# I. Introduction
Multidrug-resistant organisms(MDROs), including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and certain gram-negative bacilli (GNB) have important infection control implications that either have not been addressed or received only limited consideration in previous isolation guidelines. Increasing experience with these organisms is improving understanding of the routes of transmission and effective preventive measures. Although transmission of MDROs is most frequently documented in acute care facilities, all healthcare settings are affected by the emergence and transmission of antimicrobial-resistant microbes. The severity and extent of disease caused by these pathogens varies by the population(s) affected and by the institution(s) in which they are found. Institutions, in turn, vary widely in physical and functional characteristics, ranging from long-term care facilities (LTCF) to specialty units (e.g., intensive care units , burn units, neonatal ICUs ) in tertiary care facilities. Because of this, the approaches to prevention and control of these pathogens need to be tailored to the specific needs of each population and individual institution. The prevention and control of MDROs is a national priority -one that requires that all healthcare facilities and agencies assume responsibility (1) (2). The following discussion and recommendations are provided to guide the implementation of strategies and practices to prevent the transmission of MRSA, VRE, and other MDROs. The administration of healthcare organizations and institutions should ensure that appropriate strategies are fully implemented, regularly evaluated for effectiveness, and adjusted such that there is a consistent decrease in the incidence of targeted MDROs.
Successful prevention and control of MDROs requires administrative and scientific leadership and a financial and human resource commitment (3)(4)(5). Resources must be made available for infection prevention and control, including expert consultation, laboratory support, adherence monitoring, and data analysis. Infection prevention and control professionals have found that healthcare personnel (HCP) are more receptive and adherent to the recommended control measures when organizational leaders participate in efforts to reduce MDRO transmission (3).

# II. Background

# MDRO definition.
For epidemiologic purposes, MDROs are defined as microorganisms, predominantly bacteria, that are resistant to one or more classes of antimicrobial agents (1).
Although the names of certain MDROs describe resistance to only one agent (e.g., MRSA, VRE), these pathogens are frequently resistant to most available antimicrobial agents .
These highly resistant organisms deserve special attention in healthcare facilities (2). In addition to MRSA and VRE, certain GNB, including those producing extended spectrum beta-lactamases (ESBLs) and others that are resistant to multiple classes of antimicrobial agents, are of particular concern. 1 In addition to Escherichia coli and Klebsiella pneumoniae, these include strains of Acinetobacter baumannii resistant to all antimicrobial agents, or all except imipenem, (6)(7)(8)(9)(10)(11)(12), and organisms such as Stenotrophomonas maltophilia (12)(13)(14), Burkholderia cepacia (15,16), and Ralstonia pickettii (17) that are intrinsically resistant to the broadest-spectrum antimicrobial agents. In some residential settings (e.g., LTCFs), it is important to control multidrug-resistant S. pneumoniae (MDRSP) that are resistant to penicillin and other broad-spectrum agents such as macrolides and fluroquinolones (18,19). Clinical importance of MDROs. In most instances, MDRO infections have clinical manifestations that are similar to infections caused by susceptible pathogens. However, options for treating patients with these infections are often extremely limited. For example, until recently, only vancomycin provided effective therapy for potentially life-threatening MRSA infections and during the 1990's there were virtually no antimicrobial agents to treat infections caused by VRE. Although antimicrobials are now available for treatment of MRSA and VRE infections, resistance to each new agent has already emerged in clinical 1 Multidrug-resistant strains of M. tuberculosis are not addressed in this document because of the markedly different patterns of transmission and spread of the pathogen and the very different control interventions that are needed for prevention of M. tuberculosis infection. Current recommendations for prevention and control of tuberculosis can be found at:  .
isolates (31)(32)(33)(34)(35)(36)(37). Similarly, therapeutic options are limited for ESBL-producing isolates of gram-negative bacilli, strains of A. baumannii resistant to all antimicrobial agents except imipenem (8)(9)(10)(11)38) and intrinsically resistant Stenotrophomonas sp. (12)(13)(14)39). These limitations may influence antibiotic usage patterns in ways that suppress normal flora and create a favorable environment for development of colonization when exposed to potential MDR pathogens (i.e., selective advantage) (40).
Increased lengths of stay, costs, and mortality also have been associated with MDROs (41)(42)(43)(44)(45)(46). Two studies documented increased mortality, hospital lengths of stay, and hospital charges associated with multidrug-resistant gram-negative bacilli (MDR-GNBs), including an NICU outbreak of ESBL-producing Klebsiella pneumoniae (47) and the emergence of thirdgeneration cephalosporin resistance in Enterobacter spp. in hospitalized adults (48).
Vancomycin resistance has been reported to be an independent predictor of death from enterococcal bacteremia (44,(49)(50)(51)(52)(53). Furthermore, VRE was associated with increased mortality, length of hospital stay, admission to the ICU, surgical procedures, and costs when VRE patients were compared with a matched hospital population (54).
However, MRSA may behave differently from other MDROs. When patients with MRSA have been compared to patients with methicillin-susceptible S. aureus (MSSA), MRSAcolonized patients more frequently develop symptomatic infections (55,56). Furthermore, higher case fatality rates have been observed for certain MRSA infections, including bacteremia (57)(58)(59)(60)(61)(62), poststernotomy mediastinitis (63), and surgical site infections (64). These outcomes may be a result of delays in the administration of vancomycin, the relative decrease in the bactericidal activity of vancomycin (65), or persistent bacteremia associated with intrinsic characteristics of certain MRSA strains (66). Mortality may be increased further by S. aureus with reduced vancomycin susceptibility (VISA) (26,67). Also some studies have reported an association between MRSA infections and increased length of stay, and healthcare costs (46,61,62), while others have not (64). Finally, some hospitals have observed an increase in the overall occurrence of staphylococcal infections following the introduction of MRSA into a hospital or special-care unit (68,69).

