Universal screening for meticillin-resistant Staphylococcus aureus in acute care: risk factors and outcome from a multicentre study

SHEA/IDSA/APIC Practice Recommendation: Strategies to prevent methicillin-resistant Staphylococcus aureus transmission and infection in acute-care hospitals: 2022 Update

Previously published guidelines have provided comprehensive recommendations for detecting and preventing healthcare-associated infections (HAIs). The intent of this document is to highlight practical recommendations in a concise format designed to assist acute-care hospitals in implementing and prioritizing efforts to prevent methicillin-resistant Staphylococcus aureus (MRSA) transmission and infection. This document updates the "Strategies to Prevent Methicillin-Resistant Staphylococcus aureus Transmission and Infection in Acute Care Hospitals" published in 2014.1 This expert guidance document is sponsored by the Society for Healthcare Epidemiology of America (SHEA). It is the product of a collaborative effort led by SHEA, the Infectious Diseases Society of America (IDSA), the Association for Professionals in Infection Control and Epidemiology (APIC), the American Hospital Association (AHA), and The Joint Commission, with major contributions from representatives of a number of organizations and societies with content expertise.

Universal admission screening: a potential game-changer in hospitals with high prevalence of MRSA

INTRODUCTION

Despite the perception that meticillin-resistant Staphylococcus aureus (MRSA) is now under control in high-income countries, global prevalence remains high, even increasing in some regions. Universal admission screening and decolonization has been instituted in some hospitals to attempt control but the practice remains controversial.

METHODS

In 2014, Mater Dei Hospital in Malta introduced a universal admission screening policy, utilizing a novel, centralized and customized approach to achieve high compliance and low cost. Admissions are screened nasally by designated staff using chromogenic media, irrespective of risk factors. Carriers are decolonized without concurrent isolation or contact precautions. In this study, longitudinal, quasi-experimental evaluation was undertaken using time series analysis to analyse the impact of the intervention on the proportion of MRSA among clinical S. aureus isolates (%MRSA) and incidence per 1000 bed-days. A cost-utility analysis was also attempted to identify approximate quality-adjusted life years (QALYs) gained.

RESULTS

A transfer function model approach concluded that the intervention had a significant effect on both %MRSA and incidence. Six years following its introduction, the screening programme had led to an overall 43% long-term reduction in %MRSA from pre-screening levels [R²=0.687; Bayesian information criterion (BIC)=4.063], translating to a decrease in incidence of approximately 0.56 cases/1000 bed-days (R²=0.633, BIC=-3.063). No correlation was identified with consumption of antibiotics or alcohol hand rub. The annual cost-benefit of the programme was calculated at €1058 per QALY gain per year.

CONCLUSION

The universal admission screening and decolonization intervention was successful and cost-effective in this high-endemicity setting. It facilitated improvement in the prevalence of MRSA, achieving reduction levels rarely reported by Mediterranean hospitals.

Development and external validation of a clinical prediction model for MRSA carriage at hospital admission in Southeast Lower Saxony, Germany

In countries with low endemic Methicillin-resistant Staphylococcus aureus (MRSA) prevalence, identification of risk groups at hospital admission is considered more cost-effective than universal MRSA screening. Predictive statistical models support the selection of suitable stratification factors for effective screening programs. Currently, there are no universal guidelines in Germany for MRSA screening. Instead, a list of criteria is available from the Commission for Hospital Hygiene and Infection Prevention (KRINKO) based on which local strategies should be adopted. We developed and externally validated a model for individual prediction of MRSA carriage at hospital admission in the region of Southeast Lower Saxony based on two prospective studies with universal screening in Braunschweig (n = 2065) and Wolfsburg (n = 461). Logistic regression was used for model development. The final model (simplified to an unweighted score) included history of MRSA carriage, care dependency and cancer treatment. In the external validation dataset, the score showed a sensitivity of 78.4% (95% CI: 64.7-88.7%), and a specificity of 70.3% (95% CI: 65.0-75.2%). Of all admitted patients, 25.4% had to be screened if the score was applied. A model based on KRINKO criteria showed similar sensitivity but lower specificity, leading to a considerably higher proportion of patients to be screened (49.5%).

