Statistical bulletin: Deaths involving MRSA: England and Wales, 2006 to 2010

Key points

• Deaths involving MRSA fell by 38 per cent between 2009 and 2010 from 781 to 485
• There were 961 death certificates mentioning Staphylococcus aureus (including those not specifying meticillin resistance) in 2010
• In males rates for deaths involving MRSA fell from 11.7 to 6.8 per million population between 2009 and 2010
• For females rates decreased from 5.9 to 3.7 per million population between 2009 and 2010
• During 2006 to 2010 MRSA was involved in 0.2 per cent of deaths and 0.4 per cent of hospital deaths

Summary

This bulletin presents the latest figures for deaths where meticillin-resistant Staphylococcus aureus (MRSA) was mentioned on the death certificate: by sex, age group and place of death, in England and Wales. Figures are presented for deaths registered in 2010, with previously released figures for 2006 to 2009 for comparison purposes. Information is also given about the context and use of the statistics, and the method used to produce them.

Figure 1. Age-standardised mortality rates for deaths mentioning Staphylococcus aureus: by meticillin resistance, 2006 to 2010

England and Wales

Source: Office for National Statistics

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Background

The Staphylococcus aureus (S. aureus) family of bacteria, to which MRSA belongs, was first identified in the 1880s when doctors realised it was the most common cause of infected surgical wounds and could cause serious or sometimes fatal disease (Department of Health 2007).

S. aureus bacteria are commonly present on the human skin and in mucosa (for example inside the nose) without causing any problems. About 30 per cent of the general population are colonised (known as carriers) and one in ten of these (3 per cent) are carriers of MRSA. Infection occurs if there is an opportunity for the bacteria to enter the body, for example, through broken skin or a medical procedure.

If the bacteria enter the body, illnesses which range from mild to life-threatening may then develop (Health Protection Agency 2011a). These include skin and wound infections, infected eczema, abscesses or joint infections, infections of the heart valves (endocarditis), pneumonia and bacteraemia (blood stream infection). S. aureus also produces toxins which, if the bacteria contaminate incorrectly prepared food, can cause food poisoning, and they have also been linked with toxic shock syndrome. Some strains also produce another toxin called PVL, which tends to cause more severe disease.

Most strains of S. aureus are sensitive to the more commonly used antibiotics, and infections can be effectively treated. Some S. aureus bacteria are more resistant. Those resistant to the antibiotic meticillin are termed meticillin resistant Staphylococcus aureus (MRSA) and often require different types of antibiotic to treat them. Those that are sensitive to meticillin are termed meticillin sensitive Staphylococcus aureus (MSSA). MRSA and MSSA only differ in their degree of antibiotic resistance: other than that there is no real difference between them.

Actions to reduce levels of healthcare associated infections have been detailed in various reports (Department of Health 2003, 2007) and have been implemented in healthcare settings. These include better antibiotic prescribing, isolating and using gloves to treat infected patients, decontamination with skin and nose treatment prior to surgery if pre-screening shows MRSA carriage, and improved hand hygeine.

Use of the statistics

Figures on the number and rate of deaths from S. aureus and MRSA in England and Wales are used by various organisations, including the Department of Health (DH), the Health Protection Agency (HPA), and Public Health Wales for monitoring and evaluation purposes. They are also used by primary care organisations (PCOs), local health boards (LHBs) and individual healthcare establishments.

The Operating Framework for the NHS in England 2011/12 (Department of Health 2010) states:

• The NHS has made good progress in reducing MRSA bloodstream and Clostridium difficile infections. There is still scope to drive these and other healthcare associated infections (HCAIs) down further. NHS organisations should aim for a zero tolerance approach to all HCAIs and all organisations must identify and adjust plans so that they can operate at the level of the best. NHS providers and commissioners should ensure that their HCAI improvement plans deliver at least the level of performance set by the HCAI indicators.

Specifically, there are two HCAI measures which require PCOs in England to reduce the number of MRSA and C. difficile infections. Organisations with higher baseline rates are required to deliver larger reductions.

MRSA infections occurring in England are monitored monthly using data collected by the HPA. The latest figures show that a total of 1,481 cases of MRSA were reported across the NHS between April 2010 and March 2011 (2010/11) (Health Protection Agency 2011b). This represents a reduction of 22 per cent on the 1,898 cases of MRSA reported in 2009/10 and a 50 per cent reduction on the cases reported in 2008/09.