# III. Epidemiology of MDROs
Trends: Prevalence of MDROs varies temporally, geographically, and by healthcare setting (70,71). For example, VRE emerged in the eastern United States in the early 1990s, but did not appear in the western United States until several years later, and MDRSP varies in prevalence by state (72). The type and level of care also influence the prevalence of MDROs. ICUs, especially those at tertiary care facilities, may have a higher prevalence of MDRO infections than do non-ICU settings (73,74). Antimicrobial resistance rates are also strongly correlated with hospital size, tertiary-level care, and facility type (e.g., LTCF) (75,76). The frequency of clinical infection caused by these pathogens is low in LTCFs (77,78).
Nonetheless, MDRO infections in LTCFs can cause serious disease and mortality, and colonized or infected LTCF residents may serve as reservoirs and vehicles for MDRO introduction into acute care facilities (78)(79)(80)(81)(82)(83)(84)(85)(86)(87)(88). Another example of population differences in prevalence of target MDROs is in the pediatric population. Point prevalence surveys conducted by the Pediatric Prevention Network (PPN) in eight U.S. PICUs and 7 U.S.
NICUs in 2000 found < 4% of patients were colonized with MRSA or VRE compared with 10-24% were colonized with ceftazidime-or aminoglycoside-resistant gram-negative bacilli; < 3% were colonized with ESBL-producing gram negative bacilli. Despite some evidence that MDRO burden is greatest in adult hospital patients, MDRO require similar control efforts in pediatric populations as well (89).
During the last several decades, the prevalence of MDROs in U.S. hospitals and medical centers has increased steadily (90,91). MRSA was first isolated in the United States in 1968. By the early 1990s, MRSA accounted for 20%-25% of Staphylococcus aureus isolates from hospitalized patients (92). In 1999, MRSA accounted for >50% of S. aureus isolates from patients in ICUs in the National Nosocomial Infection Surveillance (NNIS) system; in 2003, 59.5% of S. aureus isolates in NNIS ICUs were MRSA (93). A similar rise in prevalence has occurred with VRE (94). From 1990 to 1997, the prevalence of VRE in enterococcal isolates from hospitalized patients increased from <1% to approximately 15% (95). VRE accounted for almost 25% of enterococcus isolates in NNIS ICUs in 1999 (94), and 28.5% in 2003 (93).
GNB resistant to ESBLs, fluoroquinolones, carbapenems, and aminoglycosides also have increased in prevalence. For example, in 1997, the SENTRY Antimicrobial Surveillance Program found that among K. pneumoniae strains isolated in the United States, resistance rates to ceftazidime and other third-generation cephalosporins were 6.6%, 9.7%, 5.4%, and 3.6% for bloodstream, pneumonia, wound, and urinary tract infections, respectively (95) In 2003, 20.6% of all K. pneumoniae isolates from NNIS ICUs were resistant to these drugs (( 93)). Similarly, between 1999 and 2003, Pseudomonas aeruginosa resistance to fluoroquinolone antibiotics increased from 23% to 29.5% in NNIS ICUs (74). Also, a 3-month survey of 15 Brooklyn hospitals in 1999 found that 53% of A. baumannii strains exhibited resistance to carbapenems and 24% of P. aeruginosa strains were resistant to imipenem (10). During 1994-2000, a national review of ICU patients in 43 states found that the overall susceptibility to ciprofloxacin decreased from 86% to 76% and was temporally associated with increased use of fluoroquinolones in the United States (96).
Lastly, an analysis of temporal trends of antimicrobial resistance in non-ICU patients in 23 U.S. hospitals during 1996-1997 and 1998-1999 (97) found significant increases in the prevalence of resistant isolates including MRSA, ciprofloxacin-resistant P. aeruginosa, and ciprofloxacin-or ofloxacin-resistant E. coli. Several factors may have contributed to these increases including: selective pressure exerted by exposure to antimicrobial agents, particularly fluoroquinolones, outside of the ICU and/or in the community (7,96,98); increasing rates of community-associated MRSA colonization and infection (99,100); inadequate adherence to infection control practices; or a combination of these factors.

# Important concepts in transmission.
Once MDROs are introduced into a healthcare setting, transmission and persistence of the resistant strain is determined by the availability of vulnerable patients, selective pressure exerted by antimicrobial use, increased potential for transmission from larger numbers of colonized or infected patients ("colonization pressure") (101,102); and the impact of implementation and adherence to prevention efforts.
Patients vulnerable to colonization and infection include those with severe disease, especially those with compromised host defenses from underlying medical conditions; recent surgery; or indwelling medical devices (e.g., urinary catheters or endotracheal tubes (103,104)). Hospitalized patients, especially ICU patients, tend to have more risk factors than non-hospitalized patients do, and have the highest infection rates. For example, the risk that an ICU patient will acquire VRE increases significantly once the proportion of ICU patients colonized with VRE exceeds 50% (101) or the number days of exposure to a VRE-patient exceeds 15 days (105). A similar effect of colonization pressure has been demonstrated for MRSA in a medical ICU (102). Increasing numbers of infections with MDROs also have been reported in non-ICU areas of hospitals (97).
There is ample epidemiologic evidence to suggest that MDROs are carried from one person to another via the hands of HCP (106)(107)(108)(109). Hands are easily contaminated during the process of care-giving or from contact with environmental surfaces in close proximity to the patient (110)(111)(112)(113). The latter is especially important when patients have diarrhea and the reservoir of the MDRO is the gastrointestinal tract (114)(115)(116)(117). Without adherence to published recommendations for hand hygiene and glove use (111) HCP are more likely to transmit MDROs to patients. Thus, strategies to increase and monitor adherence are important components of MDRO control programs (106,118).
Opportunities for transmission of MDROs beyond the acute care hospital results from patients receiving care at multiple healthcare facilities and moving between acute-care, ambulatory and/or chronic care, and LTC environments. System-wide surveillance at LDS Hospital in Salt Lake City, Utah, monitored patients identified as being infected or colonized with MRSA or VRE, and found that those patients subsequently received inpatient or outpatient care at as many as 62 different healthcare facilities in that system during a 5-year span (119).

# Role of colonized HCP in MDRO transmission. Rarely, HCP may introduce an MDRO
into a patient care unit (120)(121)(122)(123). Occasionally, HCP can become persistently colonized with an MDRO, but these HCP have a limited role in transmission, unless other factors are present. Additional factors that can facilitate transmission, include chronic sinusitis(120), upper respiratory infection (123), and dermatitis (124).

# Implications of community-associated MRSA (CA-MRSA).
The emergence of new epidemic strains of MRSA in the community, among patients without established MRSA risk factors, may present new challenges to MRSA control in healthcare settings (125)(126)(127)(128).
Historically, genetic analyses of MRSA isolated from patients in hospitals worldwide revealed that a relatively small number of MRSA strains have unique qualities that facilitate their transmission from patient to patient within healthcare facilities over wide geographic areas, explaining the dramatic increases in HAIs caused by MRSA in the 1980s and early 1990s (129). To date, most MRSA strains isolated from patients with CA-MRSA infections have been microbiologically distinct from those endemic in healthcare settings, suggesting that some of these strains may have arisin de novo in the community via acquisition of methicillin resistance genes by established methicillin-susceptible S. aureus (MSSA) strains (130)(131)(132). Two pulsed-field types, termed USA300 and USA400 according to a typing scheme established at CDC, have accounted for the majority of CA-MRSA infections characterized in the United States, whereas pulsed-field types USA100 and USA200 are the predominant genotypes endemic in healthcare settings (133). USA300 and USA400 genotypes almost always carry type IV of the staphylococcal chromosomal cassette (SCC) mec, the mobile genetic element that carries the mecA methicillin-resistance gene (133,134). This genetic cassette is smaller than types I through III, the types typically found in healthcare associated MRSA strains, and is hypothesized to be more easily transferable between S. aureus strains.
CA-MRSA infection presents most commonly as relatively minor skin and soft tissue infections, but severe invasive disease, including necrotizing pneumonia, necrotizing fasciitis, severe osteomyelitis, and a sepsis syndrome with increased mortality have also been described in children and adults (134)(135)(136).
Transmission within hospitals of MRSA strains first described in the community (e.g. USA300 and USA400) are being reported with increasing frequency (137)(138)(139)(140). Changing resistance patterns of MRSA in ICUs in the NNIS system from 1992 to 2003 provide additional evidence that the new epidemic MRSA strains are becoming established healthcare-associated as well as community pathogens (90). Infections with these strains have most commonly presented as skin disease in community settings. However, intrinsic virulence characteristics of the organisms can result in clinical manifestations similar to or potentially more severe than traditional healthcare-associated MRSA infections among hospitalized patients. The prevalence of MRSA colonization and infection in the surrounding community may therefore affect the selection of strategies for MRSA control in healthcare settings.