Sustained fall in inpatient MRSA prevalence after a video-reflexive ethnography project; an observational study

BACKGROUND

Maintaining optimal infection prevention and control (IPC) in a busy, clinical environment is challenging. Video-reflexive ethnography (VRE) is a collaborative, interventionist approach to practice improvement. We hypothesised that giving clinicians opportunities to view and reflect on video footage of everyday ward activities would raise awareness of, and suggest strategies to reduce, pathogen transmission risks. We undertook a VRE project, between March and September 2013, in two tertiary hospital surgical wards, with persistently high methicillin resistant Staphylococcus aureus (MRSA) endemicity, despite previous IPC interventions.

METHODS

This study was a retrospective/prospective observational study, using interrupted time-series analyses, to assess the effects of the VRE project on hand hygiene compliance, inpatient MRSA infections (newly infected patients, per 1000 occupied bed days) and inpatient MRSA colonisation prevalence, measured by serial point prevalence surveys. Follow-up continued until June 2016.

RESULTS

The VRE project was associated with changes in IPC behaviour and outcomes. Hand hygiene compliance increased (from 62% to 75%; p < 0.0001) and MRSA colonisation prevalence decreased significantly, in both wards (baseline 42%; average post-VRE 12%; p=<0.0001), MRSA infection rate decreased in one ward. Interpretation of results was complicated by a potential confounding effect of unplanned environmental hydrogen peroxide decontamination (HPD). Improved hand hygiene compliance was a predicted outcome of VRE, but also a potential contributor to reduced MRSA transmission.

CONCLUSION

Separate contributions of VRE (the intervention), HPD and hand hygiene compliance were uncertain, but their combined effect was significantly reduced MRSA endemicity, which previously had been resistant to attempted IPC interventions.

Ambulatory screening and decontamination to prevent Staphylococcus aureus complications in patients undergoing elective surgery (STAUfrei): study protocol for a controlled intervention study

BACKGROUND

Surgical site infections (SSI) are the most common health care associated infections in German acute hospitals and can result in prolonged hospital stays, increased use of antibiotics and utilisation of care. Staphylococcus aureus bacteria (methicillin-resistant S Aureus (MRSA) and methicillin-susceptible S Aureus (MSSA)) are amongst the most prominent causes of SSI. While up to 90% of documented S Aureus colonization is already detectable prior to hospital admission, the majority of hygiene measures in Germany is focused on the hospital setting. It is hypothesized that early detection and decontamination of S Aureus colonization in primary care can prevent health care associated infections and reduce the number of S Aureus isolates in the hospital setting.

METHODS

This study is a controlled interventional study (N = 13,260) with a pre-post comparison. The intersectoral intervention (over 2 years) will encompass the following elements: ambulatory detection and decontamination of MRSA and MSSA prior to elective surgery combined with a structured follow-up care. Patients from the control group will be screened in the hospital setting, in accordance with the standard operating procedure (SOP) in routine care. The primary endpoint is the reduction of MRSA and MSSA colonization upon hospital admission. Secondary endpoints are complication rate (SSI), length of stay, recolonization of patients (3 and 6 months after release), patient and provider satisfaction, patient compliance and cost development.

DISCUSSION

In case of positive results, the chance of a widespread uptake and implementation in routine care are considered high. The active involvement of primary care providers in the implementation of screening and decontamination as well as follow-up care is a unique feature of this study. The positive resonance of primary care providers during the recruitment phase highlights the relevance of the topic to the participating actors. These efforts are coupled with patient education and specifically trained medical staff, promising a sustained impact. The STAUfrei care pathway can homogenize current practices in routine care and provide a template for further intersectoral cooperation.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS), DRKS00016615. Registered on April 1st, 2019.

Long-term Mortality After Rapid Screening and Decolonization of Staphylococcus Aureus Carriers: Observational Follow-up Study of a Randomized, Placebo-controlled Trial

OBJECTIVE

To identify patients who benefit most from Staphylococcus aureus screening and decolonization treatment upon admission.

BACKGROUND

S. aureus carriers are at increased risk of developing surgical-site infections with S. aureus. Previously, we demonstrated in a randomized, placebo-controlled trial (RCT) that these infections can largely be prevented by detection of carriage and decolonization treatment upon admission. In this study, we analyzed 1- and 3-year mortality rates in both treatment arms of the RCT to identify patient groups that should be targeted when implementing the screen-and-treat strategy.

