Water Cultures Are More Sensitive Than Swab Cultures for the Detection of Environmental Legionella.

Water cultures were significantly more sensitive than concurrently collected swab cultures (n=2,147 each) in detecting Legionella pneumophila within a Veterans Affairs healthcare system. Sensitivity for water versus swab cultures was 90% versus 30% overall, 83% versus 48% during a nosocomial Legionnaires' disease outbreak, and 93% versus 22% post outbreak. Infect Control Hosp Epidemiol 2018;39:108-110.

Improving the Diagnosis of Legionella Pneumonia within a Healthcare System through a Systematic Consultation and Testing Program.

RATIONALE: Legionella testing is not recommended for all patients with pneumonia, but rather for particular patient subgroups. As a result, the overall incidence of Legionella pneumonia may be underestimated. OBJECTIVES: To determine the incidence of Legionella pneumonia in a veteran population in an endemic area after introduction of a systematic infectious diseases consultation and testing program. METHODS: In response to a 2011-2012 outbreak, the VA Pittsburgh Healthcare System mandated infectious diseases consultations and testing for Legionella by urine antigen and sputum culture in all patients with pneumonia. MEASUREMENTS AND MAIN RESULTS: Between January 2013 and December 2015, 1,579 cases of pneumonia were identified. The incidence of pneumonia was 788/100,000 veterans per year, including 352/100,000 veterans per year and 436/100,000 veterans per year with community-associated pneumonia (CAP) and health care-associated pneumonia, respectively. Ninety-eight percent of patients with suspected pneumonia were tested for Legionella by at least one method. Legionella accounted for 1% of pneumonia cases (n = 16), including 1.7% (12/706) and 0.6% (4/873) of CAP and health care-associated pneumonia, respectively. The yearly incidences of Legionella pneumonia and Legionella CAP were 7.99 and 5.99/100,000 veterans, respectively. The sensitivities of urine antigen and sputum culture were 81% and 60%, respectively; the specificity of urine antigen was >99.97%. Urine antigen testing and Legionella cultures increased by 65% and 330%, respectively, after introduction of our program. CONCLUSIONS: Systematic testing of veterans in an endemic area revealed a higher incidence of Legionella pneumonia and CAP than previously reported. Widespread urine antigen testing was not limited by false positivity.

The importance of clinical surveillance in detecting legionnaires' disease outbreaks: a large outbreak in a hospital with a Legionella disinfection system-Pennsylvania, 2011-2012.

BACKGROUND: Healthcare-associated Legionnaires' disease (LD) is a preventable pneumonia with a 30% case fatality rate. The Centers for Disease Control and Prevention guidelines recommend a high index of suspicion for the diagnosis of healthcare-associated LD. We characterized an outbreak and evaluated contributing factors in a hospital using copper-silver ionization for prevention of Legionella growth in water. METHODS: Through medical records review at a large, urban tertiary care hospital in November 2012, we identified patients diagnosed with LD during 2011-2012. Laboratory-confirmed cases were categorized as definite, probable, and not healthcare associated based on time spent in the hospital during the incubation period. We performed an environmental assessment of the hospital, including collection of samples for Legionella culture. Clinical and environmental isolates were compared by genotyping. Copper and silver ion concentrations were measured in 11 water samples. RESULTS: We identified 5 definite and 17 probable healthcare-associated LD cases; 6 case patients died. Of 25 locations (mostly potable water) where environmental samples were obtained for Legionella-specific culture, all but 2 showed Legionella growth; 11 isolates were identical to 3 clinical isolates by sequence-based typing. Mean copper and silver concentrations were at or above the manufacturer's recommended target for Legionella control. Despite this, all samples where copper and silver concentrations were tested showed Legionella growth. CONCLUSIONS: This outbreak was linked to the hospital's potable water system and highlights the importance of maintaining a high index of suspicion for healthcare-associated LD, even in the setting of a long-term disinfection program.

An economic model: value of antimicrobial-coated sutures to society, hospitals, and third-party payers in preventing abdominal surgical site infections.