# IV. MDRO Prevention and Control
Prevention of Infections. Preventing infections will reduce the burden of MDROs in healthcare settings. Prevention of antimicrobial resistance depends on appropriate clinical practices that should be incorporated into all routine patient care. These include optimal management of vascular and urinary catheters, prevention of lower respiratory tract infection in intubated patients, accurate diagnosis of infectious etiologies, and judicious antimicrobial selection and utilization. Guidance for these preventive practices include the Campaign to Reduce Antimicrobial Resistance in Healthcare Settings (www.cdc.gov/drugresistance/healthcare/default.htm), a multifaceted, evidence-based approach with four parallel strategies: infection prevention; accurate and prompt diagnosis and treatment; prudent use of antimicrobials; and prevention of transmission. Campaign materials are available for acute care hospitals, surgical settings, dialysis units, LTCFs and pediatric acute care units.
To reduce rates of central-venous-line associated bloodstream infections(CVL-BSIs) and ventilator-associated pneumonia (VAP), a group of bundled evidence-based clinical practices have been implemented in many U.S. healthcare facilities (118,(141)(142)(143)(144). One report demonstrated a sustained effect on the reduction in CVL-BSI rates with this approach (145). Although the specific effect on MDRO infection and colonization rates have not been reported, it is logical that decreasing these and other healthcare-associated infections will in turn reduce antimicrobial use and decrease opportunities for emergence and transmission of MDROs.

# Prevention and Control of MDRO transmission
Overview of the MDRO control literature. Successful control of MDROs has been documented in the United States and abroad using a variety of combined interventions.
These include improvements in hand hygiene, use of Contact Precautions until patients are culture-negative for a target MDRO, active surveillance cultures (ASC), education, enhanced environmental cleaning, and improvements in communication about patients with MDROs within and between healthcare facilities.

# Representative studies include:
Reduced rates of MRSA transmission in The Netherlands, Belgium, Denmark, and other Scandinavian countries after the implementation of aggressive and sustained infection control interventions (i.e., ASC; preemptive use of Contact Precautions upon admission until proven culture negative; and, in some instances, closure of units to new admissions). MRSA generally accounts for a very small proportion of S. aureus clinical isolates in these countries (146)(147)(148)(149)(150).
Reduced rates of VRE transmission in healthcare facilities in the three-state Siouxland region (Iowa, Nebraska, and South Dakota) following formation of a coalition and development of an effective region-wide infection control intervention that included ASC and isolation of infected patients. The overall prevalence rate of VRE in the 30 participating facilities decreased from 2.2% in 1997 to 0.5% in 1999 (151).
Eradication of endemic MRSA infections from two NICUs. The first NICU included implementation of ASC, Contact Precautions, use of triple dye on the umbilical cord, and systems changes to improve surveillance and adherence to recommended practices and to reduce overcrowding (152). The second NICU used ASC and Contact Precautions; surgical masks were included in the barriers used for Contact Precautions (153).
Control of an outbreak and eventual eradication of VRE from a burn unit over a 13month period with implementation of aggressive culturing, environmental cleaning, and barrier isolation (154).
Control of an outbreak of VRE in a NICU over a 3-year period with implementation of ASC, other infection control measures such as use of a waterless hand disinfectant, and mandatory in-service education (155).
Eradication of MDR-strains of A. baumannii from a burn unit over a 16-month period with implementation of strategies to improve adherence to hand hygiene, isolation, environmental cleaning, and temporary unit closure (38).
In addition, more than 100 reports published during 1982-2005 support the efficacy of combinations of various control interventions to reduce the burden of MRSA, VRE, and MDR-GNBs (Tables 1 and 2). Case-rate reduction or pathogen eradication was reported in a majority of studies.
VRE was eradicated in seven special-care units (154,(156)(157)(158)(159)(160), two hospitals (161,162), and one LTCF (163).
MRSA was eradicated from nine special-care units (89,152,153,(164)(165)(166)(167)(168)(169), two hospitals (170), one LTCF(167), and one Finnish district (171). Furthermore, four MRSA reports described continuing success in sustaining low endemic MDRO rates for over 5 years (68,166,172,173).
An MDR-GNB was eradicated from 13 special-care units (8,9,38,(174)(175)(176)(177)(178)(179)(180) and two hospitals (11,181).
These success stories testify to the importance of having dedicated and knowledgeable teams of healthcare professionals who are willing to persist for years, if necessary, to control MDROs. Eradication and control of MDROs, such as those reported, frequently required periodic reassessment and the addition of new and more stringent interventions over time (tiered strategy). For example, interventions were added in a stepwise fashion during a 3-year effort that eventually eradicated MRSA from an NICU (152). A series of interventions was adopted throughout the course of a year to eradicate VRE from a burn unit (154). Similarly, eradication of carbapenem-resistant strains of A. baumannii from a hospital required multiple and progressively more intense interventions over several years (11).
Nearly all studies reporting successful MDRO control employed a median of 7 to 8 different interventions concurrently or sequentially (Table 1). These figures may underestimate the actual number of control measures used, because authors of these reports may have considered their earliest efforts routine (e.g., added emphasis on handwashing), and did not include them as interventions, and some "single measures" are, in fact, a complex combination of several interventions. The use of multiple concurrent control measures in these reports underscores the need for a comprehensive approach for controlling MDROs.
Several factors affect the ability to generalize the results of the various studies reviewed, including differences in definition, study design, endpoints and variables measured, and period of follow-up. Two-thirds of the reports cited in Tables 1 and 2 involved perceived outbreaks, and one-third described efforts to reduce endemic transmission. Few reports described preemptive efforts or prospective studies to control MDROs before they had reached high levels within a unit or facility.
With these and other factors, it has not been possible to determine the effectiveness of individual interventions, or a specific combination of interventions, that would be appropriate for all healthcare facilities to implement in order to control their target MDROs. Randomized controlled trials are necessary to acquire this level of evidence. An NIH-sponsored, randomized controlled trial on the prevention of MRSA and VRE transmission in adult ICUs is ongoing and may provide further insight into optimal control measures (). This trial compares the use of education (to improve adherence to hand hygiene) and Standard Precautions to the use of ASC and Contact Precautions.