METHODS

Three years after enrolment in the RCT, mortality dates of all surgical patients were checked. One- and 3-year mortality rates were calculated for all patients and for various subgroups.

RESULTS

After 3 years, 44 of 431 (10.2%) and 43 of 362 (11.9%) patients had died in the mupirocin/chlorhexidine and placebo groups, respectively. No significant differences in mortality rates were observed between the treatment groups or the subgroups according to type of surgery. In the subgroup of patients with clean procedures (382 cardiothoracic, 167 orthopedic, 61 vascular, and 56 other), mupirocin/chlorhexidine reduced 1-year mortality: 11 of 365 (3.0%) died in the mupirocin/chlorhexidine versus 21 of 301 (7.0%) in the placebo group [hazard ratio = 0.38 (95% CI: 0.18-0.81)].

CONCLUSIONS

Detection and decolonization of S. aureus carriage not only prevents S. aureus surgical-site infections but also reduces 1-year mortality in surgical patients undergoing clean procedures. Such patients with a high risk of developing S. aureus infections should therefore be the primary target when implementing the screen-and-treat strategy in clinical practice.

Strategies to Prevent Methicillin-ResistantStaphylococcus aureusTransmission and Infection in Acute Care Hospitals: 2014 Update

Previously published guidelines are available that provide comprehensive recommendations for detecting and preventing healthcare-associated infections (HAIs). The intent of this document is to highlight practical recommendations in a concise format designed to assist acute care hospitals in implementing and prioritizing their methicillin-resistantStaphylococcus aureus(MRSA) prevention efforts. This document updates “Strategies to Prevent Transmission of Methicillin-ResistantStaphylococcus aureusin Acute Care Hospitals,” published in 2008. This expert guidance document is sponsored by the Society for Healthcare Epidemiology of America (SHEA) and is the product of a collaborative effort led by SHEA, the Infectious Diseases Society of America (IDSA), the American Hospital Association (AHA), the Association for Professionals in Infection Control and Epidemiology (APIC), and The Joint Commission, with major contributions from representatives of a number of organizations and societies with content expertise. The list of endorsing and supporting organizations is presented in the introduction to the 2014 updates.

Risk and outcomes of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia among patients admitted with and without MRSA nares colonization

BACKGROUND

The risk of nosocomial methicillin-sensitive Staphylococcus aureus bacteremia in patients with nasal colonization on admission is 3-fold higher than in patients who are not colonized. Limited data on this question have been reported for methicillin-resistant S aureus (MRSA).

METHODS

This is an observational cohort study of patients admitted to a tertiary care medical center from October 1, 2007-September 30, 2013, who underwent active screening for nasal colonization with MRSA.

RESULTS

There were 29,371 patients who underwent screening for nasal MRSA colonization; 3,262 (11%) were colonized with MRSA. There were 32 cases of MRSA bacteremia among colonized patients, for an incidence of 1%. Thirteen cases of bacteremia occurred in non-MRSA-colonized patients, for an incidence of 0.05%. The odds of developing MRSA bacteremia for patients who were nasally colonized with MRSA compared with those who were not colonized were 19.89. There was no difference between colonized and noncolonized subjects with bacteremia in all-cause mortality at 30 days or 1 year.

CONCLUSIONS

In a setting with active screening for MRSA, the risk of MRSA bacteremia is 19.89-fold higher among colonized than noncolonized patients.

The relationship between hand hygiene and health care-associated infection: it's complicated

The reasoning that improved hand hygiene compliance contributes to the prevention of health care-associated infections is widely accepted. It is also accepted that high hand hygiene alone cannot impact formidable risk factors, such as older age, immunosuppression, admission to the intensive care unit, longer length of stay, and indwelling devices. When hand hygiene interventions are concurrently undertaken with other routine or special preventive strategies, there is a potential for these concurrent strategies to confound the effect of the hand hygiene program. The result may be an overestimation of the hand hygiene intervention unless the design of the intervention or analysis controls the effect of the potential confounders. Other epidemiologic principles that may also impact the result of a hand hygiene program include failure to consider measurement error of the content of the hand hygiene program and the measurement error of compliance. Some epidemiological errors in hand hygiene programs aimed at reducing health care-associated infections are inherent and not easily controlled. Nevertheless, the inadvertent omission by authors to report these common epidemiological errors, including concurrent infection prevention strategies, suggests to readers that the effect of hand hygiene is greater than the sum of all infection prevention strategies. Worse still, this omission does not assist evidence-based practice.