In Wales, surveillance of MRSA is managed by the Welsh Healthcare Associated Infection Programme (WHAIP), which is part of Public Health Wales. Figures for April 2009 to March 2010 (2009/10) show that there were 274 cases of MRSA reported (Public Health Wales 2011). This represents a reduction of 19 per cent on the 340 cases reported in 2008/09.

Deaths involving S. aureus and MRSA statistics have been produced by the Office for National Statistics (ONS) for 1993 onwards (see 'Methods' below for more information). Figures for recent years show a large decrease in the number and rate of deaths where S. aureus and MRSA were the underlying cause of death or were mentioned anywhere on the death certificate among both males and females. This finding is consistent with the incidence figures reported by the HPA and Public Health Wales. The decreases may be due to the actions taken to reduce healthcare associated infections described above.

Results

Number of deaths where Staphylococcus aureus or MRSA were mentioned on the death certificate

The number of death certificates in England and Wales mentioning S. aureus infection (including those specifying meticillin resistance (MRSA)) has decreased each year since 2006, where the figure peaked at 2,150 (Table 1). In 2010 there were 961 deaths involving S. aureus, 292 lower than the 1,253 recorded in 2009.

The number of death certificates mentioning MRSA also peaked in 2006 at 1,652. This figure has since decreased and fell to 485 in 2010. The percentage of deaths involving S. aureus which specified meticillin resistance was highest in 2008 at 82 per cent. This decreased to 62 per cent in 2009 and 50 per cent in 2010.

Figure 2. Number of death certificates mentioning Staphylococcus aureus: by meticillin resistance, 2006 to 2010

England and Wales

Source: Office for National Statistics

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On 33 per cent of death certificates which mentioned S. aureus in 2006, this infection was recorded as the underlying cause of death. For deaths involving MRSA, this infection was recorded as the underlying cause in 31 per cent of cases. In 2010 the percentage of death certificates mentioning S. aureus and MRSA which recorded these infections as the underlying cause fell to 24 per cent and 17 per cent respectively.

Mortality rates for deaths mentioning Staphylococcus aureus and MRSA

Most of the deaths involving S. aureus and MRSA occur among older people (Table 2). For the combined 2006 to 2010 period, age-specific mortality rates were highest in those aged 85 years and over. Male mortality rates for deaths mentioning S. aureus and MRSA in this age group were 652 and 527 per million population respectively. The respective rates for females were 315 and 251 per million.

During 2006 to 2010, the lowest age-specific mortality rates for deaths mentioning S. aureus and MRSA were among people aged under 45 years. For deaths in this age group where S. aureus was mentioned, the mortality rate was 2.6 and 2.0 per million for males and females respectively. The rate for deaths involving MRSA was 0.9 per million for males and 0.7 per million for females.

Between 2006 and 2010, age-standardised mortality rates were higher for males than females (Table 3). In males, rates for deaths mentioning S. aureus and MRSA peaked in 2006 at 35.7 and 26.8 per million respectively. In 2010, the rates decreased to 13.8 per million for S. aureus and 6.8 per million for MRSA.

Among females, mortality rates for deaths involving S. aureus and MRSA were highest in 2006 at 18.0 and 13.2 per million population respectively. Since then, rates have consistently fallen and decreased to 8.2 per million for S. aureus and 3.7 per million for MRSA in 2010.

Place of death

Due to improvements in the classification and coding of communal establishments, the place of death definition used by ONS has been revised. In particular, the NHS and non-NHS nursing home and private residential home categories have been replaced with local authority and non-local authority care home categories, which reflects current user needs. The allocation and coding of individual establishments to place of death categories is a continual exercise which will improve the quality of this new classification.

Between 2006 and 2010 deaths involving S. aureus and MRSA accounted for 0.3 per cent and 0.2 per cent respectively of all deaths in England and Wales (Table 4). Death certificates rarely specify the place where an infection was acquired, although the place of death is routinely recorded.

The majority of deaths in England and Wales occur in hospital. It is therefore expected that most deaths involving S. aureus and MRSA will occur in hospital. At present, ONS does not produce figures by individual hospital establishment.