# Control Interventions. The various types of interventions used to control or eradicate
MDROs may be grouped into seven categories. These include administrative support, judicious use of antimicrobials, surveillance (routine and enhanced), Standard and Contact Precautions, environmental measures, education and decolonization. These interventions provide the basis for the recommendations for control of MDROs in healthcare settings that follow this review and as summarized in Table 3. In the studies reviewed, these interventions were applied in various combinations and degrees of intensity, with differences in outcome.

# Administrative support.
In several reports, administrative support and involvement were important for the successful control of the target MDRO (3,152,(182)(183)(184)(185), and authorities in infection control have strongly recommended such support (2,106,107,186). There are several examples of MDRO control interventions that require administrative commitment of fiscal and human resources. One is the use of ASC (8,38,68,107,114,151,152,167,168,183,184,(187)(188)(189)(190)(191)(192). Other interventions that require administrative support include: 1) implementing system changes to ensure prompt and effective communications e.g., computer alerts to identify patients previously known to be colonized/infected with MDROs (184,189,193,194); 2), providing the necessary number and appropriate placement of hand washing sinks and alcohol-containing hand rub dispensers in the facility (106,195); 3) maintaining staffing levels appropriate to the intensity of care required (152,(196)(197)(198)(199)(200)(201)(202); and 4) enforcing adherence to recommended infection control practices (e.g., hand hygiene, Standard and Contact Precautions) for MDRO control. Other measures that have been associated with a positive impact on prevention efforts, that require administrative support, are direct observation with feedback to HCP on adherence to recommended precautions and keeping HCP informed about changes in transmission rates (3,152,182,(203)(204)(205). A "How-to guide" for implementing change in ICUs, including analysis of structure, process, and outcomes when designing interventions, can assist in identification of needed administrative interventions (195).
Lastly, participation in existing, or the creation of new, city-wide, state-wide, regional or national coalitions, to combat emerging or growing MDRO problems is an effective strategy that requires administrative support (146,151,167,188,206,207).

# Education.
Facility-wide, unit-targeted, and informal, educational interventions were included in several successful studies (3,189,193,(208)(209)(210)(211). The focus of the interventions was to encourage a behavior change through improved understanding of the problem MDRO that the facility was trying to control. Whether the desired change involved hand hygiene, antimicrobial prescribing patterns, or other outcomes, enhancing understanding and creating a culture that supported and promoted the desired behavior, were viewed as essential to the success of the intervention.
Educational campaigns to enhance adherence to hand hygiene practices in conjunction with other control measures have been associated temporally with decreases in MDRO transmission in various healthcare settings (3,106,163).

# Judicious use of antimicrobial agents.
While a comprehensive review of antimicrobial stewardship is beyond the scope of this guideline, recommendations for control of MDROs must include attention to judicious antimicrobial use. A temporal association between formulary changes and decreased occurrence of a target MDRO was found in several studies, especially in those that focused on MDR-GNBs (98,177,209,(212)(213)(214)(215)(216)(217)(218). Occurrence of C. difficile-associated disease has also been associated with changes in antimicrobial use (219). Although some MRSA and VRE control efforts have attempted to limit antimicrobial use, the relative importance of this measure for controlling these MDROs remains unclear (193,220). Limiting antimicrobial use alone may fail to control resistance due to a combination of factors; including 1) the relative effect of antimicrobials on providing initial selective pressure, compared to perpetuating resistance once it has emerged; 2) inadequate limits on usage; or 3) insufficient time to observe the impact of this intervention. With the intent of addressing #2 and #3 above in the study design, one study demonstrated a decrease in the prevalence of VRE associated with a formulary switch from ticarcillinclavulanate to piperacillin-tazobactam (221).
The CDC Campaign to Prevent Antimicrobial Resistance that was launched in 2002 provides evidence-based principles for judicious use of antimicrobials and tools for implementation (222) www.cdc.gov/drugresistance/healthcare. This effort targets all healthcare settings and focuses on effective antimicrobial treatment of infections, use of narrow spectrum agents, treatment of infections and not contaminants, avoiding excessive duration of therapy, and restricting use of broad-spectrum or more potent antimicrobials to treatment of serious infections when the pathogen is not known or when other effective agents are unavailable. Achieving these objectives would likely diminish the selective pressure that favors proliferation of MDROs. Strategies for influencing antimicrobial prescribing patterns within healthcare facilities include education; formulary restriction; prior-approval programs, including pre-approved indications; automatic stop orders; academic interventions to counteract pharmaceutical influences on prescribing patterns; antimicrobial cycling (223)(224)(225)(226); computer-assisted management programs (227)(228)(229); and active efforts to remove redundant antimicrobial combinations (230). A systematic review of controlled studies identified several successful practices. These include social marketing (i.e. consumer education), practice guidelines, authorization systems, formulary restriction, mandatory consultation, and peer review and feedback. It further suggested that online systems that provide clinical information, structured order entry, and decision support are promising strategies (231). These changes are best accomplished through an organizational, multidisciplinary, antimicrobial management program(232).

# Surveillance for MDROs isolated from routine clinical cultures.
Antibiograms. The simplest form of MDRO surveillance is monitoring of clinical microbiology isolates resulting from tests ordered as part of routine clinical care. This method is particularly useful to detect emergence of new MDROs not previously detected, either within an individual healthcare facility or community-wide. In addition, this information can be used to prepare facility-or unit-specific summary antimicrobial susceptibility reports that describe pathogen-specific prevalence of resistance among clinical isolates. Such reports may be useful to monitor for changes in known resistance patterns that might signal emergence or transmission of MDROs, and also to provide clinicians with information to guide antimicrobial prescribing practices (233)(234)(235).

# MDRO Incidence Based on Clinical Culture
Results. Some investigators have used clinical microbiology results to calculate measures of incidence of MDRO isolates in specific populations or patient care locations (e.g. new MDRO isolates/1,000 patient days, new MDRO isolates per month) (205,236,237). Such measures may be useful for monitoring MDRO trends and assessing the impact of prevention programs, although they have limitations. Because they are based solely on positive culture results without accompanying clinical information, they do not distinguish colonization from infection, and may not fully demonstrate the burden of MDRO-associated disease. Furthermore, these measures do not precisely measure acquisition of MDRO colonization in a given populaton or location. Isolating an MDRO from a clinical culture obtained from a patient several days after admission to a given unit or facility does not establish that the patient acquired colonization in that unit. On the other hand, patients who acquire MDRO colonization may remain undetected by clinical cultures (107). Despite these limitations, incidence measures based on clinical culture results may be highly correlated with actual MDRO transmission rates derived from information using ASC, as demonstrated in a recent multicenter study (237). These results suggest that incidence measures based on clinical cultures alone might be useful surrogates for monitoring changes in MDRO transmission rates.