Systematic literature analysis and review of targeted preventive measures to limit healthcare-associated infections by meticillin-resistant Staphylococcus aureus

Meticillin-resistant Staphylococcus aureus (MRSA) is a major cause of healthcare-associated infections in Europe. Many examples have demonstrated that the spread of MRSA within healthcare settings can be reduced by targeted infection control measures. The aim of this systematic literature analysis and review was to summarise the evidence for the use of bacterial cultures for active surveillance the benefit of rapid screening tests, as well as the use of decolonisation therapies and different types of isolation measures. We included 83 studies published between 2000 and 2012. Although the studies reported good evidence supporting the role of active surveillance followed by decolonisation therapy, the effectiveness of single-room isolation was mostly shown in non-controlled studies, which should inspire further research regarding this issue. Overall, this review highlighted that when planning the implementation of preventive interventions, there is a need to consider the prevalence of MRSA, the incidence of infections, the competing effect of standard control measures (e.g. hand hygiene) and the likelihood of transmission in the respective settings of implementation.

Implications of targeted versus universal admission screening for meticillin-resistant Staphylococcus aureus carriage in a London hospital

Universal admission screening for meticillin-resistant Staphylococcus aureus (MRSA) has been performed in England since 2010. We evaluated the predictive performance of a regression model derived from the first year of universal screening for detecting MRSA at hospital admission. If we had used our previous targeted screening policy, 75% fewer patients (21,699 per year) would have been screened. However, this would have identified only ~55% of all MRSA carriers, 65% of healthcare-associated MRSA strains, and 40% of community-associated strains. Failing to identify ~45% of patients (262 per year) carrying MRSA at hospital admission may have implications for MRSA control.

Screening for methicillin-resistant Staphylococcus aureus: a comparative effectiveness review

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of health care-associated infections. Although the evidence in support of MRSA screening has been promising, a number of questions remain about the effectiveness of active surveillance.

METHODS

We searched the literature for studies that examined MRSA acquisition, MRSA infection, morbidity, mortality, harms of screening, and resource utilization when screening for MRSA carriage was compared with no screening or with targeted screening. Because of heterogeneity of the data and weaknesses in study design, meta-analysis was not performed. Strength of evidence (SOE) was determined using the system developed by the Grading of Recommendations Assessment, Development and Evaluation Working Group.

RESULTS

One randomized controlled trial and 47 quasi-experimental studies met our inclusion criteria. We focused on the 14 studies that addressed health care-associated outcomes and that attempted to control for confounding and/or secular trends, because those studies had the potential to support causal inferences. With universal screening for MRSA carriage compared with no screening, 2 large quasi-experimental studies found reductions in health care-associated MRSA infection. The SOE for this finding is low. For each of the other screening strategies evaluated, this review found insufficient evidence to determine the comparative effectiveness of screening.

CONCLUSIONS

Although there is low SOE that universal screening of hospital patients decreases MRSA infection, there is insufficient evidence to determine the consequences of universal screening or the effectiveness of other screening strategies.

Screening cultures for detection of methicillin-resistant Staphylococcus aureus in a population at high risk for MRSA colonisation: identification of optimal combinations of anatomical sites

This retrospective study analysed the diagnostic yield of single-site, two-site, and three-site anatomical surveillance cultures in a population of 4,769 patients at high risk for methicillin-resistant Staphylococcus aureus (MRSA) colonisation. Cultures of seven anatomical sites were used as the gold standard against which to measure the sensitivity of MRSA detection. Detection rates for the seven single-sites, 21 two-site, and 35 three-site combinations are presented. Single-site swabbing only detected 50.5% (nose) of total cases, while three-site surveillance achieved a 92% (groin + nose + throat) sensitivity of detection at best. It is recommended that at least three anatomical sites should be screened for MRSA colonisation in these high-risk patients.

