of Rapid Diagnostic Tests in Malaria School Surveys in Kenya: Does their Under-performance Matter for Planning Malaria Control?

Malaria rapid diagnostic tests (RDTs) are known to yield false-positive results, and their use in epidemiologic surveys will overestimate infection prevalence and potentially hinder efficient targeting of interventions. To examine the consequences of using RDTs in school surveys, we compared three RDT brands used during a nationwide school survey in Kenya with expert microscopy and investigated the cost implications of using alternative diagnostic approaches in identifying localities with differing levels of infection. Overall, RDT sensitivity was 96.1% and specificity was 70.8%. In terms of classifying districts and schools according to prevalence categories, RDTs were most reliable for the < 1% and > 40% categories and least reliable in the 1–4.9% category. In low-prevalence settings, microscopy was the most expensive approach, and RDT results corrected by either microscopy or polymerase chain reaction were the cheapest. Use of polymerase chain reaction–corrected RDT results is recommended in school malaria surveys, especially in settings with low-to-moderate malaria transmission.     

Control of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of nosocomial infections worldwide. Different approaches to the control of this pathogen have met with varying degrees of success in different health care settings. Controversies exist with regards to various MRSA control strategies. The implementation and outcomes of control measures depend on several factors, including scientific, economic, administrative, governmental, and political influences. It is clear that flexibility to adapt and institute these measures in the context of local epidemiology and resources is required.     

Prevention and control of methicillin-resistant Staphylococcus aureus infections

PURPOSE OF REVIEW: This article reviews many recent publications relevant to the prevention and control of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) infection. RECENT FINDINGS: Higher risk-adjusted costs and mortality have been found for MRSA infections than for methicillin-susceptible S. aureus infections confirming their epidemiologic importance. Staphylococcal cassette chromosome mec, the genetic basis for MRSA, does not develop in methicillin-susceptible S. aureus exposed to antimicrobials. Instead virtually all patients acquire MRSA via spread. Nevertheless, antibiotic therapy provides a selective advantage for such spread, especially within healthcare settings where antimicrobial therapy is most frequent. Several studies have suggested better control of MRSA through antibiotic control, but far more studies have reported control using surveillance cultures and contact precautions for preventing spread (rather than just using standard precautions). More rapid detection of MRSA (within 6 h) has been reported using polymerase chain reaction, but studies using this method to reduce spread have not yet been published. A structured survey of research methods used regarding MRSA control noted that many studies had methodologic shortcomings (for example, none was a randomized trial), but nevertheless concluded that active detection and isolation work should be used. A Society for Healthcare Epidemiology of America guideline emphasized the same approach noting that scores of studies on multiple continents had reported success with this approach, with best results in several northern-European countries where all facilities used it routinely. SUMMARY: Improved MRSA control is possible by detecting and isolating colonized patients.     

Emergence and control of methicillin-resistant Staphylococcus aureus in a children's hospital and pediatric long-term care facility.

BACKGROUND: After a 6-year quiescence, methicillin-resistant Staphylococcus aureus (MRSA) was isolated from 30 patients in a children's hospital and a pediatric long-term care facility from November 1987 through April 1989. After six nosocomial cases had occurred at the children's hospital, increased infection control measures directed at MRSA were initiated in August 1988. Because MRSA had been identified in three patients in the pediatric long-term care facility within 24 hours of their admission to the children's hospital, other patients transferred from the pediatric long-term care facility to the children's hospital were isolated and screened for MRSA. METHODS: We reviewed the medical records of these patients and evaluated their response to therapy with rifampin alone or in combination with trimethoprim-sulfamethoxazole. RESULTS: In the 8-month period after initiation of infection control measures, MRSA was identified in 10 residents of the pediatric long-term care facility; there was also one nosocomial children's hospital case. Phage typing showed that one MRSA strain predominated in patients at the pediatric long-term care facility but did not implicate this strain as the source for MRSA introduction into the children's hospital. Of 16 patients with MRSA who completed therapy and were available for follow-up, 13 (81%) had elimination of colonization. CONCLUSION: Prompt institution of MRSA surveillance, barrier isolation, and therapy to eliminate colonization should be considered in hospitals with a new introduction of MRSA.     

Prevalence and significance of methicillin-resistant Staphylococcus aureus in patients with cystic fibrosis

Recent reports indicate that methicillin-resistant Staphylococcus aureus (MRSA) may be emerging as a significant pediatric nosocomial pathogen. Children with cystic fibrosis (CF) pulmonary disease are subject to many of the risk factors for MRSA colonization and/or infection. We retrospectively investigated the prevalence and significance of MRSA from sputum and throat cultures in 452 patients with CF followed during 1986. No MRSA had been isolated during 1984 or 1985. Although S. aureus was isolated from 212 patients (47%) in 1986, only 14 (3%) showed MRSA. The MRSA strains had 11 different antimicrobial susceptibility patterns. Neither age, clinical condition, nor recent prior hospitalization correlated with MRSA acquisition. Acquisition did not appear to directly affect the course of the pulmonary disease in these patients even though no patient received any treatment for their MRSA. The prevalence of MRSA is low, although patients with CF are subject to many risk factors. MRSA appears to be mainly community-acquired and to represent colonization rather than infection. However, the potential for nosocomial MRSA infection is present, and vigilance is required in monitoring any changes in frequency of isolation or infection with these organisms.     