# MDRO Infection Rates.
Clinical cultures can also be used to identify targeted MDRO infections in certain patient populations or units (238,239). This strategy requires investigation of clinical circumstances surrounding a positive culture to distinguish colonization from infection, but it can be particularly helpful in defining the clinical impact of MDROs within a facility.

# Molecular typing of MDRO isolates. Many investigators have used molecular
typing of selected isolates to confirm clonal transmission to enhance understanding of MDRO transmission and the effect of interventions within their facility (38,68,89,92,138,152,190,193,236,240).

# Surveillance for MDROs by Detecting Asymptomatic Colonization
Another form of MDRO surveillance is the use of active surveillance cultures (ASC) to identify patients who are colonized with a targeted MDRO (38,107,241). This approach is based upon the observation that, for some MDROs, detection of colonization may be delayed or missed completely if culture results obtained in the course of routine clinical care are the primary means of identifying colonized patients (8,38,107,114,151,153,167,168,183,184,187,189,(191)(192)(193)(242)(243)(244).
Several authors report having used ASC when new pathogens emerge in order to define the epidemiology of the particular agent (22,23,107,190). In addition, the authors of several reports have concluded that ASC, in combination with use of Contact Precautions for colonized patients, contributed directly to the decline or eradication of the target MDRO (38,68,107,151,153,184,217,242). However, not all studies have reached the same conclusion. Poor control of MRSA despite use of ASC has been described (245). A recent study failed to identify cross-transmission of MRSA or MSSA in a MICU during a 10 week period when ASC were obtained, despite the fact that culture results were not reported to the staff (246). The investigators suggest that the degree of cohorting and adherence to Standard Precautions might have been the important determinants of transmission prevention, rather than the use of ASC and Contact Precautions for MRSA-colonized patients.
The authors of a systematic review of the literature on the use of isolation measures to control healthcare-associated MRSA concluded that there is evidence that concerted efforts that include ASC and isolation can reduce MRSA even in endemic settings. However, the authors also noted that methodological weaknesses and inadequate reporting in published research make it difficult to rule out plausible alternative explanations for reductions in MRSA acquisition associated with these interventions, and therefore concluded that the precise contribution of active surveillance and isolation alone is difficult to assess (247).
Mathematical modeling studies have been used to estimate the impact of ASC use in control of MDROs. One such study evaluating interventions to decrease VRE transmission indicated that use of ASC (versus no cultures) could potentially decrease transmission 39% and that with pre-emptive isolation plus ASC, transmission could be decreased 65% (248). Another mathematical model examining the use of ASC and isolation for control of MRSA predicted that isolating colonized or infected patients on the basis of clinical culture results is unlikely to be successful at controlling MRSA, whereas use of active surveillance and isolation can lead to successful control, even in settings where MRSA is highly endemic.( 249) There is less literature on the use of ASC in controlling MDR-GNBs. Active surveillance cultures have been used as part of efforts to successful control of MDR-GNBs in outbreak settings. The experience with ASC as part of successful control efforts in endemic settings is mixed. One study reported successful reduction of extendedspectrum beta-lactamase -producing Enterobacteriaceae over a six year period using a multifaceted control program that included use of ASC (245). Other reports suggest that use of ASC is not necessary to control endemic MDR-GNBs. (250,251).
More research is needed to determine the circumstances under which ASC are most beneficial( 252), but their use should be considered in some settings, especially if other control measures have been ineffective. When use of ASC is incorporated into MDRO prevention programs, the following should be considered:
- The decision to use ASC as part of an infection prevention and control program requires additional support for successful implementation, including: 1) personnel to obtain the appropriate cultures, 2) microbiology laboratory personnel to process the cultures, 3) mechanism for communicating results to caregivers, 4) concurrent decisions about use of additional isolation measures triggered by a positive culture (e.g. Contact Precautions) and 5) mechanism for assuring adherence to the additional isolation measures.
- The populations targeted for ASC are not well defined and vary among published reports. Some investigators have chosen to target specific patient populations considered at high risk for MDRO colonization based on factors such as location (e.g. ICU with high MDRO rates), antibiotic exposure history, presence of underlying diseases, prolonged duration of stay, exposure to other MDROcolonized patients, patients transferred from other facilities known to have a high prevalence of MDRO carriage, or having a history of recent hospital or nursing home stays (107,151,253). A more commonly employed strategy involves obtaining surveillance cultures from all patients admitted to units experiencing high rates of colonization/infection with the MDROs of interest, unless they are already known to be MDRO carriers (153,184,242,254). In an effort to better define target populations for active surveillance, investigators have attempted to create prediction rules to identify subpopulations of patients at high risk for colonization on hospital admission (255,256). Decisions about which populations should be targeted for active surveillance should be made in the context of local determinations of the incidence and prevalence of MDRO colonization within the intervention facility as well as other facilities with whom patients are frequently exchanged (257).
- Optimal timing and interval of ASC are not well defined. In many reports, cultures were obtained at the time of admission to the hospital or intervention unit or at the time of transfer to or from designated units (e.g., ICU)(107). In addition, some hospitals have chosen to obtain cultures on a periodic basis [e.g., weekly (8,153,159)  o MDR-GNBs: Several methods for detection of MDR-GNBs have been employed, including use of peri-rectal or rectal swabs alone or in combination with oro-pharyngeal, endotracheal, inguinal, or wound cultures. The absence of standardized screening media for many gram-negative bacilli can make the process of isolating a specific MDR-GNB a relatively labor-intensive process (38,190,241,250 (268). The impact of rapid testing on the effectiveness of active surveillance as a prevention strategy, however, has not been fully determined. Rapid identification of MRSA in one study was associated with a significant reduction in MRSA infections acquired in the medical ICU, but not the surgical ICU (265). A mathematical model characterizing MRSA transmission dynamics predicted that, in comparison to conventional culture methods, the use of rapid detection tests may decrease isolation needs in settings of low-endemicity and result in more rapid reduction in prevalence in highly-endemic settings(249).
- Some MDRO control reports described surveillance cultures of healthcare personnel during outbreaks, but colonized or infected healthcare personnel are rarely the source of ongoing transmission, and this strategy should be reserved for settings in which specific healthcare personnel have been epidemiologically implicated in the transmission of MDROs (38,92,(152)(153)(154)188). without ASC, for control of MDROs. Some reports mention the use of one or both sets of precautions as part of successful MDRO control efforts; however, the precautions were not the primary focus of the study intervention (164,190,205,(269)(270)(271). The NIH-sponsored study mentioned earlier (Section: Overview of the MDRO control literature) may provide some answers, ). MDRO control efforts frequently involved changes in isolation practices, especially during outbreaks. In the majority of reports, Contact Precautions were implemented for all patients found to be colonized or infected with the target MDRO (See Table 2). Some facilities also preemptively used Contact Precautions, in conjunction with ASC, for all new admissions or for all patients admitted to a specific unit, until a negative screening culture for the target MDRO was reported (30,184,273).