BACKGROUND: While the persistence of high surgical site infection (SSI) rates has prompted the advent of more expensive sutures that are coated with antimicrobial agents to prevent SSIs, the economic value of such sutures has yet to be determined. METHODS: Using TreeAge Pro, we developed a decision analytic model to determine the cost-effectiveness of using antimicrobial sutures in abdominal incisions from the hospital, third-party payer, and societal perspectives. Sensitivity analyses systematically varied the risk of developing an SSI (range, 5%-20%), the cost of triclosan-coated sutures (range, $5-$25/inch), and triclosan-coated suture efficacy in preventing infection (range, 5%-50%) to highlight the range of costs associated with using such sutures. RESULTS: Triclosan-coated sutures saved $4,109-$13,975 (hospital perspective), $4,133-$14,297 (third-party payer perspective), and $40,127-$53,244 (societal perspective) per SSI prevented, when a surgery had a 15% SSI risk, depending on their efficacy. If the SSI risk was no more than 5% and the efficacy in preventing SSIs was no more than 10%, triclosan-coated sutures resulted in extra expenditure for hospitals and third-party payers (resulting in extra costs of $1,626 and $1,071 per SSI prevented for hospitals and third-party payers, respectively; SSI risk, 5%; efficacy, 10%). CONCLUSIONS: Our results suggest that switching to triclosan-coated sutures from the uncoated sutures can both prevent SSIs and save substantial costs for hospitals, third-party payers, and society, as long as efficacy in preventing SSIs is at least 10% and SSI risk is at least 10%.

Risk factors for acquisition of multidrug-resistant Acinetobacter baumannii among cancer patients.

BACKGROUND: Data regarding multidrug-resistant (MDR) Acinetobacter baumannii infections among cancer patients are limited. METHODS: We conducted a case-control study to investigate the risk factors for acquisition of MDR A baumannii and the outcomes among cancer patients. Cases were inpatients with malignancy who had MDR A baumannii from any cultures between 2008 and 2011. Controls were inpatients with malignancy but no MDR A baumannii. RESULTS: A total of 31 case patients were matched with 62 control patients. Hematologic malignancy (P = .036), need for dialysis (P = .01), admission for other reasons except elective surgery (P = .03), transfer from other health care facilities (P = .02), prolonged intensive care unit stay (P = .004), mechanical ventilation (P < .001), pressor use (P = .001), tube feeding (P < .001), transfusion (P = .009), and prior antimicrobial use (P < .001) were identified as significant risk factors in univariate analysis. Need for dialysis (odds ratio [OR], 18.23; P = .04) and prolonged intensive care unit stay (OR, 19.28; P = .01) remained significant in multivariate analysis. Lengths of stay were 28 days for the case patients and 10 days for the control patients (P = .001). The 90-day mortality rates were 41.9% and 29.0%, respectively (P = .20). CONCLUSIONS: Acquisition of MDR A baumannii among cancer patients appears to be associated with general nosocomial infection risk factors rather than underlying malignancies.

Infections in psychiatric facilities, with an emphasis on outbreaks.

Outbreaks of infectious diseases in psychiatric units are very different from those in intensive care units or acute medical-surgical units. Outbreaks in psychiatric units are most often caused by agents circulating in the community. Infection control in psychiatric units also faces unique challenges due to the characteristics of the patients and facilities.

Identifying the risk factors for hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) infection among patients colonized with MRSA on admission.

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen in hospital-acquired infections. MRSA-colonized inpatients who may benefit from undergoing decolonization have not been identified. OBJECTIVE: To identify risk factors for MRSA infection among patients who are colonized with MRSA at hospital admission. DESIGN: A case-control study. SETTING: A 146-bed Veterans Affairs hospital. PARTICIPANTS: Case patients were those patients admitted from January 2003 to August 2011 who were found to be colonized with MRSA on admission and then developed MRSA infection. Control subjects were those patients admitted during the same period who were found to be colonized with MRSA on admission but who did not develop MRSA infection. METHODS: A retrospective review. RESULTS: A total of 75 case patients and 150 control subjects were identified. A stay in the intensive care unit (ICU) was the significant risk factor in univariate analysis (P<.001). Prior history of MRSA (P=.03), transfer from a nursing home (P=.002), experiencing respiratory failure (P<.001), and receipt of transfusion (P=.001) remained significant variables in multivariate analysis. Prior history of MRSA colonization or infection (P=.02]), difficulty swallowing (P=.04), presence of an open wound (P=.02), and placement of a central line (P=.02) were identified as risk factors for developing MRSA infection for patients in the ICU. Duration of hospitalization, readmission rate, and mortality rate were significantly higher in case patients than in control subjects (P < .001, .001, and <.001, respectively). CONCLUSIONS: MRSA-colonized patients admitted to the ICU or admitted from nursing homes have a high risk of developing MRSA infection. These patients may benefit from undergoing decolonization.