Clinical significance of methicillin-resistant Staphylococcus aureus colonization on hospital admission: one-year infection risk

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization among inpatients is a well-established risk factor for MRSA infection during the same hospitalization, but the long-term risk of MRSA infection is uncertain. We performed a retrospective cohort study to determine the one-year risk of MRSA infection among inpatients with MRSA-positive nasal polymerase chain reaction (PCR) tests confirmed by positive nasal culture (Group 1), patients with positive nasal PCR but negative nasal culture (Group 2), and patients with negative nasal PCR (Group 3).

METHODOLOGY/PRINCIPAL FINDINGS

Subjects were adults admitted to a four-hospital system between November 1, 2006 and March 31, 2011, comprising 195,255 admissions. Patients underwent nasal swab for MRSA PCR upon admission; if positive, nasal culture for MRSA was performed; if recovered, MRSA was tested for Panton-Valentine Leukocidin (PVL). Outcomes included MRSA-positive clinical culture and skin and soft tissue infection (SSTI). Group 1 patients had a one-year risk of MRSA-positive clinical culture of 8.0% compared with 3.0% for Group 2 patients, and 0.6% for Group 3 patients (p<0.001). In a multivariable model, the hazard ratios for future MRSA-positive clinical culture were 6.52 (95% CI, 5.57 to 7.64) for Group 1 and 3.40 (95% CI, 2.70 to 4.27) for Group 2, compared with Group 3 (p<0.0001). History of MRSA and concurrent MRSA-positive clinical culture were significant risk factors for future MRSA-positive clinical culture. Group 1 patients colonized with PVL-positive MRSA had a one-year risk of MRSA-positive clinical culture of 10.1%, and a one-year risk of MRSA-positive clinical culture or SSTI diagnosis of 21.7%, compared with risks of 7.1% and 12.5%, respectively, for patients colonized with PVL-negative MRSA (p = 0.04, p = 0.005, respectively).

CONCLUSIONS/SIGNIFICANCE

MRSA nasal colonization is a significant risk factor for future MRSA infection; more so if detected by culture than PCR. Colonization with PVL-positive MRSA is associated with greater risk than PVL-negative MRSA.

Methicillin-resistant Staphylococcus aureus screening as a patient safety initiative: using patients' experiences to improve the quality of screening practices

AIMS AND OBJECTIVES

To explore the patient experience and acceptability of methicillin-resistant Staphylococcus aureus screening of inpatient admissions to acute hospital settings.

BACKGROUND

Prevention of healthcare-associated infections such as methicillin-resistant Staphylococcus aureus is a major patient safety concern internationally. Screening of patients for methicillin-resistant Staphylococcus aureus colonisation is becoming a routine aspect of hospital admission; however, evidence of the patient experience and acceptability of methicillin-resistant Staphylococcus aureus screening is limited.

DESIGN

A mixed-methods study set in six acute care hospitals in three Scottish regions.

METHODS

Data collection involved postdischarge self-report survey of patients who had been screened (n = 54) and qualitative patient interviews (n = 10). Theoretical constructs derived from the Health Belief Model and Theory of Planned Behaviour used in analysis.

RESULTS

Findings indicated that methicillin-resistant Staphylococcus aureus screening was broadly acceptable to patients. The experience of screening did not appear to be problematic; responses demonstrate that screening provided reassurance and generated confidence that health organisations were tackling healthcare-associated infections. Patients were less positive regarding the provision of information, the possibility of refusing a screen and the consequences of a positive test result. Furthermore, there were indications that patients wanted to be told the results of the screen and strong support for screening of hospital staff.

CONCLUSIONS

Analysis of constructs from our theoretical frameworks provides evidence that attitudes were largely positive; responses indicate a belief in the beneficial impact of methicillin-resistant Staphylococcus aureus screening for patients and the wider community. However, it is important that health professionals continually assess the patient experience of 'routine' aspects of health care such as MRSA screening.

RELEVANCE TO CLINICAL PRACTICE

The findings from this study suggest that while methicillin-resistant Staphylococcus aureus screening is generally acceptable to patients as a regular patient safety initiative, to enhance the quality of the patient experience, clinicians should consider the timing, content and effectiveness of information provision.