# Infection Control

# Standard
Contact Precautions are intended to prevent transmission of infectious agents, including epidemiologically important microorganisms, which are transmitted by direct or indirect contact with the patient or the patient's environment. A single-patient room is preferred for patients who require Contact Precautions. When a single-patient room is not available, consultation with infection control is necessary to assess the various risks associated with other patient placement options (e.g., cohorting, keeping the patient with an existing roommate). HCP caring for patients on Contact Precautions should wear a gown and gloves for all interactions that may involve contact with the patient or potentially contaminated areas in the patient's environment. Donning gown and gloves upon room entry and discarding before exiting the patient room is done to contain pathogens, especially those that have been implicated in transmission through environmental contamination (e.g., VRE, C. difficile, noroviruses and other intestinal tract agents; RSV) (109,111,(274)(275)(276)(277).
Cohorting and other MDRO control strategies. In several reports, cohorting of patients (152,153,167,183,184,188,189,217,242), cohorting of staff (184,217,242,278), use of designated beds or units (183,184), and even unit closure (38,146,159,161,279,280) were necessary to control transmission. Some authors indicated that implementation of the latter two strategies were the turning points in their control efforts; however, these measures usually followed many other actions to prevent transmission. In one, two-center study, moving MRSA-positive patients into single rooms or cohorting these patients in designated bays failed to reduce transmission in ICUs. However, in this study adherence to recommendations for hand hygiene between patient contacts was only 21% (281). Other published studies, including one commissioned by the American Institute of Architects and the Facility Guidelines Institute (www.aia.org/aah_gd_hospcons), have documented a beneficial relationship between private rooms and reduction in risk of acquiring MDROs (282). Additional studies are needed to define the specific contribution of using single-patient rooms and/or cohorting on preventing transmission of MDROs.

# Duration of Contact Precautions. The necessary duration of Contact Precautions
for patients treated for infection with an MDRO, but who may continue to be colonized with the organism at one or more body sites, remains an unresolved issue.
Patients may remain colonized with MDROs for prolonged periods; shedding of these organisms may be intermittent, and surveillance cultures may fail to detect their presence (84,250,283). The 1995 HICPAC guideline for preventing the transmission of VRE suggested three negative stool/perianal cultures obtained at weekly intervals as a criterion for discontinuation of Contact Precautions (274). One study found these criteria generally reliable (284). However, this and other studies have noted a recurrence of VRE positive cultures in persons who subsequently receive antimicrobial therapy and persistent or intermittent carriage of VRE for more than 1 year has been reported (284)(285)(286). Similarly, colonization with MRSA can be prolonged (287,288). Studies demonstrating initial clearance of MRSA following decolonization therapy have reported a high frequency of subsequent carriage (289,290). There is a paucity of information in the literature on when to discontinue Contact Precautions for patients colonized with a MDR-GNB, possibly because infection and colonization with these MDROs are often associated with outbreaks.
Despite the uncertainty about when to discontinue Contact Precautions, the studies offer some guidance. In the context of an outbreak, prudence would dictate that Contact Precautions be used indefinitely for all previously infected and known colonized patients. Likewise, if ASC are used to detect and isolate patients colonized with MRSA or VRE, and there is no decolonization of these patients, it is logical to assume that Contact Precautions would be used for the duration of stay in the setting where they were first implemented. In general, it seems reasonable to discontinue Contact Precautions when three or more surveillance cultures for the target MDRO are repeatedly negative over the course of a week or two in a patient who has not received antimicrobial therapy for several weeks, especially in the absence of a draining wound, profuse respiratory secretions, or evidence implicating the specific patient in ongoing transmission of the MDRO within the facility.

# Barriers used for contact with patients infected or colonized with MDROs.
Three studies evaluated the use of gloves with or without gowns for all patient contacts to prevent VRE acquisition in ICU settings (30,105,273). Two of the studies showed that use of both gloves and gowns reduced VRE transmission (30,105) while the third showed no difference in transmission based on the barriers used (273). One study in a LTCF compared the use of gloves only, with gloves plus contact isolation, for patients with four MDROs, including VRE and MRSA, and found no difference (86). However, patients on contact isolation were more likely to acquire MDR-K. pneumoniae strains that were prevalent in the facility; reasons for this were not specifically known. In addition to differences in outcome, differing methodologies make comparisons difficult. Specifically, HCP adherence to the recommended protocol, the influence of added precautions on the number of HCP-patient interactions, and colonization pressure were not consistently assessed.

# Impact of Contact Precautions on patient care and well-being.
There are limited data regarding the impact of Contact Precautions on patients. Two studies found that HCP, including attending physicians, were half as likely to enter the rooms of(291), or examine (292), patients on Contact Precautions. Other investigators have reported similar observations on surgical wards (293). Two studies reported that patients in private rooms and on barrier precautions for an MDRO had increased anxiety and depression scores (294,295). Another study found that patients placed on Contact Precautions for MRSA had significantly more preventable adverse events, expressed greater dissatisfaction with their treatment, and had less documented care than control patients who were not in isolation (296). Therefore, when patients are placed on Contact Precautions, efforts must be made by the healthcare team to counteract these potential adverse effects.

# Environmental measures.
The potential role of environmental reservoirs, such as surfaces and medical equipment, in the transmission of VRE and other MDROs has been the subject of several reports (109-111, 297, 298). While environmental cultures are not routinely recommended (299), environmental cultures were used in several studies to document contamination, and led to interventions that included the use of dedicated noncritical medical equipment (217,300), assignment of dedicated cleaning personnel to the affected patient care unit (154), and increased cleaning and disinfection of frequently-touched surfaces (e.g., bedrails, charts, bedside commodes, doorknobs). A common reason given for finding environmental contamination with an MDRO was the lack of adherence to facility procedures for cleaning and disinfection. In an educational and observational intervention, which targeted a defined group of housekeeping personnel, there was a persistent decrease in the acquisition of VRE in a medical ICU (301). Therefore, monitoring for adherence to recommended environmental cleaning practices is an important determinant for success in controlling transmission of MDROs and other pathogens in the environment (274,302).
In the MDRO reports reviewed, enhanced environmental cleaning was frequently undertaken when there was evidence of environmental contamination and ongoing transmission. Rarely, control of the target MDRO required vacating a patient care unit for complete environmental cleaning and assessment (175,279).