Identifying the incidence of and risk factors for reamputation among patients who underwent foot amputation.

BACKGROUND: Many patients who have lower-extremity amputations secondary to peripheral vascular disease or diabetes require reamputation eventually. This study was designed to identify the incidence of and risk factors for ipsilateral reamputation after forefoot amputation, to evaluate whether postoperative infection increases the risk of reamputation, and to evaluate whether the risk of reamputation was reduced by the duration of antimicrobial therapy after amputation. METHODS: A retrospective analysis of patients who underwent foot amputation for nontraumatic reason from January 2002 to December 2004 at the Veterans Affairs Pittsburgh Healthcare System was performed. RESULTS: Among 116 patients, 57 (49.1%) had ipsilateral reamputation within 3 years after their first surgeries; 78.9% received reamputation in the first 6 months; 53 (45.7%) died within 3 years; and 16 (13.8%) developed postoperative infections. Upper level of amputation, long duration of hospitalization, insulin-dependent diabetes, and gangrene on physical examination on admission were risk factors for reamputation in univariate analysis. Gangrene (odds ratio: 3.81, 95% confidence interval: 1.60-9.12, P = 0.003) and insulin-dependent diabetes (odds ratio: 2.93, 95% confidence interval: 1.26-6.78, P = 0.012) were risk factors in multivariate analysis. Postoperative infection did not increase the risk of reamputation. Longer than 2-week course of antibiotic use after amputation did not prevent reamputation. CONCLUSIONS: Approximately one-half of patients required ipsilateral reamputation and died in 3 years. Gangrene on admission and history of insulin-dependent diabetes were significant risk factors (P = 0.003, P = 0.028). Long duration of antibiotic use after amputation and postoperative infection did not change the risk of reamputation.

The potential economic value of a Staphylococcus aureus vaccine among hemodialysis patients.

Staphylococcus aureus infections are a substantial problem for hemodialysis patients. Several vaccine candidates are currently under development, with hemodialysis patients being one possible target population. To determine the potential economic value of an S. aureus vaccine among hemodialysis patients, we developed a Markov decision analytic computer simulation model. When S. aureus colonization prevalence was 1%, the incremental cost-effectiveness ratio (ICER) of vaccination was ≤$25,217/quality-adjusted life year (QALY). Vaccination became more cost-effective as colonization prevalence, vaccine efficacy, or vaccine protection duration increased or vaccine cost decreased. Even at 10% colonization prevalence, a 25% efficacious vaccine costing $100 prevented 29 infections, 21 infection-related hospitalizations, and 9 inpatient deaths per 1000 vaccinated HD patients. Our results suggest that an S. aureus vaccine would be cost-effective (i.e., ICERs ≤ $50,000/QALY) among hemodialysis patients over a wide range of S. aureus prevalence, vaccine costs and efficacies, and vaccine protection durations and delineate potential target parameters for such a vaccine.

Clostridium difficile infection in a long-term care facility: hospital-associated illness compared with long-term care-associated illness.

BACKGROUND: Controversy exists over whether Clostridium difficile infection (CDI) commonly occurs in long-term care facility residents who have not been recently transferred from an acute care hospital. OBJECTIVE: To assess the incidence and outcome of CDI in a long-term care facility. METHODS: Retrospective cohort study in a 262-bed long-term care Veterans Affairs facility in Pittsburgh, Pennsylvania, for the period January 2004 through June 2010. CDI was identified by positive stool C. difficile toxin assay and acute diarrhea. Patients were categorized as hospital-associated CDI (HACDI) or long-term care facility-associated CDI (LACDI) and followed for 6 months. RESULTS: The annual rate of CDI varied between 0.11 and 0.23 per 1,000 resident-days for HACDI patients and between 0.04 and 0.28 per 1,000 resident-days for LACDI patients. We identified 162 patients, 96 patients (59.3%) with HACDI and 66 patients (40.7%) with LACDI. Median age was 74 and 77 years, respectively, for HACDI and LACDI (P = .055) patients. There were more patients with at least 1 relapse of CDI during 6 months of follow up in LACDI patients (32/66, 48.5%) than in HACDI patients (28/96, 29.2%; P = .005). Logistic regression showed that ages of at least 75 years (odds ratio [OR], 2.33; 95% confidence interval [CI], 1.07-5.07; P = .005), more than 2 transfers to an acute care hospital (OR, 7.88; 95% CI, 1.88-32.95; P = .005), and LACDI (OR, 3.15; 95% CI, 1.41-7.05; P = .005) were associated with relapse of CDI. CONCLUSIONS: Forty percent of CDI cases were acquired within the long-term care facility, indicating a substantial degree of transmission. Optimal strategies to prevent CDI in the long-term care facility are needed.

