Methicillin-resistant Staphylococcus Aureus Acquisitions Research Articles

Modeling methicillin-resistant Staphylococcus aureus (MRSA) acquisitions in the intensive care unit with different staffing levels and finite direct-care tasks

Background: Modeling is a cost-effective way to evaluate interventions pertaining to hospital infection acquisitions, such as staffing levels. Increasing the number of nurses in an intensive care unit affects rates of HAI transmission. The way compartmental models are often formulated assumes that there is a never-ending series of tasks for workers to perform. Our previous models used a baseline of 1:3 nurse:patient ratio, and we kept the number of tasks the same across staffing ratios. We wanted to understand how having a finite number of tasks, using this baseline number, across staffing levels affected HAI acquisitions. Methods: We used a stochastic mathematical model of methicillin-resistant Staphylococcus aureus (MRSA) to study the impact of changes in staffing and a finite pool of tasks on hospital-associated acquisitions. For a 15-bed intensive care unit (ICU), we have 1 intensivist, and we set the nurse:patient ratios at 1:1, 1:1.5, 1:2.5, 1:3, 1:5, and 1:7.5, to represent the extreme ends of staffing levels and more moderate values in line with critical care society guidelines. Each model was run 1,000 times. The outcome of each scenario is the median number of hospital-associated MRSA acquisitions in 1 year from those 1,000 runs. Results: Treating the 1:3 nurse:patient ratio as the baseline, with 45 MRSA acquisitions per year, increasing the number of nurses from 5 to 6 (moving to a 1:2.5 nurse:patient ratio) had a relative risk (RR) of 0.77, suggesting that a small change in nurse staffing levels might have an outsized impact on rates. More dramatic changes had correspondingly larger swings in MRSA acquisition rates, with 1:1 nurse:patient ratio scenarios having an RR of 0.17, and at the other extreme, a 1:7.5 nurse:patient ratio having an RR of 4.66. Comparing the infinite to finite models, the ratios with more nurses had lower acquisition rates, with decreases ranging from 20% to 50%. Ratios with fewer nurses in the ICU showed 100%–400% increases in the number of acquisitions. All results were statistically significant. Conclusions: As nurse:patient ratios go up, the burden of direct-care tasks fall on fewer people, which has a direct impact on HAI rates. Our model demonstrates this hypothesis. Therefore, appropriate staffing should be considered in infection control guidelines, and the cost of staffing should be weighed against its impact on infection prevention as well as other areas of patient care. In this study, we considered only the impact from changes in contact patterns emerging from different staffing levels. Further insights may exist when considering other outcomes that also accompany increased staffing.Disclosures: None

Examining the impact of ICU population interaction structure on modeled colonization dynamics of Staphylococcus aureus.

Complex transmission models of healthcare-associated infections provide insight for hospital epidemiology and infection control efforts, but they are difficult to implement and come at high computational costs. Structuring more simplified models to incorporate the heterogeneity of the intensive care unit (ICU) patient-provider interactions, we explore how methicillin-resistant Staphylococcus aureus (MRSA) dynamics and acquisitions may be better represented and approximated. Using a stochastic compartmental model of an 18-bed ICU, we compared the rates of MRSA acquisition across three ICU population interaction structures: a model with nurses and physicians as a single staff type (SST), a model with separate staff types for nurses and physicians (Nurse-MD model), and a Metapopulation model where each nurse was assigned a group of patients. The proportion of time spent with the assigned patient group (γ) within the Metapopulation model was also varied. The SST, Nurse-MD, and Metapopulation models had a mean of 40.6, 32.2 and 19.6 annual MRSA acquisitions respectively. All models were sensitive to the same parameters in the same direction, although the Metapopulation model was less sensitive. The number of acquisitions varied non-linearly by values of γ, with values below 0.40 resembling the Nurse-MD model, while values above that converged toward the Metapopulation structure. Inclusion of complex population interactions within a modeled hospital ICU has considerable impact on model results, with the SST model having more than double the acquisition rate of the more structured metapopulation model. While the direction of parameter sensitivity remained the same, the magnitude of these differences varied, producing different colonization rates across relatively similar populations. The non-linearity of the model's response to differing values of a parameter gamma (γ) suggests simple model approximations are appropriate in only a narrow space of relatively dispersed nursing assignments. Simplifying assumptions around how a hospital population is modeled, especially assuming random mixing, may overestimate infection rates and the impact of interventions. In many, if not most, cases more complex models that represent population mixing with higher granularity are justified.