# Decolonization. Decolonization entails treatment of persons colonized with a
specific MDRO, usually MRSA, to eradicate carriage of that organism. Although some investigators have attempted to decolonize patients harboring VRE(220), few have achieved success. However, decolonization of persons carrying MRSA in their nares has proved possible with several regimens that include topical mupirocin alone or in combination with orally administered antibiotics (e.g., rifampin in combination with trimethoprim-sulfamethoxazole or ciprofloxacin) plus the use of an antimicrobial soap for bathing (303). In one report, a 3-day regimen of baths with povidone-iodine and nasal therapy with mupirocin resulted in eradication of nasal MRSA colonization (304). These and other methods of MRSA decolonization have been thoroughly reviewed. (303,(305)(306)(307).
Decolonization regimens are not sufficiently effective to warrant routine use. Therefore, most healthcare facilities have limited the use of decolonization to MRSA outbreaks, or other high prevalence situations, especially those affecting special-care units. Several factors limit the utility of this control measure on a widespread basis: 1) identification of candidates for decolonization requires surveillance cultures; 2) candidates receiving decolonization treatment must receive follow-up cultures to ensure eradication; and 3) recolonization with the same strain, initial colonization with a mupirocin-resistant strain, and emergence of resistance to mupirocin during treatment can occur (289,303,(308)(309)(310). HCP implicated in transmission of MRSA are candidates for decolonization and should be treated and culture negative before returning to direct patient care. In contrast, HCP who are colonized with MRSA, but are asymptomatic, and have not been linked epidemiologically to transmission, do not require decolonization.

# IV. Discussion
This review demonstrates the depth of published science on the prevention and control of MDROs. Using a combination of interventions, MDROs in endemic, outbreak, and nonendemic settings have been brought under control. However, despite the volume of literature, an appropriate set of evidence-based control measures that can be universally applied in all healthcare settings has not been definitively established. This is due in part to differences in study methodology and outcome measures, including an absence of randomized, controlled trials comparing one MDRO control measure or strategy with another. Additionally, the data are largely descriptive and quasi-experimental in design (311). Few reports described preemptive efforts or prospective studies to control MDROs before they had reached high levels within a unit or facility. Furthermore, small hospitals and LTCFs are infrequently represented in the literature.
A number of questions remain and are discussed below.

# Impact on other MDROS from interventions targeted to one MDRO Only one report
described control efforts directed at more than one MDRO, i.e., MDR-GNB and MRSA (312).
Several reports have shown either decreases or increases in other pathogens with efforts to control one MDRO. For example, two reports on VRE control efforts demonstrated an increase in MRSA following the prioritization of VRE patients to private rooms and cohort beds (161). Similarly an outbreak of Serratia marcescens was temporally associated with a concurrent, but unrelated, outbreak of MRSA in an NICU (313). In contrast, Wright and colleagues reported a decrease in MRSA and VRE acquisition in an ICU during and after their successful effort to eradicate an MDR-strain of A. baumannii from the unit (210).
Colonization with multiple MDROs appears to be common (314,315). One study found that nearly 50% of residents in a skilled-care unit in a LTCF were colonized with a target MDRO and that 26% were co-colonized with >1 MDRO; a detailed analysis showed that risk factors for colonization varied by pathogen (316). One review of the literature(317) reported that patient risk factors associated with colonization with MRSA, VRE, MDR-GNB, C. difficile and Candida sp were the same. This review concluded that control programs that focus on only one organism or one antimicrobial drug are unlikely to succeed because vulnerable patients will continue to serve as a magnet for other MDROs.
Costs. Several authors have provided evidence for the cost-effectiveness of approaches that use ASC (153,191,253,318,319). However, the supportive evidence often relied on assumptions, projections, and estimated attributable costs of MDRO infections. Similar limitations apply to a study suggesting that gown use yields a cost benefit in controlling transmission of VRE in ICUs(320). To date, no studies have directly compared the benefits and costs associated with different MDRO control strategies.
Feasibility. The subject of feasibility, as it applies to the extrapolation of results to other healthcare settings, has not been addressed. For example, smaller hospitals and LTCFs may lack the on-site laboratory services needed to obtain ASC in a timely manner. This factor could limit the applicability of an aggressive program based on obtaining ASC and preemptive placement of patients on Contact Precautions in these settings. However, with the growing problem of antimicrobial resistance, and the recognized role of all healthcare settings for control of this problem, it is imperative that appropriate human and fiscal resources be invested to increase the feasibility of recommended control strategies in every setting.

# Factors that influence selection of MDRO control measures.
Although some common principles apply, the preceding literature review indicates that no single approach to the control of MDROs is appropriate for all healthcare facilities. Many factors influence the choice of interventions to be applied within an institution, including: - Population and healthcare-settings. The presence of high-risk patients (e.g., transplant, hematopoietic stem-cell transplant) and special-care units (e.g. adult, pediatric, and neonatal ICUs; burn; hemodialysis) will influence surveillance needs and could limit the areas of a facility targeted for MDRO control interventions. Although it appears that MDRO transmission seldom occurs in ambulatory and outpatient settings, some patient populations (e.g., hemodialysis, cystic fibrosis) and patients receiving chemotherapeutic agents are at risk for colonization and infection with MDROs. Furthermore, the emergence of VRSA within the outpatient setting (22,23,25) demonstrates that even these settings need to make MDRO prevention a priority.

# Differences of opinion on the optimal strategy to control MDROs. Published guidance on the control of MDROs reflects areas of ongoing debate on optimal control strategies.
A key issue is the use of ASC in control efforts and preemptive use of Contact Precautions pending negative surveillance culture results (107,321,322). The various guidelines currently available exhibit a spectrum of approaches, which their authors deem to be evidence-based. One guideline for control of MRSA and VRE, the Society for Healthcare measures that fit their circumstances and needs. Most studies have been in acute care settings; for non-acute care settings (e.g., LCTF, small rural hospitals), the optimal approach is not well defined. 3). As a rule, these reports indicate that facilities confronted with an MDRO problem selected a combination of control measures, implemented them, and reassessed their impact. In some cases, new measures were added serially to further enhance control efforts. This evidence indicates that the control of MDROs is a dynamic process that requires a systematic approach tailored to the problem and healthcare setting.