Low prevalence of meticillin-resistant Staphylococcus aureus carriage at hospital admission: implications for risk-factor-based vs universal screening

BACKGROUND

There is debate over the optimal policy for detecting meticillin-resistant Staphylococcus aureus (MRSA) colonization at hospital admission. The emergence of community-associated (CA)-MRSA may compromise targeted screening strategies based on risk factors for healthcare-associated (HA)-MRSA.

AIM

To determine the prevalence of MRSA colonization at admission, and the genotype and molecular epidemiology of the strains involved.

METHODS

A 12-month observational study was performed at a 1200-bed London tertiary referral hospital from 1 April 2008 to 1 March 2009. All available MRSA isolates were genotyped by spa and staphylococcal cassette chromosome mec (SCCmec) typing.

FINDINGS

The overall MRSA colonization rate was 2.0% of 28,892 admissions (range 6.6% in critical care to 0.8% in obstetrics/gynaecology/neonatology). The overall frequency of previously unknown carriage of MRSA on admission was 1.4%. Most colonizing strains were epidemic HA-MRSA-15 and -16. However, heterogeneous CA strains accounted for 18% of recovered isolates, including 37.5% of MRSA from accident and emergency and 23.1% of MRSA from surgery. The CA-MRSA strain types had significantly different epidemiological associations from the HA-MRSA strains, so risk factors used for the identification of HA-MRSA may not detect CA-MRSA reliably.

CONCLUSION

The low rate of HA-MRSA in the UK increases the relative proportion due to CA-MRSA, for which conventional risk-factor-based screening strategies may be less effective. Cost-benefit analyses of universal MRSA admission screening will need to take account of this new epidemiology.

Prevalence of and risk factors for MRSA colonization in HIV-positive outpatients in Singapore

BACKGROUND

Whilst there have been studies on the risks and outcomes of MRSA colonization and infections in HIV-positive patients, local data is limited on the risk factors for MRSA colonization among these patients. We undertook this study in a tertiary HIV care centre to document the risk factors for colonization and to determine the prevalence of MRSA colonization among HIV-positive outpatients in Singapore.

METHODS

This was a cross-sectional study in which factors associated with MRSA positivity among patients with HIV infection were evaluated. A set of standardized questionnaire and data collection forms were available to interview all recruited patients. Following the interview, trained nurses collected swabs from the anterior nares/axilla/groin (NAG), throat and peri-anal regions. Information on demographics, clinical history, laboratory results and hospitalization history were retrieved from medical records.

RESULTS

MRSA was detected in swab cultures from at least 1 site in 15 patients (5.1%). Inclusion of throat and/or peri-anal swabs increased the sensitivity of NAG screening by 20%. Predictors for MRSA colonization among HIV-positive patients were age, history of pneumonia, lymphoma, presence of a percutaneous device within the past 12 months, history of household members hospitalized more than two times within the past 12 months, and a most recent CD4 count less than 200.

CONCLUSIONS

This study highlights that a proportion of MRSA carriers would have been undetected without multiple-site screening cultures. This study could shed insight into identifying patients at risk of MRSA colonization upon hospital visit and this may suggest that a risk factor-based approach for MRSA surveillance focusing on high risk populations could be considered.

Staphylococcus aureus: the enduring pathogen in surgery

Staphylococcus aureus is part of the normal bacterial flora of the upper respiratory tract, especially the nose, but it can colonise other sites, such as the skin. However, S. aureus is also the commonest cause of surgical site infection (SSI) and is a major cause of bloodstream infection (BSI). The development of staphylococcal infection arises from a combination of bacterial factors, e.g. production of toxins and host factors, including underlying patient disease, e.g. diabetes mellitus. The surveillance of SSI and BSI are increasingly components of national quality programmes to reduce healthcare-associated infection (HCAI) in the UK, Ireland and beyond and the proportion of S. aureus BSI due to methicillin-resistant S. aureus (MRSA) has declined in recent years but not necessarily that due to methicillin-susceptible S. aureus. However, the complexity and sophistication of the staphylococcal genome has enabled it to change and adapt to varying circumstances such as exposure to a new antibiotic, adherence to a biomedical device and transfer from an animal to a human host. The future will perhaps see more cases of community-acquired MRSA and which may become endemic in hospitals and cause HCAI, technology becoming available to rapidly detect, type and characterise isolates for resistance and virulence and finally greater efforts at local and national level to drive down infection rates. However, good surgical practice, education and audit supported by new technology will enable surgeons to meet the challenges ahead.