Assessing the Potential Impact of a Long-Acting Skin Disinfectant in the Prevention of MRSA

Background: Healthcare-associated transmission of methicillin-resistant Staphylococcus aureus (MRSA) remains a persistent problem despite advances in prevention. The use of chlorhexidine gluconate (CHG) as a means of decolonizing patients, either through targeted decolonization or daily bathing, is a frequently used measure to supplement other MRSA reduction interventions. However, there is room for new and innovative decolonizing agents. We explored the potential utility of a long-acting CHG-like disinfectant with a persistent protective effect as well as an immediate decolonizing action in the prevention of MRSA acquisition as well as the subsequent development of clinical illness and MRSA-related mortality. Methods: We modeled MRSA transmission throughout an 18-bed intensive care unit, based on previously published models. A baseline model with no daily decolonizing protocol was used as a baseline and was compared to a scenario assuming that patients were bathed with CHG, which decolonizes them but provides no ongoing protection, as well as a scenario involving a hypothetical treatment that both decolonizes and provides ongoing protection from subsequent colonization. We varied the duration and efficacy of this protection to fully explore the potential utility of such a treatment. Results: The results of the simulations are shown in Fig. 1, where duration and efficacy of protection varied. The number of MRSA acquisitions from each combination is depicted as a single point, with blue points indicating correspondingly fewer MRSA acquisitions. Overall, improved efficacy of the hypothetical disinfectant resulted in immediate improvements in MRSA acquisition rates when compared to the baseline. To see major improvements in the MRSA acquisition rate due to the duration of infection, that duration must be well above 10 hours in many scenarios. There is also little evidence of synergy between the two. Conclusions: Based on recent results suggesting CHG has a relatively modest per-use efficacy (<.20), there is room for improvement in the formulation and administration of decolonizing agents. Although there has been considerable excitement about the possibility of long-acting agents that not only decolonize but provide long-acting protection against colonization, these results suggest that such protection would only result in markedly decreased acquisition rates only if that duration of protection was extremely long, or if the agent itself was also considerably more efficacious than CHG. These results may be used to help consider the necessary study size for clinical studies of these agents in the future, or to set research priorities and properly calibrate expectations.Funding: NoneDisclosures: None

Genomic Surveillance of Methicillin-resistant Staphylococcus aureus: A Mathematical Early Modeling Study of Cost-effectiveness.

BackgroundGenomic surveillance of methicillin-resistant Staphylococcus aureus (MRSA) identifies unsuspected transmission events and outbreaks. Used proactively, this could direct early and highly targeted infection control interventions to prevent ongoing spread. Here, we evaluated the cost-effectiveness of this intervention in a model that compared whole-genome sequencing plus current practice versus current practice alone.MethodsA UK cost-effectiveness study was conducted using an early model built from the perspective of the National Health Service and personal social services. The effectiveness of sequencing was based on the relative reduction in total MRSA acquisitions in a cohort of hospitalized patients in the year following their index admissions. A sensitivity analysis was used to illustrate and assess the level of confidence associated with the conclusions of our economic evaluation.ResultsA cohort of 65 000 patients were run through the model. Assuming that sequencing would result in a 90% reduction in MRSA acquisition, 290 new MRSA cases were avoided. This gave an absolute reduction of 28.8% and avoidance of 2 MRSA-related deaths. Base case results indicated that the use of routine, proactive MRSA sequencing would be associated with estimated cost savings of over £728 290 per annual hospitalized cohort. The impact in total quality-adjusted life years (QALYs) was relatively modest, with sequencing leading to an additional 14.28 QALYs gained. Results were most sensitive to changes in the probability of a MRSA-negative patient acquiring MRSA during their hospital admission.ConclusionsWe showed that proactive genomic surveillance of MRSA is likely to be cost-effective. Further evaluation is required in the context of a prospective study.

Outbreak of clonal complex 22 Panton-Valentine leucocidin-positive methicillin-resistant Staphylococcus aureus.