Economic value of dispensing home-based preoperative chlorhexidine bathing cloths to prevent surgical site infection.

OBJECTIVE: To estimate the economic value of dispensing preoperative home-based chlorhexidine bathing cloth kits to orthopedic patients to prevent surgical site infection (SSI). METHODS: A stochastic decision-analytic computer simulation model was developed from the hospital's perspective depicting the decision of whether to dispense the kits preoperatively to orthopedic patients. We varied patient age, cloth cost, SSI-attributable excess length of stay, cost per bed-day, patient compliance with the regimen, and cloth antimicrobial efficacy to determine which variables were the most significant drivers of the model's outcomes. RESULTS: When all other variables remained at baseline and cloth efficacy was at least 50%, patient compliance only had to be half of baseline (baseline mean, 15.3%; range, 8.23%-20.0%) for chlorhexidine cloths to remain the dominant strategy (ie, less costly and providing better health outcomes). When cloth efficacy fell to 10%, 1.5 times the baseline bathing compliance also afforded dominance of the preoperative bath. CONCLUSIONS: The results of our study favor the routine distribution of bathing kits. Even with low patient compliance and cloth efficacy values, distribution of bathing kits is an economically beneficial strategy for the prevention of SSI.

Veterans Affairs initiative to prevent methicillin-resistant Staphylococcus aureus infections.

BACKGROUND: Health care-associated infections with methicillin-resistant Staphylococcus aureus (MRSA) have been an increasing concern in Veterans Affairs (VA) hospitals. METHODS: A "MRSA bundle" was implemented in 2007 in acute care VA hospitals nationwide in an effort to decrease health care-associated infections with MRSA. The bundle consisted of universal nasal surveillance for MRSA, contact precautions for patients colonized or infected with MRSA, hand hygiene, and a change in the institutional culture whereby infection control would become the responsibility of everyone who had contact with patients. Each month, personnel at each facility entered into a central database aggregate data on adherence to surveillance practice, the prevalence of MRSA colonization or infection, and health care-associated transmissions of and infections with MRSA. We assessed the effect of the MRSA bundle on health care-associated MRSA infections. RESULTS: From October 2007, when the bundle was fully implemented, through June 2010, there were 1,934,598 admissions to or transfers or discharges from intensive care units (ICUs) and non-ICUs (ICUs, 365,139; non-ICUs, 1,569,459) and 8,318,675 patient-days (ICUs, 1,312,840; and non-ICUs, 7,005,835). During this period, the percentage of patients who were screened at admission increased from 82% to 96%, and the percentage who were screened at transfer or discharge increased from 72% to 93%. The mean (±SD) prevalence of MRSA colonization or infection at the time of hospital admission was 13.6±3.7%. The rates of health care-associated MRSA infections in ICUs had not changed in the 2 years before October 2007 (P=0.50 for trend) but declined with implementation of the bundle, from 1.64 infections per 1000 patient-days in October 2007 to 0.62 per 1000 patient-days in June 2010, a decrease of 62% (P<0.001 for trend). During this same period, the rates of health care-associated MRSA infections in non-ICUs fell from 0.47 per 1000 patient-days to 0.26 per 1000 patient-days, a decrease of 45% (P<0.001 for trend). CONCLUSIONS: A program of universal surveillance, contact precautions, hand hygiene, and institutional culture change was associated with a decrease in health care-associated transmissions of and infections with MRSA in a large health care system.