# Two-Tiered Approach for Control of MDROs. Reports describing successful control of MDRO transmission in healthcare facilities have included seven categories of interventions (Table
The nature of this evidence gave rise to the two-tiered approach to MDRO control recommended in this guideline. This approach provides the flexibility needed to prevent and control MDRO transmission in every kind of facility addressed by this guideline.
Detailed recommendations for MDRO control in all healthcare settings follow and are summarized in Table 3. Table 3, which applies to all healthcare settings, contains two tiers of activities. In the first tier are the baseline level of MDRO control activities designed to ensure recognition of MDROs as a problem, involvement of healthcare administrators, and provision of safeguards for managing unidentified carriers of MDROs.
With the emergence of an MDRO problem that cannot be controlled with the basic set of infection control measures, additional control measures should be selected from the second tier of interventions presented in Table 3. Decisions to intensify MDRO control activity arise from surveillance observations and assessments of the risk to patients in various settings.
Circumstances that may trigger these decisions include:
- Identification of an MDRO from even one patient in a facility or special unit with a highly vulnerable patient population (e.g., an ICU, NICU, burn unit) that had previously not encountered that MDRO.
- Failure to decrease the prevalence or incidence of a specific MDRO (e.g., incidence of resistant clinical isolates) despite infection control efforts to stop its transmission.(Statistical process control charts or other validated methods that account for normal variation can be used to track rates of targeted MDROs) (205,325,326).
The combination of new or increased frequency of MDRO isolates and patients at risk necessitates escalation of efforts to achieve or re-establish control, i.e., to reduce rates of transmission to the lowest possible level. Intensification of MDRO control activities should begin with an assessment of the problem and evaluation of the effectiveness of measures in current use. Once the problem is defined, appropriate additional control measures should be selected from the second tier of Table 3. A knowledgeable infection prevention and control professional or healthcare epidemiologist should make this determination. This approach requires support from the governing body and medical staff of the facility. Once interventions are implemented, ongoing surveillance should be used to determine whether selected control measures are effective and if additional measures or consultation are indicated. The result of this process should be to decrease MDRO rates to minimum levels. Healthcare facilities must not accept ongoing MDRO outbreaks or high endemic rates as the status quo. With selection of infection control measures appropriate to their situation, all facilities can achieve the desired goal and reduce the MDRO burden substantially.

# V. Prevention of transmission of Multidrug Resistant Organisms
(Table 3)
The CDC/HICPAC system for categorizing recommendations is as follows:
Category IA Strongly recommended for implementation and strongly supported by welldesigned experimental, clinical, or epidemiologic studies.
Category IB Strongly recommended for implementation and supported by some experimental, clinical, or epidemiologic studies and a strong theoretical rationale.
Category IC Required for implementation, as mandated by federal and/or state regulation or standard.
Category II Suggested for implementation and supported by suggestive clinical or epidemiologic studies or a theoretical rationale.
No recommendation Unresolved issue. Practices for which insufficient evidence or no consensus regarding efficacy exists.
V.A. General recommendations for all healthcare settings independent of the prevalence of multidrug resistant organism (MDRO) infections or the population served.   (8, 11, 38, 68, 114, 152-154, 183-185, 189, 190, 193, 194, 209, 217, 242, 312, 364, 365). Category IB  (152,153,183,184,189,190,193,205,215,242,365). Category IB Cohorting. In the context of this guideline, this term applies to the practice of grouping patients infected or colonized with the same infectious agent together to confine their care to one area and prevent contact with susceptible patients (cohorting patients). During outbreaks, healthcare personnel may be assigned to a cohort of patients to further limit opportunities for transmission (cohorting staff). o Difficult to treat because of innate or acquired resistance to multiple classes of antimicrobial agents (e.g., Stenotrophomonas maltophilia, Acinetobacter spp.).

# Contact
3) Associated with serious clinical disease, increased morbidity and mortality (e.g., MRSA and MSSA, group A streptococcus); or 4) A newly discovered or reemerging pathogen. The strategies described for MDROs may be applied for control of epidemiologically important organisms other than MDROs.

# Hand hygiene.
A general term that applies to any one of the following: 1) handwashing with plain (nonantimicrobial) soap and water); 2) antiseptic hand wash (soap containing antiseptic agents and water); 3) antiseptic hand rub (waterless antiseptic product, most often alcohol-based, rubbed on all surfaces of hands); or 4) surgical hand antisepsis (antiseptic hand wash or antiseptic hand rub performed preoperatively by surgical personnel to eliminate transient hand flora and reduce resident hand flora).

# Healthcare-associated infection (HAI).
An infection that develops in a patient who is cared for in any setting where healthcare is delivered (e.g., acute care hospital, chronic care facility, ambulatory clinic, dialysis center, surgicenter, home) and is related to receiving health care (i.e., was not incubating or present at the time healthcare was provided). In ambulatory and home settings, HAI would apply to any infection that is associated with a medical or surgical intervention performed in those settings.

# Healthcare personnel (HCP

# Infection prevention and control program.
A multidisciplinary program that includes a group of activities to ensure that recommended practices for the prevention of healthcareassociated infections are implemented and followed by healthcare personnel, making the healthcare setting safe from infection for patients and healthcare personnel. The Joint Commission on Accreditation of Healthcare Organizations (JCAHO) requires the following five components of an infection prevention and control program for accreditation: 1)
surveillance: monitoring patients and healthcare personnel for acquisition of infection and/or colonization; 2) investigation: identification and analysis of infection problems or undesirable trends; 3) prevention: implementation of measures to prevent transmission of infectious agents and to reduce risks for device-and procedure-related infections; 4) control:
evaluation and management of outbreaks; and 5) reporting: provision of information to external agencies as required by state and federal law and regulation (www.jcaho.org). The infection prevention and control program staff has the ultimate authority to determine infection control policies for a healthcare organization with the approval of the organization's governing body.

# Long-term care facilities (LTCFs).An array of residential and outpatient facilities designed
to meet the bio-psychosocial needs of persons with sustained self-care deficits. These include skilled nursing facilities, chronic disease hospitals, nursing homes, foster and group homes, institutions for the developmentally disabled, residential care facilities, assisted living facilities, retirement homes, adult day health care facilities, rehabilitation centers, and long-term psychiatric hospitals.

# Mask.
A term that applies collectively to items used to cover the nose and mouth and includes both procedure masks and surgical masks (www.fda.gov/cdrh/ode/guidance/094.html#4).

# Multidrug-resistant organisms (MDROs).
In general, bacteria (excluding M. tuberculosis)
that are resistant to one or more classes of antimicrobial agents and usually are resistant to all but one or two commercially available antimicrobial agents (e.g., MRSA, VRE, extended spectrum beta-lactamase -producing or intrinsically resistant gram-negative bacilli).

# Nosocomial infection. Derived from two
Greek words "nosos" (disease) and "komeion" (to take care of). Refers to any infection that develops during or as a result of an admission to an acute care facility (hospital) and was not incubating at the time of admission.  Variably described as university hospitals, medical school affiliated hospitals, VA teaching hospitals, and, to a much lesser extent, community teaching hospitals  Includes intensive care units, burn units, dialysis units, hematology/oncology units, neonatal units, neonatal intensive care units, and, in a few instances, individual wards of a hospital  Based on authors' description -if they called their experience an outbreak or not; authors vary in use of term so there is probable overlap between two categories