2011年医院金黄色葡萄球菌临床分布及耐药性研究

目的调查金黄色葡萄球菌(SA)和耐甲氧西林金黄色葡萄球菌(MRSA)临床分布情况及其对常用抗菌药物的耐药率。方法对我院2011年检出的SA和MRSA药敏结果分析。结果 2011年共检出SA 146株(其中MRSA 29株),菌株主要来源为痰液49株(33.56%),脓液37株(25.34%),泌尿生殖道分泌物11株(7.53%);菌株分布前三位的科室是神经外科36株(24.66%)、创伤外科24株(16.44%)、呼吸消化科17株(11.64%);其中MRSA 29株(19.8%)。分离的146株SA对万古霉素、利奈唑胺全部敏感,其中MRSA对红霉素、克林霉素、四环素和环丙沙星呈现较高的耐药率,达70%以上;MRSA对各种抗生素的耐药率均明显高于MSSA,并呈现多重耐药。结论通过对SA临床分布和耐药率的分析,有利于采取措施控制医院内MR-SA的感染及流行并能指导临床合理用药。     

Aumento significativo de la colonización por Staphylococcus aureus entre los estudiantes de medicina durante la realización de las prácticas en el hospital

Introduction

Staphylococcus aureus is a pathogen of major concern. The emergence of methicillin-resistant S. aureus (MRSA) has increasingly complicated the therapeutic approach of hospital-acquired infections. Surveillance of MRSA and control measures must be implemented in different healthcare settings, including screening programs for carriers. Our first aim was to determine the prevalence of methicillin-susceptible S. aureus (MSSA) and MRSA nasal carriage in medical students from the Clínico San Carlos Hospital (Madrid). As the MRSA carrier rate in healthcare workers is higher than in the general population, we hypothesised that carrier rate could be increased during their clinical practice in their last three years.

Methods

We performed an epidemiologic al study of the prevalence of S. aureus colonisation among a group of medical students, who were sampled in 2008 in their third-year, and in 2012 when this class was in its sixth year.

Results

We have found a significant increase in MSSA carriage, from 27% to 46%. There were no MRSA colonisations in the third-year, but one was found in the sixth-year group. The large majority of strains (89%) of strains were resistant to penicillin, and 27% to erythromycin and clindamycin. As 19 coagulase-negative Staphylococcus MR were also identified, a horizontal transfer of genes, such as mecA gene to S. aureus, could have occurred.

Conclusions

Medical students are both, at risk for acquiring, and a potential source of nosocomial pathogens, mainly MSSA. Therefore, they should take special care for hygienic precautions, such as frequent and proper hand washing, while working in the hospital.     

Emergence of community-associated methicillin-resistant Staphylococcus aureus carriage in children in Cambodia

We previously described the first reported isolation of methicillin-resistant Staphylococcus aureus (MRSA) (a case series of pediatric community-associated MRSA infections) in Cambodia. We define the rate of pediatric MRSA carriage in the same population and characterize the associated bacterial genotypes by using pulsed-field gel electrophoresis and multilocus sequence typing. A prospective cohort study of MRSA carriage conducted over one month at the Angkor Hospital for Children, Siem Reap, Cambodia, identified MRSA carriage in 87 (3.5%) of 2,485 children who came to the outpatient department, and 6 (4.1%) of 145 inpatients, including at least two with cases of nosocomial acquisition. Genotyping of all 93 MRSA isolates resolved 5 genotypes. Most (91%) isolates were assigned to sequence type 834. Only 28 (32%) of 87 MRSA carriers identified in the outpatient department had no history of recent healthcare contact. The study findings have important implications for healthcare in a setting where diagnostic microbiology and access to antimicrobial drugs with efficacy against MRSA are limited.     

Mutations in agr do not persist in natural populations of methicillin-resistant Staphylococcus aureus

Staphylococcus aureus organisms vary in the function of the staphylococcal virulence regulator gene agr. To test for a relationship between agr and transmission in S. aureus, we determined the prevalence and genetic basis of agr dysfunction among nosocomial methicillin-resistant S. aureus (MRSA) in an area of MRSA endemicity. Identical inactivating agr mutations were not detected in epidemiologically unlinked clones within or between hospitals. Additionally, most agr mutants had single mutations, indicating that they were short lived. Collectively, the results suggest that agr dysfunction is adaptive for survival in the infected host but that it may be counteradaptive outside infected host tissues.     

Control of MRSA infection and colonisation in an intensive care unit by GeneOhm MRSA assay and culture methods

Background  

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major nosocomial pathogens. Due to the diffusion of MRSA strains in both hospital and community settings, prevention and control strategies are receiving increased attention. Approximately 25% to 30% of the population is colonised with S. aureus and 0.2% to 7% with MRSA. The BD GeneOhm MRSA real-time PCR assay offers quicker identification of MRSA-colonised patients than do culture methods.     

耐甲氧西林金黄色葡萄球菌检出动态及对万古霉素的耐药性变迁

目的 观察耐甲氧西林金黄色葡萄球菌(MRSA)在临床标本中的检出动态及对万古霉素的耐药性变化趋势。方法 检测1966年～2001年各年度各种临床标本中MRSAR的分离率，测量万古霉素对MRSA的抑菌环直径大小。结果 1996～2000年5年内MRSA检出率有逐年上升趋势，2001年通过筛查MRSA携带者并采取消毒隔离措施后，2001年MRSA检出率为32．1％，与2000年(45．9％)、1999年检出率(38．5％)比较明显降低，与1998年(30．2％)接近。随着时间推移，各年度MRSA对万古霉素的抑菌圈直径逐年减小。结论 通过筛查MRSA携带者并采取严格的消毒隔离措施，可使MRSA的检出率下降。MRSA对万古霉素的敏感程度在逐年降低。