Sustained reduction in the clinical incidence of methicillin-resistant Staphylococcus aureus colonization or infection associated with a multifaceted infection control intervention.

OBJECTIVE: To assess the impact and sustainability of a multifaceted intervention to prevent methicillin-resistant Staphylococcus aureus (MRSA) transmission implemented in 3 chronologically overlapping phases at 1 hospital. DESIGN: Interrupted time-series analyses. SETTING: A Veterans Affairs hospital in the northeastern United States. PATIENTS AND PARTICIPANTS: Individuals admitted to acute care units from October 1, 1999, through September 30, 2008. To calculate the monthly clinical incidence of MRSA colonization or infection, the number of MRSA-positive cultures obtained from a clinical site more than 48 hours after admission among patients with no MRSA-positive clinical cultures during the previous year was divided by patient-days at risk. Secondary outcomes included clinical incidence of methicillin-sensitive S. aureus colonization or infection and incidence of MRSA bloodstream infections. INTERVENTIONS: The intervention--implemented in a surgical ward beginning October 2001, in a surgical intensive care unit beginning October 2003, and in all acute care units beginning July 2005--included systems and behavior change strategies to increase adherence to infection control precautions (eg, hand hygiene and active surveillance culturing for MRSA). RESULTS: Hospital-wide, the clinical incidence of MRSA colonization or infection decreased after initiation of the intervention in 2001, compared with the period before intervention (P = .002), and decreased by 61% (P < .001) in the 7-year postintervention period. In the postintervention period, the hospital-wide incidence of MRSA bloodstream infection decreased by 50% (P = .02), and the proportion of S. aureus isolates that were methicillin resistant decreased by 30% (P < .001). CONCLUSIONS: Sustained decreases in hospital-wide clinical incidence of MRSA colonization or infection, incidence of MRSA bloodstream infection, and proportion of S. aureus isolates resistant to methicillin followed implementation of a multifaceted prevention program at one Veterans Affairs hospital. Findings suggest that interventions designed to prevent transmission can impact endemic antimicrobial resistance problems.

The economic effect of screening orthopedic surgery patients preoperatively for methicillin-resistant Staphylococcus aureus.

BACKGROUND AND OBJECTIVE: Patients undergoing orthopedic surgery are susceptible to methicillin-resistant Staphylococcus aureus (MRSA) infections, which can result in increased morbidity, hospital lengths of stay, and medical costs. We sought to estimate the economic value of routine preoperative MRSA screening and decolonization of orthopedic surgery patients. METHODS: A stochastic decision-analytic computer simulation model was used to evaluate the economic value of implementing this strategy (compared with no preoperative screening or decolonization) among orthopedic surgery patients from both the third-party payer and hospital perspectives. Sensitivity analyses explored the effects of varying MRSA colonization prevalence, the cost of screening and decolonization, and the probability of decolonization success. RESULTS: Preoperative MRSA screening and decolonization was strongly cost-effective (incremental cost-effectiveness ratio less than $6,000 per quality-adjusted life year) from the third-party payer perspective even when MRSA prevalence was as low as 1%, decolonization success was as low as 25%, and decolonization costs were as high as $300 per patient. In most scenarios this strategy was economically dominant (ie, less costly and more effective than no screening). From the hospital perspective, preoperative MRSA screening and decolonization was the economically dominant strategy for all scenarios explored. CONCLUSIONS: Routine preoperative screening and decolonization of orthopedic surgery patients may under many circumstances save hospitals and third-party payers money while providing health benefits.

Screening cardiac surgery patients for MRSA: an economic computer model.

