Major NZ Study Into MRSA Published Internationally

Major NZ Study Into MRSA Published Internationally

ESR | 29 April 2013

• A copy of the full report is available on-line here including graphs showing the study’s key findings.

The results of the first study to systematically assess the clinical and molecular epidemiology and burden of MRSA (methicillin-resistant Staphylococcus aureus) from New Zealand have today been published in the International PLOS ONE Scientific Journal.

The study, led by the ESR and authored by ESR Clinical Microbiologist, Dr Deborah Williamson and ESR Senior Scientist Helen Heffernan, found that while Community- Associated MRSA (CA-MRSA) rates in New Zealand are increasing, they are generally low in comparison to other countries and have remained so for several years.

The research team analysed seven years of data between 2005 and 2011 from the national MRSA survey undertaken each year by ESR. Building on ESR’s regular surveillance, the research team used hospital admission data recorded by the New Zealand Ministry of Health to look at additional demographic data such as ethnicity, number of previous hospitalisations in the preceding year, and socioeconomic status based on the New Zealand deprivation index (NZDep).

Dr Williamson said that for clinicians and patients it’s encouraging that the rates remain comparatively low. “The data is very helpful in highlighting the groups affected by MRSA, and it also provides valuable information for health care providers on the circulating strains. As a country we should be encouraged that we have the capacity to do this type of surveillance so well.”

The report published today found several notable demographic and epidemiological findings including:

• Between 2005 and 2011 the rate of MRSA isolation from clinical specimens across the population increased from 8.6 to 18 per 100,000 people.

• When MRSA first arose globally around 20 years ago, it was a ‘hospital bug’. MRSA now appears to have become more associated with infections in people in the community. The study found this was also the situation in New Zealand, with a significant increase in Community-Associated MRSA in recent years in this country. This was largely due to two CA-MRSA clones, ST5-IV (AK3 MRSA) and ST30-IV (South-West Pacific MRSA).

• The ST5-IV MRSA clone was identified for the first time in the 2005 survey, and rapidly became the predominant Community-Associated MRSA strain in New Zealand.

• The shift into the community has been accompanied by a rise in cases amongst younger age groups, especially in recent years.

• There have been changes in the type of strains that are most common as Community-Associated MRSA has become more prevalent.

• The less rapid increase in Hospital-Associated MRSA could be the result of an increased focus of prevention measures in hospitals to combat bacteria such as MRSA.

• MRSA rates were significantly higher in Maori and Pacific Island populations. This is in keeping with findings for other infectious diseases where these populations carry a greater burden. Māori and Pacific Peoples ethnic groups disproportionately carried the burden of Community-Associated MRSA.

• New Zealand’s MRSA surveillance system detected new strains of MRSA in circulation.

Dr Williamson said the study would not have been possible without New Zealand’s national surveillance system to comprehensively monitor MRSA, which many countries do not have. “This system allows us to do this important research into MRSA because isolates and data are collected consistently each year, and from all diagnostic microbiology laboratories in New Zealand, providing a nationally representative profile of the epidemiology of MRSA.”

The study identified several ‘successful and virulent MRSA strains’ from other geographic settings, including ST93-IV (Queensland CA-MRSA), ST8-IV (USA300) and ST772-V (Bengal Bay MRSA). Dr Williamson said ongoing molecular surveillance is essential to prevent these MRSA strains becoming endemic in the New Zealand healthcare setting. “We are extremely fortunate in New Zealand to have a coordinated national surveillance system, which allows us to undertake this research to get a complete picture of this disease, which will inform decisions about how to prevent its spread and treat those who do become infected.”

ESR Senior Scientist, Helen Heffernan also said the study confirmed the importance of the monitoring in detecting new strains of MRSA to ensure those caring for patients in hospital or community environments can manage their care and treatment options accordingly.

Although the researchers found a significant increase in Community-Associated MRSA, they say that this may reflect an overall larger increase in Staphylococcus aureus infections, which has also been reported in other countries such as Australia and the US.

Helen Heffernan said that initially in most parts of the world MRSA was considered a ‘hospital bug’, but over the last decade this bacterium has been increasingly associated with infections in the community. “Most of the increase here in recent years has been due to the spread of a particular strain, ST5-IV, that is associated with community infections. The ST5-IV clone rapidly emerged over the study period and displaced ST30-IV as the dominant CA-MRSA clone,” she said.

Over the last three years ESR has received dedicated funding from the Ministry of Health to increase the testing and surveillance of antimicrobial-resistance bacteria like MRSA. Antimicrobial resistance testing has so far increased by 26% as a result of the new funding.

ENDS

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