Nasal swab screening for methicillin-resistant Staphylococcus aureus--how well does it perform? A cross-sectional study

OBJECTIVE

To determine the proportion of methicillin-resistant Staphylococcus aureus (MRSA) detections identified by nasal swabbing using agar culture in comparison with multiple body site testing using agar and nutrient broth culture.

DESIGN

Cross-sectional study.

PATIENTS

Adult patients admitted to 36 general specialty wards of 2 large hospitals in Scotland.

METHODS

Patients were screened for MRSA via multiple body site swabs (nasal, throat, axillary, perineal, and wound/invasive device sites) cultured individually on chromogenic agar and pooled in nutrient broth. Combined results from all sites and cultures provided a gold-standard estimate of true MRSA prevalence.

RESULTS

This study found that nasal screening performed better than throat, axillary, or perineal screening but at best identified only 66% of true MRSA carriers against the gold standard at an overall prevalence of 2.9%. Axillary screening performed least well. Combining nasal and perineal swabs gave the best 2-site combination (82%). When combined with realistic screening compliance rates of 80%-90%, nasal swabbing alone probably detects just over half of true colonization in practice. Swabbing of clinically relevant sites (wounds, indwelling devices, etc) is important for a small but high-prevalence group.

CONCLUSIONS

Nasal swabbing is the standard method in many locations for MRSA screening. Its diagnostic efficiency in practice appears to be limited, however, and the resource implications of multiple body site screening have to be balanced against a potential clinical benefit whose magnitude and nature remains unclear.

Trends in Staphylococcus aureus bacteraemia and impacts of infection control practices including universal MRSA admission screening in a hospital in Scotland, 2006-2010: retrospective cohort study and time-series intervention analysis

OBJECTIVES

To describe secular trends in Staphylococcus aureus bacteraemia (SAB) and to assess the impacts of infection control practices, including universal methicillin-resistant Staphylococcus aureus (MRSA) admission screening on associated clinical burdens.

DESIGN

Retrospective cohort study and multivariate time-series analysis linking microbiology, patient management and health intelligence databases.

SETTING

Teaching hospital in North East Scotland.

PARTICIPANTS

All patients admitted to Aberdeen Royal Infirmary between 1 January 2006 and 31 December 2010: n=420 452 admissions and 1 430 052 acute occupied bed days (AOBDs).

INTERVENTION

Universal admission screening programme for MRSA (August 2008) incorporating isolation and decolonisation. PRIMARY AND SECONDARY MEASURES: Hospital-wide prevalence density, hospital-associated incidence density and death within 30 days of MRSA or methicillin-sensitive Staphylococcus aureus (MSSA) bacteraemia.

RESULTS

Between 2006 and 2010, prevalence density of all SAB declined by 41%, from 0.73 to 0.50 cases/1000 AOBDs (p=0.002 for trend), and 30-day mortality from 26% to 14% (p=0.013). Significant reductions were observed in MRSA bacteraemia only. Overnight admissions screened for MRSA rose from 43% during selective screening to >90% within 4 months of universal screening. In multivariate time-series analysis (R(2) 0.45 to 0.68), universal screening was associated with a 19% reduction in prevalence density of MRSA bacteraemia (-0.035, 95% CI -0.049 to -0.021/1000 AOBDs; p<0.001), a 29% fall in hospital-associated incidence density (-0.029, 95% CI -0.035 to -0.023/1000 AOBDs; p<0.001) and a 46% reduction in 30-day mortality (-15.6, 95% CI -24.1% to -7.1%; p<0.001). Positive associations with fluoroquinolone and cephalosporin use suggested that antibiotic stewardship reduced prevalence density of MRSA bacteraemia by 0.027 (95% CI 0.015 to 0.039)/1000 AOBDs. Rates of MSSA bacteraemia were not significantly affected by screening or antibiotic use.

CONCLUSIONS

Declining clinical burdens from SAB were attributable to reductions in MRSA infections. Universal admission screening and antibiotic stewardship were associated with decreases in MRSA bacteraemia and associated early mortality. Control of MSSA bacteraemia remains a priority.