OBJECTIVE: To estimate the economic value of preoperative methicillin-resistant Staphylococcus aureus (MRSA) screening and decolonization for cardiac surgery patients. STUDY DESIGN: Monte Carlo decision-analytic computer simulation model. METHODS: We developed a computer simulation model representing the decision of whether to perform preoperative MRSA screening and decolonizing those patients with a positive MRSA culture. Sensitivity analyses varied key input parameters including MRSA colonization prevalence, decolonization success rates, the number of surveillance sites, and screening/decolonization costs. Separate analyses estimated the incremental cost-effectiveness ratio (ICER) of the screening and decolonization strategy from the third-party payer and hospital perspectives. RESULTS: Even when MRSA colonization prevalence and decolonization success rate were as low as 1% and 25%, respectively, the ICER of implementing routine surveillance was well under $15,000 per quality-adjusted life-year from both the third-party payer and hospital perspectives. The surveillance strategy was economically dominant (less costly and more effective than no testing) for most scenarios explored. CONCLUSIONS: Our results suggest that routine preoperative MRSA screening of cardiac surgery patients could provide substantial economic value to third-party payers and hospitals over a wide range of MRSA colonization prevalence levels, decolonization success rates, and surveillance costs. Healthcare administrators, infection control specialists, and surgeons can compare their local conditions with our study's benchmarks to make decisions about whether to implement preoperative MRSA testing. Third-party payers may want to consider covering such a strategy.

The potential value of Clostridium difficile vaccine: an economic computer simulation model.

Efforts are currently underway to develop a vaccine against Clostridium difficile infection (CDI). We developed two decision analytic Monte Carlo computer simulation models: (1) an Initial Prevention Model depicting the decision whether to administer C. difficile vaccine to patients at-risk for CDI and (2) a Recurrence Prevention Model depicting the decision whether to administer C. difficile vaccine to prevent CDI recurrence. Our results suggest that a C. difficile vaccine could be cost-effective over a wide range of C. difficile risk, vaccine costs, and vaccine efficacies especially, when being used post-CDI treatment to prevent recurrent disease.

The potential economic value of a Staphylococcus aureus vaccine for neonates.

The continuing morbidity and mortality associated with Staphylococcus aureus (S. aureus) infections, especially methicillin-resistant S. aureus (MRSA) infections, have motivated calls to make S. aureus vaccine development a research priority. We developed a decision analytic computer simulation model to determine the potential economic impact of a S. aureus vaccine for neonates. Our results suggest that a S. aureus vaccine for the neonatal population would be strongly cost-effective (and in many situations dominant) over a wide range of vaccine efficacies (down to 10%) for vaccine costs (or=1%).

Universal methicillin-resistant Staphylococcus aureus (MRSA) surveillance for adults at hospital admission: an economic model and analysis.

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) transmission and infections are a continuing problem in hospitals. Although some have recommended universal surveillance for MRSA at hospital admission to identify and to isolate MRSA-colonized patients, there is a need for formal economic studies to determine the cost-effectiveness of such a strategy. METHODS: We developed a stochastic computer simulation model to determine the potential economic impact of performing MRSA surveillance (ie, single culture of an anterior nares specimen) for all hospital admissions at different MRSA prevalences and basic reproductive rate thresholds from the societal and third party-payor perspectives. Patients with positive surveillance culture results were placed under isolation precautions to prevent transmission by way of respiratory droplets. MRSA-colonized patients who were not isolated could transmit MRSA to other hospital patients. RESULTS: The performance of universal MRSA surveillance was cost-effective (defined as an incremental cost-effectiveness ratio of less than $50,000 per quality-adjusted life-year) when the basic reproductive rate was 0.25 or greater and the prevalence was 1% or greater. In fact, surveillance was the dominant strategy when the basic reproductive rate was 1.5 or greater and the prevalence was 15% or greater, the basic reproductive rate was 2.0 or greater and the prevalence was 10% or greater, and the basic reproductive rate was 2.5 or greater and the prevalence was 5% or greater. CONCLUSIONS: Universal MRSA surveillance of adults at hospital admission appears to be cost-effective at a wide range of prevalence and basic reproductive rate values. Individual hospitals and healthcare systems could compare their prevailing conditions (eg, the prevalence of MRSA colonization and MRSA transmission dynamics) with the benchmarks in our model to help determine their optimal local strategies.

Staphylococcus aureus vaccine for orthopedic patients: an economic model and analysis.

To evaluate the potential economic value of a Staphylococcus aureus vaccine for pre-operative orthopedic surgery patients, we developed an economic computer simulation model. At MRSA colonization rates as low as 1%, a $50 vaccine was cost-effective [or=30%, and a $100 vaccine at vaccine efficacy >or=70%. High MRSA prevalence (>or=25%) could justify a vaccine price as high as $1000. Our results suggest that a S. aureus vaccine for the pre-operative orthopedic population would be very cost-effective over a wide range of MRSA prevalence and vaccine efficacies and costs.