During the 2006 to 2010 combined period, 90.8 per cent of deaths involving S. aureus and 88.5 per cent of deaths involving MRSA occurred in NHS hospitals. These represent 0.5 per cent and 0.4 per cent of all deaths that occurred in NHS hospitals respectively.

In the same period, 6.3 per cent of S. aureus deaths and 8.3 per cent of MRSA deaths occurred in care homes. Both figures represent 0.1 per cent of all deaths in care homes.

Results on the Office for National Statistics website

Data for deaths involving S. aureus and MRSA can be found in a Microsoft Excel workbook on the ONS website.

The workbook contains the following results for England and Wales:

• the number of death certificates with Staphylococcus aureus and MRSA mentioned and as the underlying cause of death, by country, 1993 to 2010

• the number of death certificates with Staphylococcus aureus and MRSA mentioned and as the underlying cause of death, by country and annual registration quarters, 1993 to 2010

• age-standardised mortality rates for deaths where Staphylococcus aureus and MRSA were mentioned on the death certificate, by country and sex, 1993 to 2010

Table 3. Age-standardised mortality rates for deaths mentioning S. aureus and MRSA: by sex, 2006 to 2010

Table source: Office for National Statistics

Table notes:

1. Figures for England and Wales include deaths of non-residents. Data for England and Wales separately exclude deaths of non-residents.

Methods

All deaths are coded by ONS according to the International Classification of Diseases (ICD) supplied by the World Health Organisation (WHO). Since 1993, ONS has stored the text of death certificates on a database, along with all the ICD coding relating to causes identified on the death certificate. ONS uses a combination of ICD codes and this text to identify death certificates on which S. aureus and MRSA was mentioned.

The Tenth Revision of ICD (ICD-10) has been used to code deaths in England and Wales since 2001. The ICD-10 codes used to select deaths in order to then search manually are identified in Box 1 and Box 2 below. Initially, all deaths were extracted that had a code which specifically related to Staphylococcus or S. aureus infection mentioned on the death certificate. The codes used to identify these deaths are given in Box 1. In addition, all deaths which had non-specific codes (one which could include a Staphylococcal or S. aureus infection but could also include other infections) mentioned on the death certificate were extracted. The codes used to identify these deaths are given in Box 2. The text of these death certificates was then searched manually to identify S. aureus and MRSA.

Deaths with an underlying cause of S. aureus were identified by selecting those deaths with a mention of S. aureus that also had as the underlying cause one of the causes of death listed in Box 1 or Box 2. The same procedure was followed for the identification of those deaths with MRSA as the underlying cause. As in previous MRSA reports (Office for National Statistics 2010a) where MRSA was mentioned on the death certificate, the code A41.9 (septicaemia, unspecified) was taken to indicate that MRSA was also the underlying cause of death. This is because this code is sometimes selected as the underlying cause of death when MRSA septicaemia is mentioned on the death certificate.

Since 1986, ONS has used the internationally recommended death certificate for neonatal deaths (infants aged under 28 days). This means that these deaths cannot be assigned an underlying cause of death. However, as the data were based on deaths where S. aureus and MRSA were mentioned on the death certificate, neonates have been included. Neonatal deaths were extracted in the same way as described above for post-neonatal deaths.

Background notes

1. The number of deaths due to MRSA is difficult to estimate. Trends in mortality are usually monitored using the underlying cause of death (the disease which initiated the train of events leading directly to death). However, MRSA (and other healthcare associated infections) are often not the underlying cause of death. Those who die with MRSA are usually patients who were already very ill, and it is their existing illness, rather than MRSA, which is often designated as the underlying cause of death. There is therefore an interest in the number of deaths where MRSA contributed to the death - only conditions which contribute directly to the death should be recorded on the death certificate. Results presented in this bulletin identify deaths where the underlying cause was MRSA and also where MRSA was mentioned as the underlying cause or as a contributory factor in the death.
   

2. Although MRSA is commonly referred to as a healthcare associated infection, it is not possible to state from the information on a death certificate where the infection was acquired, nor can assumptions be made about quality of care. People are often transferred between hospitals, care homes and other establishments, and may acquire infections in a different place from where they died.
   
