Editorials
Infectious diseases Environmental health
Volume 207 - Issue 9

The changing face of methicillin-resistant Staphylococcus aureus infections

Authors:  Alistair T Leanord and John Coia

Med J Aust 2017; 207 (9): 379-380. || doi: 10.5694/mja17.00641
Published online: 6 November 2017
Further success in controlling MRSA will require adapting our tactics to its shifting epidemiology
Download PDF (483 KB)
Share: Share on Blue Sky Share on Facebook Share on LinkedIn Share by email

Further success in controlling MRSA will require adapting our tactics to its shifting epidemiology

There is an ongoing global endeavour to reduce the incidence of methicillin-resistant Staphylococcus aureus (MRSA) infections in health care settings. The major specific focus has been reducing MRSA transmission in hospitals, applying a combination of admission screening, isolation, and decolonisation, an approach allied to standard infection control precautions.1 In several countries this has significantly reduced the rate of serious MRSA infections, defined as the proportion of S. aureus bacteraemias that are methicillin-resistant; the United Kingdom, for example, has experienced an almost 90% reduction in MRSA bacteraemias over ten years.2 Similarly large reductions in MRSA rates have been reported in Australia.3,4

Despite this success, MRSA is still associated with considerable burdens of morbidity and mortality, much of which is generally acknowledged to be preventable.5 However, we have also seen a change in the epidemiology of MRSA, with an increasing contribution from sources previously considered to be of limited importance, as well as from previously unknown sources of infection. Studies in Spain, South Korea and the Netherlands have identified previously unrecognised MRSA strains and transmission events outside traditional hospital settings.6-8 There is also increasing recognition of significant animal reservoirs of MRSA that serve both as an ecologic sump for transmission and a further site for the development of antibiotic resistance.9,10

A number of studies have found that community infections now contribute a significant proportion of MRSA isolates.11 The importance of the community as a reservoir for MRSA is clearly shown by Agostino and his co-authors in their study published in this issue of the Journal,12 who report that more than 50% of patients from whom MRSA was isolated in the Hunter–New England region of New South Wales had not had any association with hospitals during the previous 12 months. The classic health care-associated patient risk factors for the carriage of MRSA are being an older patient, contact with the health care environment (including community and residential care homes), having an in situ intravascular device, antibiotic therapy during the previous 12 months, and the presence of comorbidities. It is now clear that, as the epidemiology of MRSA has shifted, so too have the risk factors associated with carriage, such that many patients no longer present with classic risk factors that can reliably be used to differentiate between high and low risk for MRSA carriage.13 The findings of Agostino and colleagues highlight the importance of MRSA carriage by the young, a group unlikely to have any major morbidity or other recognisable risk factor conventionally regarded as cornerstones of risk assessment.

Studies such as that of Agostino and colleagues highlight the increasingly complex evolutionary and epidemiological relationships, and the interchange between health care, community, and livestock/environmental reservoirs of MRSA. This blurring of traditional boundaries challenges many of our assumptions about the sources and spread of MRSA.

Where does this leave us in our continuing efforts to control MRSA? We have seen that identifying and controlling known transmission risks within hospitals have delivered reductions in health care-associated MRSA rates. The challenge, as Agostino and his co-authors correctly point out, is that controlling community-associated MRSA is now a priority. Community spread can be due to a number of factors, including the emergence of successful clones that expand within a geographic setting or into a new ecological niche, or which can cross species barriers.14 It may also reflect previously unrecognised transmission events, as revealed by the high discriminatory power of whole genome sequencing.15

Do we accept that any intervention to control a poorly understood dynamic in the community setting is doomed to failure? Is our only option to control the risk of MRSA at the hospital door with interventions that we know are beneficial, if stringently implemented? Or do we seek to gain a clearer understanding of MRSA transmission in the community, to identify novel pragmatic interventions that can be implemented outside a controlled health care environment?

The challenge will be to more fully understand the origins, evolution and spread of MRSA, how and why it affects (or doesn’t affect) healthy young adults or Indigenous people, and whether interventions such as decolonisation are appropriate or effective. Linking genomic, epidemiologic and clinical datasets on MRSA from human, animal and environmental sources provides powerful tools that allow us to investigate these questions. However, it is increasingly apparent that undertaking these studies, particularly at a national level, requires us to approach MRSA control in the context of increased delivery of health care in the community, the need for better analysis of data from surveillance systems, and the financial ability to respond to these challenges.

Authors

  • Alistair T Leanord1
  • John Coia2
  • 1. NHS Greater Glasgow and Clyde, Glasgow, Scotland, United Kingdom
  • 2. Scottish Microbiology Reference Laboratories, Glasgow, Scotland, United Kingdom

Correspondence: alistair.leanord@ggc.scot.nhs.uk

Competing interests

No relevant disclosures.

References

Provenance: Commissioned; externally peer reviewed.

View this article on Wiley Online Library