Universal screening for MRSA is an important next step

Thursday, October 16, 2008

With a quarter of NHS bodies failing to meet basic standards of infection control, the chief inspector of infection control at the Department of Health, Professor Brian Duerden, outlines the challenges of introducing universal screening for all patients and the benefits that will come from it

The three year programme on prevention and control of Methicillin-resistant Staphylococcus aureus (MRSA) infection has had a major impact on healthcare associated infections (HCAI) in the NHS. The very challenging target to halve the number of MRSA bacteraemias (bloodstream infections) by April-June 2008, which many thought to be impossible, was achieved, with the figures published in September showing a 57% reduction. However, we must not rest on this achievement; it is clear that MRSA infections can be reduced further and the pressure must be kept up for continued improvement.

An important plank in the next phase of the programme is screening. In October 2007, it was announced that all patients admitted to NHS hospitals would be screened for MRSA,¹ building on the screening procedures in place for selected patients in many hospitals. Screening is to be in place for all elective admissions by March 2009 and for all admissions by March 2011 at the latest, although it is expected that many non-elective admissions will be being screened before then. This extended the guidance issued as part of the Saving Lives package in September 2006,² which recommended a risk-based approach to screening to take in: high-risk surgical patients (at pre-admission clinics for elective operations); renal dialysis patients; those admitted to critical care units; high-risk medical admissions; and transfers from other hospitals and nursing or care homes. Trusts were also advised to consider screening emergency medical admissions. Detailed implementation was left to local decision.

What is screening?
The normal habitat of S. aureus, including MRSA, is the human nose and skin. Around 30% of the population are colonised with S. aureus; of these, about 10% have MRSA, ie. 3% of the general population, but this percentage is much higher in those with close healthcare links – frequent hospital attendance, nursing and care home residents, etc. Amongst hospital admissions, 6-10% of patients have been found to be colonised. Screening involves collecting swabs from the nose and other skin sites from patients, usually with no clinical evidence of MRSA infection, and examining them by microbiological tests to detect MRSA. Action can then be taken to give decolonisation treatment and, if possible, isolate patients when they are found to be colonised; these actions are an essential part of the screening package.

What is decolonisation?
When a patient is found to be MRSA-positive, they should be treated with an antibacterial nasal cream, body wash and shampoo applied over five days. They should also use clean underclothes, bedding and towels to reduce the chance of recontamination. This treatment is very effective in reducing the detectable carriage of MRSA in the short term, ie. it reduces the immediate MRSA bioburden, although in the longer term, the eradication rate for carriage may be as low as 60% after six months. However, the crucial period for preventing MRSA HCAI is the immediate period when the patient is undergoing their clinical interventions and treatments.

Why are we introducing universal screening?
Colonisation with MRSA generally precedes the development of clinical infection. A colonised patient is at risk of developing an infection themselves, such as a bacteraemia introduced through an intravenous line or a post-surgical wound infection. They are also a potential source of transmission of MRSA to other patients who may then develop an infection. Isolation of MRSA-positive patients where possible and appropriate, together with early decolonisation treatment, reduces the risk to the individual and the risk to others from transmission.

The evidence for implementing universal screening was based on: the first principle that colonisation precedes infection; together with the effectiveness of the 'Search and Destroy' policies of countries such as the Netherlands; the analysis conducted by the Scottish Executive study, which indicated that universal screening should reduce infection rates and reduce population carriage rates whereas a risk-based assessment would miss too many MRSA-positive admissions³; and the experience of NHS trusts that had already implemented more extensive screening.

What do we hope to achieve?
The primary aim is to reduce the incidence of MRSA infections with their initial morbidity and mortality, increased length of stay and potential long-term disability. This will come from reduced risk of infection in those found to be colonised, reduced risk of cross-infection to others and an overall reduction in the MRSA colonisation rate in the population, especially those with repeated and multiple links to healthcare facilities. This will also help restore public confidence in the NHS and reduce the NHS spend on treating HCAI caused by MRSA, releasing more funding for more 'positive' healthcare delivery.

How should we do it?
The implementation of MRSA screening and decolonisation has four main organisational facets: collection of the screening swabs; testing the swab for the presence of MRSA; delivering the decolonisation regimen for positive patients; and organising patient pathways to accommodate screening, decolonisation and isolation as necessary.

For elective admissions, it is often possible to collect the screening swabs at a pre-admission clinic. When a patient is found to be MRSA-positive, they can then receive decolonisation treatment before admission. However, where pre-admission arrangements are made in primary care settings, the screening and decolonisation may need to be organised through the primary care providers. There is also a need for secondary and primary care co-operation if screening is done at a hospital clinic but when the positive result is known, the patient is better served by obtaining the decolonisation treatments from their primary care practice.

The laboratory testing method should be determined by the speed of result required, the laboratory facilities available and the impact on patient flows. All tests are based on the detection of MRSA in swabs taken from the nose, with or without other skin sites such as groin or axilla, by conventional bacteriological culture, rapid enrichment and detection, or molecular (polymerase chain reaction - PCR) detection of MRSA genes. Direct plating of the swab on selective agar in the laboratory gives a result in 24-48 hours. It is less sensitive but quicker than enrichment in broth culture before plating, which takes 48-72 hours to give a result. However, swabs can be placed in enrichment broth at the point they are collected and then sent to the laboratory, which can reduce the time gap to 24 hours for a negative result, but still at least 48 hours for a positive test. A rapid enrichment culture with electromagnetic harvesting of MRSA and detection by ATP bioluminescence can give a result in about five hours. PCR detection of MRSA, generally referred to as the rapid method, generally takes about two hours of laboratory time, although reducing this time and potentially making the test available at point of care as well as in laboratories is becoming a feasible possibility. Decisions on what method to use have to be made locally.

For non-elective admissions, the decision on testing regimen and methodology is more complex and needs to be closely integrated with the organisation of patient flows. Where there are difficulties with isolation or segregation of patients while awaiting test results, the quicker a result can be provided, the sooner scarce isolation facilities can be freed up when patients are shown to be MRSA-negative. Where all patients can be treated as if positive, the result may be less urgent.

Conclusion
The implementation of universal screening for MRSA is a significant challenge for the NHS but carries the potential for important gains in helping reduce further the impact of MRSA infections on patients and on the delivery of healthcare.

1 Department of Health, 'Our NHS, Our Future'. NHS next stage review: interim report October 2007. www.dh.gov.uk/en/Publicationsandstatistics/Publications/PublicationsPolicyAndGuidance/DH_079077
2 Department of Health. Screening for Methicillin-resistant Staphylococcus aureus (MRSA) colonisation: a strategy for NHS trusts: a summary of best practice, 2006. www.dh.gov.uk/reducingmrsa
3 HTA Report 9; Ritchie K, Bradbury I, Craig J et al., The clinical and cost-effectiveness of screening for Methicillin-resistant Staphylococcus aureus (MRSA). NHS Quality Improvement Scotland 2007. www.nhshealthquality.org