   
3. Guidance on death certification, with specific reference to healthcare associated infections, was issued to doctors in May 2005 (revised in 2010) (Office for National Statistics 2010b). This was followed by a message from the Chief Medical Officer to all doctors reminding them of their responsibilities with respect to death certification and drawing their attention to the guidance (Department of Health 2005).
   
   
4. There are two types of rates reported in this bulletin; age-specific and age-standardised. Age-specific (also known as 'crude') rates may be calculated for given age groups and are defined as the number of deaths in the age group per million (or thousand) population in the same age group. They do not allow comparison between populations which may contain different proportions of people of different ages. Age-standardised (also known as directly-standardised) rates make allowances for differences in the age structure of the population, over time and between sexes. The age-standardised rate for a particular disease is that which would have occurred if the observed age-specific rates for the disease had applied in a given standard population. In this bulletin, the European standard population has been used. This is a hypothetical population standard, which is the same for both males and females, allowing standardised rates to be compared over time and between sexes.
   
   
5. Rates were not calculated where there were fewer than three deaths in a cell, denoted by ':'. It is ONS practice not to calculate rates where there are fewer than three deaths in a cell, as rates based on such low numbers are susceptible to inaccurate interpretation. Rates which were calculated from less than 20 deaths are distinguished by italic type as a warning to the user that their reliability as a measure may be affected by the small number of events.
   
   
6. Within this bulletin, a difference which is described as 'statistically significant' has been assessed using confidence intervals. Confidence intervals are a measure of the statistical precision of an estimate and show the range of uncertainty around the estimated figure. Calculations based on small numbers of events are often subject to random fluctuations. As a general rule, if the confidence interval around one figure overlaps with the interval around another, we cannot say with certainty that there is more than a chance difference between the two figures.
   
   
7. Special extracts and tabulations of deaths involving C. difficile data for England and Wales are available to order for a charge (subject to legal frameworks, disclosure control, resources and agreement of costs, where appropriate). Such requests or enquiries should be made to:
    
   Mortality Analysis Team, Health and Life Events Division
   Office for National Statistics
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   Tel: 01633 456736
   Email: mortality@ons.gsi.gov.uk
   
   
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9. Besides ONS staff, the following persons are given 24-hour pre-release access to this bulletin:
   
   

   Pre-release access

   Position	Organisation
   Secretary of State for Health	Department of Health
   Private Secretary to Secretary of State for Health	Department of Health
   Special Adviser to Secretary of State for Health	Department of Health
   Minister of State for Health	Department of Health
   Assistant Private Secretary to Minister of State for Health	Department of Health
   National Director, Health Care Associated Infections	Department of Health
   Health Care Associated Infections Policy Team Leader	Department of Health
   Statistician	Department of Health
   Senior Press Officer	Department of Health
   Press Officer	Department of Health
   Chief Medical Officer	Welsh Government
   Statistician	Welsh Government

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10. Details of the policy governing the release of new data are available from the Media Relations Office.
    
    
11. National Statistics are produced to high professional standards set out in the Code of Practice for Official Statistics. They undergo regular quality assurance reviews to ensure that they meet customer needs. They are produced free from any political interference.
    
    

12. References

    Department of Health (2003) Winning Ways: Working together to reduce Healthcare Associated Infection in England: Report of the Chief Medical Officer, accessed 9 August 2011
    
    Department of Health (2005) CMO Update, Issue 42, Summer 2005, accessed 9 August 2011
    
    Department of Health (2007) A simple guide to MRSA, accessed 9 August 2011, available at:

    Department of Health (2010) The Operating Framework for the NHS in England 2011/12, accessed 9 August 2011
    
    Health Protection Agency (2011a) Staphylococcus aureus, accessed 9 August 2011

    Health Protection Agency (2011b) Mandatory Surveillance of Staphylococcus aureus bacteraemia, accessed 9 August 2011
    
    Office for National Statistics (2010a) Deaths involving MRSA: England and Wales, 2009, accessed 9 August 2011
    
    Office for National Statistics (2010b) Guidance for doctors completing Medical Certificates of Cause of Death in England and Wales, accessed 9 August 2011, available on the General Register Office website
    
    Public Health Wales (2011) All Wales infection surveillance reports, accessed 9 August 2011

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