We describe the investigation and control of a nosocomial outbreak of Sequence Type (ST) 22 MRSA containing the Panton-Valentine leucocidin (PVL) toxin in an acute multispecialty surgical ward at University Hospital Birmingham NHS Foundation Trust. A patient was classed as acquiring methicillin-resistant Staphylococcus aureus (MRSA) if they had a negative admission screen and then had MRSA isolated from a subsequent screen or clinical specimen. Spa typing and pulsed field gel electrophoresis (PFGE) was undertaken to confirm MRSA acquisitions. The Infection Prevention and Control Team were alerted to the possibility of an outbreak when two patients acquired MRSA while being on the same ward. In total, five patients were involved in the outbreak where four patients acquired the PVL-MRSA clone from an index patient due to inadequate infection control practice. Two patients who acquired the strain developed a bloodstream infection. Infection control measures included decolonisation of affected patients, screening of all patients on the ward, environmental sampling and enhanced cleaning. Our study highlights the potential risk of spread and pathogenicity of this clone in the healthcare setting. Spa typing and PFGE assisted with confirmation of the outbreak and implementation of infection control measures. In outbreaks, microbiological typing should be undertaken as a matter of course as without specialist typing identification of the described outbreak would have been delayed.

The Effect of Universal Decolonization With Screening in Critical Care to Reduce MRSA Across an Entire Hospital.

OBJECTIVE To describe the effect of universal methicillin-resistant Staphylococcus aureus (MRSA) decolonization therapy in a large intensive care unit (ICU) on the rates of MRSA cases and acquisitions in a UK hospital. DESIGN Descriptive study. SETTING University Hospitals Birmingham (UHB) NHS Foundation Trust is a tertiary referral teaching hospital in Birmingham, United Kingdom, that provides clinical services to nearly 1 million patients every year. METHODS A break-point time series analysis and kernel regression models were used to detect significant changes in the cumulative monthly numbers of MRSA bacteremia cases and acquisitions from April 2013 to August 2016 across the UHB system. RESULTS Prior to 2014, all ICU patients at UHB received universal MRSA decolonization therapy. In August 2014, UHB discontinued the use of universal decolonization due to published reports in the United Kingdom detailing the limited usefulness and cost-effectiveness of such an intervention. Break-point time series analysis of MRSA acquisition and bacteremia data indicated that break points were associated with the discontinuation and subsequent reintroduction of universal decolonization. Kernel regression models indicated a significant increase (P<.001) in MRSA acquisitions and bacteremia cases across UHB during the period without universal decolonization. CONCLUSION We suggest that routine decolonization for MRSA in a large ICU setting is an effective strategy to reduce the spread and incidence of MRSA across the whole hospital. Infect Control Hosp Epidemiol 2017;38:430-435.

Intra-Facility Acquisition of Methicillin-Resistant Staphylococcus aureus (MRSA) in Southern Wisconsin Skilled Nursing Facilities

BackgroundStudies have shown that skilled nursing facilities (SNFs) are reservoirs for methicillin-resistant Staphylococcus aureus (MRSA). The extent to which resident-to-resident transmission accounts for the high burden of MRSA in these facilities remains poorly understood. The objective of this study was to estimate the frequency of intra-facility MRSA acquisition in a sample of SNFs participating in a longitduinal study in Wisconsin.MethodsMRSA colonization among a cohort of 449 subjects residing in six SNFs in Southern Wisconsin was measured using serial, multi-anatomical surveillance culturing. Phenotypic acquisitions events (i.e., MRSA [-] to MRSA[+]) were identified and further characterized both temporally (calendar date) and genetically (pulse-field gel electrophoresis). An intra-facility acquisition event was defined as incident recovery of an MRSA isolate that was genetically identical to at least one other strain previously recovered in a study facility. A Marascuilo procedure for comparing multiple proportions was employed to determine whether the proportion of intra-facility MRSA acquisitions differed across study facilities. Linear regression was employed to assess if certain facility-level characteristics were associated with rates of intra-facility MRSA acquisition.Results129 acquisition events were identified that met our criteria, of which 74 were determined to be intra-facility (57.4%) [95% CI: 45.5–67.6%]. Statistically significant differences were found between the intra-facility acquisition proportion of multiple SNFs. A facility’s baseline MRSA prevalence was significantly associated with its intra-facility MRSA acquisition rate (R2 = 0.784, P-value = 0.012).ConclusionIntra-facility acquisition represents a large proportion of the burden of MRSA observed in SNFs. The rate of intra-facility acquisition is variable between facilities but may, in part, be explained by the prevalent burden of MRSA in the facility (i.e., MRSA colonization pressure to characteristics of the facility). Whether other facility characteristics, including infection prevention practices are contributing to these transmission dynamics requires further study.Disclosures All authors: No reported disclosures.

Genomic Epidemiology of Methicillin-Resistant Staphylococcus aureus in a Neonatal Intensive Care Unit.

Despite infection prevention efforts, neonatal intensive care unit (NICU) patients remain at risk of Methicillin-resistant Staphylococcus aureus (MRSA) infection. Modes of transmission for healthcare-associated (HA) and community-associated (CA) MRSA remain poorly understood and may vary by genotype, hindering the development of effective prevention and control strategies. From 2008–2010, all patients admitted to a level III NICU were screened for MRSA colonization, and all available isolates were spa-typed. Spa-type t008, the most prevalent CA- genotype in the United States, spa-type t045, a HA- related genotype, and a convenience sample of strains isolated from 2003–2011, underwent whole-genome sequencing and phylodynamic analysis. Patient risk factors were compared between colonized and noncolonized infants, and virulence and resistance genes compared between spa-type t008 and non-t008 strains. Epidemiological and genomic data were used to estimate MRSA importations and acquisitions through transmission reconstruction. MRSA colonization was identified in 9.1% (177/1940) of hospitalized infants and associated with low gestational age and birth weight. Among colonized infants, low gestational age was more common among those colonized with t008 strains. Our data suggest that approximately 70% of colonizations were the result of transmission events within the NICU, with the remainder likely to reflect importations of “outside” strains. While risk of transmission within the NICU was not affected by spa-type, patterns of acquisition and importation differed between t008 and t045 strains. Phylodynamic analysis showed the effective population size of spa-type t008 has been exponentially increasing in both community and hospital, with spa-type t008 strains possessed virulence genes not found among t045 strains; t045 strains, in contrast, appeared to be of more recent origin, with a possible hospital source. Our data highlight the importance of both intra-NICU transmission and recurrent introductions in maintenance of MRSA colonization within the NICU environment, as well as spa-type-specific differences in epidemiology.

Antiseptic Body Washes for Reducing the Transmission of Methicillin-Resistant Staphylococcus aureus: A Cluster Crossover Study.

Background. Limiting the spread of methicillin-resistant Staphylococcus aureus (MRSA) within healthcare facilities where the organism is highly endemic is a challenge. The use of topical antiseptic agents may help interrupt the transmission of MRSA and reduce the risk of clinical infection. Octenidine dihydrochloride is a topical antiseptic that exhibits in vitro efficacy against a wide variety of bacteria, including S aureus. Methods. We conducted a prospective cluster crossover study to compare the use of daily octenidine body washes with soap and water in patients identified by active surveillance cultures to be MRSA-colonized, to prevent the acquisition of MRSA in patients with negative screening swabs. Five adult medical and surgical wards and 2 intensive care units were selected. The study involved an initial 6-month phase using octenidine or soap washes followed by a crossover in each ward to the alternative product. The primary and secondary outcomes were the rates of new MRSA acquisitions and MRSA clinical infections, respectively. Results. A total of 10 936 patients admitted for ≥48 hours was included in the analysis. There was a small reduction in MRSA acquisition in the intervention group compared with controls (3.0% vs 3.3%), but this reduction was not significant (odds ratio, 0.89; 95% confidence interval, .72-1.11; P = .31). There were also no significant differences in clinical MRSA infection or incidence of MRSA bacteremia. Conclusions. This study suggests that the targeted use of routine antiseptic washes may not in itself be adequate to reduce the transmission of MRSA in an endemic hospital setting.

Methicillin-resistant Staphylococcus aureus: site of acquisition and strain variation in high-risk nursing home residents with indwelling devices.

Characterize the clinical and molecular epidemiology of new methicillin-resistant Staphylococcus aureus (MRSA) acquisitions at nasal and extranasal sites among high-risk nursing home (NH) residents. Multicenter prospective observational study. Six NHs in southeast Michigan. A total of 120 NH residents with an indwelling device (feeding tube and/or urinary catheter). Active surveillance cultures from the nares, oropharynx, groin, perianal area, wounds (if present), and device insertion site(s) were collected upon enrollment, at day 14, and monthly thereafter. Pulsed-field gel electrophoresis and polymerase chain reaction for SCCmec, agr, and Panton-Valentine leukocidin were performed. Of 120 participants observed for 16,290 device-days, 50 acquired MRSA (78% transiently, 22% persistently). New MRSA acquisitions were common in extranasal sites, particularly at device insertion, groin, and perianal areas (27%, 23%, and 17.6% of all acquisitions, respectively). Screening extranasal sites greatly increases the detection of MRSA colonization (100% of persistent carriers and 97.4% of transient carriers detected with nares, groin, perianal, and device site sampling vs 54.5% and 25.6%, respectively, for nares samples alone). Colonization at suprapubic urinary catheter sites generally persisted. Healthcare-associated MRSA (USA100 and USA100 variants) were the dominant strains (79.3% of all new acquisition isolates). Strain diversity was more common in transient carriers, including acquisition of USA500 and USA300 strains. Indwelling device insertion sites as well as the groin and perianal area are important sites of new MRSA acquisitions in NH residents and play a role in the persistency of MRSA carriage. Clonal types differ among persistent and transient colonizers.

Prior room occupancy increases risk of methicillin-resistant Staphylococcus aureus acquisition

Abstract Background In Australia, little is known about the risk of acquiring methicillin-resistant Staphylococcus aureus (MRSA) from prior room occupants. The aims of the study are to understand the risk of MRSA acquisition from prior room occupants and to further extend the existing knowledge-base on the role of discharge cleaning in hospitals. Methods A non-concurrent cohort study was undertaken in five wards at a 250-bed general hospital in Tasmania, Australia. All admitted patients were screened for MRSA. Weekly screenings for all patients who remained in hospital were undertaken. New MRSA acquisitions were identified. The exposed group were patients whose immediate prior room occupant had MRSA, while the unexposed prior room occupant did not have MRSA. Results 6228 patients were at risk of acquiring MRSA, with 237 new MRSA acquisitions equating to an acquisition rate of 3.8% for each at-risk patient admission. The unadjusted odds ratio for acquiring MRSA when the prior room occupant had MRSA was 2.9 (95% CI 2.2–3.9). Using logistic regression, exposure to a prior occupant harbouring MRSA remained a significant predictor of subsequent acquisition, after controlling for variables, OR 2.7 (95% CI 2.0–3.6). Conclusion Admission to a room previously occupied by a person with MRSA increased the odds of acquisition forthe subsequentpatient, independent of other risk factors. It demonstrates the necessity of having effective discharge cleaning practices in place. We believe increased attention to discharge room cleaning in hospitals is required and the reconsideration of additional recommendations for discharge cleaning.

Active Surveillance and Decolonization Without Isolation Is Effective in Preventing Methicillin-Resistant Staphylococcus aureus Transmission in the Psychiatry Units.

Background Control of methicillin-resistant Staphylococcus aureus (MRSA) is difficult in select populations. We used molecular typing to study the effect of universal surveillance and decolonization of carriers, without isolation, on MRSA transmission in a specialized unit.Methods Patients admitted to the unit were screened for nasal MRSA at admission and discharge. Those who acquired MRSA during their stay were identified and linked to carriers with shared time in unit. Molecular typing of isolates was performed to identify transmission.Results Of 3285 admissions, 82% were tested for MRSA nasal carriage; the discharge screening compliance was 64.7%. Admission prevalence was 2.3% among patients screened, and 7 (0.42%) acquired nasal MRSA during their stay. All patients who acquired MRSA shared time in the unit with a colonized patient. There were 3.9 MRSA acquisitions per 1000 at-risk days. Isolates from 5 patients that acquired MRSA during their stay as well as their potential donors (11 donor: recipient patient pairs) were available for typing. Pulsed-field gel electrophoresis matched 1 acquisition isolate to a colonized patient isolate. There were no MRSA infections during the study period.Conclusions Despite less than perfect nasal screening compliance and exemption from traditional isolation precautions, acquisition of MRSA was 0.42% in this patient population over a course of 4.75 years, including a single case of acquisition, genetically similar to a known potential donor source. Screening for MRSA colonization and decolonizing of carriers was sufficient in reducing transmission in this vulnerable population.

Methicillin-Resistant Staphylococcus aureus Colonization: A Three-Year Prospective Study in a Neonatal Intensive Care Unit in Italy

BackgroundMethicillin resistant Staphylococcus aureus (MRSA) is a major etiological agent of infection in neonatal intensive care units (NICUs). Routes of entry of this organism can be different and the transmission pathway complex. Colonized neonates are the main endogenous reservoir.Methods and ResultsWe conducted a prospective three-year study on MRSA colonization recruiting 722 neonates admitted between 2009 and 2012. Nasal swabs were cultured weekly and MRSA isolates were submitted to molecular typing. The annual incidence density of acquisition of MRSA ranged from a maximum of 20.2 cases for 1000 patient-days during the first year to a minimum of 8.8 cases in the second one to raise again up to 13.1 cases during the third year. The mean weekly colonization pressure fluctuated from 19.1% in the first year to 13.4% in the second year and 16.8% in the third year. It significantly correlated with the number of MRSA acquisitions in the following week. Overall, 187 (25.9%) subjects tested positive for MRSA. A non multiresistant, tst positive, ST22-MRSA-IVa spa t223 strain proved to be endemic in the NICU, being identified in 166 (88.8%) out of 187 colonized neonates. Sporadic or epidemic occurrence of other strains was detected.ConclusionsAn MRSA strain belonging to the tst1 positive, UK-EMRSA-15/ “Middle Eastern Variant” appeared to be endemic in the NICU under investigation. During the three-year period, substantial changes occurred in case-mix of patients moving towards a higher susceptibility to MRSA colonization. The infection control procedures were able to decrease the colonization rate from more than 40% to approximately 10%, except for an outbreak due to a CA-MRSA strain, ST1-MRSA-IVa, and a transient increase in the colonization prevalence rate coincident with a period of substantial overcrowding of the ward. Active surveillance and molecular typing contributed to obtain a reliable picture of the MRSA dissemination in NICU.

Improving hand hygiene compliance in health care workers: Strategies and impact on patient outcomes

We described a systematic process for improving hand hygiene (HH) compliance in health care providers and assessed the impact of HH on patient outcomes. This retrospective cohort study was conducted between July 2008 and September 2011 in a children's hospital. We employed failure mode effectiveness analysis to identify barriers for complying with HH requirements and instituted improvement measures. We conducted a subanalysis using methicillin-resistant Staphylococcus aureus (MRSA) acquisition data and HH compliance data collected in the neonatal intensive care unit (NICU) to demonstrate the impact of HH on patient outcomes. The overall HH compliance rate increased from 50.3% preintervention (July 2008-September 2008) to 84.0% postintervention (January 2009-September 2011) (relative risk [RR], 1.7; 95% confidence interval [CI]: 1.6-1.9). Compliance among physicians and nurses increased from 48.6% to 87.0% (RR, 1.4; 95% CI: 1.3-1.6) and from 46.5% to 77.9% (RR, 1.3; 95% CI: 1.2-1.4), respectively. Sustaining HH at 80% or higher was associated with a 48% further reduction of MRSA acquisition (incident rate ratio, -0.52; 95% CI: -0.31 to -0.90) in a unit that had comprehensive MRSA prevention measures. This reduction represents the prevention of 1.3 MRSA acquisitions per month, resulting in a saving of 11.6 NICU-days and $66,397 hospital charges. This study demonstrated the utility of failure mode effectiveness analysis to improve staff HH and suggested HH as a potential cost-effective means for preventing MRSA in hospitals.

Decolonization of patients and health care workers to control nosocomial spread of methicillin-resistant Staphylococcus aureus:a simulation study

BackgroundControl of methicillin-resistant Staphylococcus aureus (MRSA) transmission has been unsuccessful in many hospitals. Recommended control measures include isolation of colonized patients, rather than decolonization of carriage among patients and/or health care workers. Yet, the potential effects of such measures are poorly understood.MethodsWe use a stochastic simulation model in which health care workers can transmit MRSA through short-lived hand contamination, or through persistent colonization. Hand hygiene interrupts the first mode, decolonization strategies the latter. We quantified the effectiveness of decolonization of patients and health care workers, relative to patient isolation in settings where MRSA carriage is endemic (rather than sporadic outbreaks in non-endemic settings caused by health care workers).ResultsPatient decolonization is the most effective intervention and outperforms patient isolation, even with low decolonization efficacy and when decolonization is not achieved immediately. The potential role of persistently colonized health care workers in MRSA transmission depends on the proportion of persistently colonized health care workers and the likelihood per colonized health care worker to transmit. As stand-alone intervention, universal screening and decolonization of persistently colonized health care workers is generally the least effective intervention, especially in high endemicity settings. When added to patient isolation, such a strategy would have maximum benefits if few health care workers cause a large proportion of the acquisitions.ConclusionsIn high-endemicity settings regular screening of health care workers followed by decolonization of MRSA-carriers is unlikely to reduce nosocomial spread of MRSA unless there are few persistently colonized health care workers who are responsible for a large fraction of the MRSA acquisitions by patients. In contrast, decolonization of patients can be very effective.

Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Carriage in Residents of Veterans Affairs Long-Term Care Facilities: Role of Antimicrobial Exposure and MRSA Acquisition

To identify risk factors associated with methicillin-resistant Staphylococcus aureus (MRSA) acquisition in long-term care facility (LTCF) residents. Multicenter, prospective cohort followed over 6 months. Three Veterans Affairs (VA) LTCFs. All current and new residents except those with short stay (<2 weeks). MRSA carriage was assessed by serial nares cultures and classified into 3 groups: persistent (all cultures positive), intermittent (at least 1 but not all cultures positive), and noncarrier (no cultures positive). MRSA acquisition was defined by an initial negative culture followed by more than 2 positive cultures with no subsequent negative cultures. Epidemiologic data were collected to identify risk factors, and MRSA isolates were typed by pulsed-field gel electrophoresis (PFGE). Among 412 residents at 3 LTCFs, overall MRSA prevalence was 58%, with similar distributions of carriage at all 3 facilities: 20% persistent, 39% intermittent, 41% noncarriers. Of 254 residents with an initial negative swab, 25 (10%) acquired MRSA over the 6 months; rates were similar at all 3 LTCFs, with no clusters evident. Multivariable analysis demonstrated that receipt of systemic antimicrobials during the study was the only significant risk factor for MRSA acquisition (odds ratio, 7.8 [95% confidence interval, 2.1-28.6]; P = .002). MRSA strains from acquisitions were related by PFGE to those from a roommate in 9/25 (36%) cases; 6 of these 9 roommate sources were persistent carriers. MRSA colonization prevalence was high at 3 separate VA LTCFs. MRSA acquisition was strongly associated with antimicrobial exposure. Roommate sources were often persistent carriers, but transmission from roommates accounted for only approximately one-third of MRSA acquisitions.

Efficacy and Limitation of a Chlorhexidine‐Based Decolonization Strategy in Preventing Transmission of Methicillin‐ResistantStaphylococcus aureusin an Intensive Care Unit

Surface-active antiseptics, such as chlorhexidine, are increasingly being used as part of intervention programs to prevent methicillin-resistant Staphylococcus aureus (MRSA) transmission, despite limited evidence and potential for resistance. We report on the effect of an antiseptic protocol on acquisition of both endemic MRSA and an outbreak strain of MRSA sequence type 239 (designated TW). Interrupted time-series data on MRSA acquisitions in two 15-bed intensive care units were analyzed using segmented regression models to estimate the effects of sequential introduction of an educational campaign, cohorting, and a chlorhexidine-based antiseptic protocol on transmission of TW and non-TW MRSA strains. Representative TW and non-TW MRSA strains were assessed for carriage of qacA/B genes and antiseptic susceptibility. The antiseptic protocol was associated with a highly significant, immediate 70% reduction in acquisition of non-TW MRSA strains (estimated model-averaged incidence rate ratio, 0.3; 95% confidence interval, 0.19-0.47) and an increase in acquisition of TW MRSA strains (estimated model-averaged incidence rate ratio, 3.85; 95% confidence interval, 0.80-18.59). There was only weak evidence of an effect of other interventions on MRSA transmission. All TW MRSA strains (21 of 21 isolates) and <5% (1 of 21 isolates) of non-TW MRSA strains tested carried the chlorhexidine resistance loci qacA/B. In vitro chlorhexidine minimum bactericidal concentrations of TW strains were 3-fold higher than those of non-TW MRSA strains, and in vivo, only patients with non-TW MRSA demonstrated a reduction in the number of colonization sites in response to chlorhexidine treatment. A chlorhexidine-based surface antiseptic protocol can interrupt transmission of MRSA in the intensive care unit, but strains carrying qacA/B genes may be unaffected or potentially spread more rapidly.