Deaths involving MRSA: 2008 to 2012

• The number of death certificates mentioning Meticillin-resistant Staphylococcus aureus (MRSA) fell by 20% from 364 in 2011 to 292 in 2012

• Of the 292 death certificates mentioning MSRA, 38 (13%) also identified this organism as the underlying cause of death

• MRSA death rates have consistently fallen in recent years. The latest figures show that rates decreased by 79% in males and 76% in females between 2008 and 2012

• In the period 2008–12, MRSA death rates increased with age and were higher for males than for females

• In the period 2008–12, MRSA was involved in 0.1% of all deaths and 0.2% of all hospital deaths

Meticillin-resistant Staphylococcus aureus (MRSA) is a type of Staphylococcus bacteria that is resistant to antibiotics known as beta-lactams. Staphylococcus aureus (S. aureus) bacteria can cause mild to life threatening disease if there is an opportunity for it to enter the body through broken skin or a procedure requiring the use of an invasive medical device.

This bulletin presents the latest figures for deaths where MRSA was mentioned or was identified as the underlying cause of death on death certificates. Figures are presented for England and Wales by sex, age group and place of death. Comparisons are made between data for 2012, the latest year, and previously published data from 1993 onwards. Information is given about the context and use of the statistics, and the methods used to produce them.

Figures are based on deaths registered in each calendar year rather than those occurring in each year. Since the majority of deaths involving MRSA registered in 2012 also occurred in the same year, registration delays are likely to have no impact on the findings in this bulletin. Please see the section on registration delays for further information.

ONS recently revised mid-2002 to 2010 population estimates in light of the 2011 Census. MRSA death rates relating to this period have therefore been revised and may differ from previously published figures.

S. aureus is a common type of bacteria (germ) found on the skin and in the nostrils of about a third of healthy people without it causing any harm to them (HPA, 2010).

It can cause disease if there is an opportunity for it to enter the body through broken skin or a procedure requiring the use of an invasive medical device (HPA, 2013). If the bacteria enter the body, mild to life-threatening illnesses may then develop. These include skin and wound infections, infected eczema, abscesses or joint infections and pneumonia. It also has the potential to induce infection of the bone (osteomyelitis), infections of the heart valves (endocarditis) and bacteraemia (blood stream infection), leading to infections in any of the major organs of the body (HPA, 2013; WHO, 2013). S. aureus is also responsible for many serious community- and hospital- acquired infections, being the most frequently isolated bacterial pathogen from patients with hospital-acquired infections, especially those with implants or prosthetic devices (WHO, 2013).

Most strains of S. aureus are sensitive to the more commonly used antibiotics, and infections caused by them can be effectively treated. However, some have developed resistance to these antibiotics and often require different types of antibiotics to treat them. MRSA is a type of S. aureus bacteria that is resistant to antibiotics known as beta-lactams. This group of antibiotics include meticillin and other more common antibiotics such as oxacillin, penicillin and amoxicillin (CDC, 2010).

The concern about MRSA is in part due to the fact that it shows a higher degree of drug resistance than other types of S. aureus and also because it has become particularly associated with hospital acquired infections (Public Health Wales, 2011). There is also growing concern about community-acquired MRSA in some parts of the world, with studies (Herold et al. 1998; Salmenlinna S, Lyytikäinen O and Vuopio-Varkila J, 2002) suggesting that this type of MRSA can be found in otherwise healthy people with no previous contact with healthcare facilities or hospitalised persons.

Incidence and mortality data for S. aureus and MRSA infections in England and Wales are used by various organisations, including the Department of Health (DH), Health Protection Agency (HPA), and Public Health Wales to highlight the burden of MRSA and to monitor and evaluate intervention programs aimed at reducing this burden. They are also used by local health boards (LHBs) and individual healthcare establishments.

In England, the Operating Framework for the NHS is the document which sets out the planning, performance and financial requirements for NHS organisations and the basis on which they will be held to account.

To reflect the NHS’s increased focus on controlling healthcare associated infections, the NHS Outcomes Framework 2013/14 (DH, 2012) highlights, ‘Treating and caring for people in a safe environment and protecting them from avoidable deaths,’ as one of the domains against which performance is assessed. One of the improvement areas identified as being important in achieving this goal is the reduction in the incidence of MRSA.

Of particular interest is the reduction of MRSA bloodstream infections as these are more common in healthcare settings and are more likely to be associated with undesirable outcomes. In 2001, the HPA developed a mandatory MRSA surveillance scheme on behalf of the DH to monitor trends and enable epidemiological analyses of MRSA bloodstream infections data.

Data gathered from the surveillance scheme has shown that there have been large reductions in the reports of MRSA bloodstream infections in recent years. For example, in 2012 there were 934 MRSA bloodstream infection reports made; a 21% reduction on the previous year at 1,187 (PHE, 2013).

In Wales, surveillance of MRSA bloodstream infections is managed by the Welsh Healthcare Associated Infection Programme (WHAIP), part of Public Health Wales. In recent years there has been a decrease in the number of cases in Wales. For example, the number of MRSA bloodstream infections fell by 11% from 229 in 2010 to 203 in 2011. Similarly the number of S. aureus bloodstream infection cases fell by 3% from 893 to 864 over the same periods (Public Health Wales, 2013).

Deaths involving S. aureus and MRSA statistics have been produced by the Office for National Statistics (ONS) for each year since 1993. Figures for recent years show a large decrease in the number and age-standardised rate of deaths where S. aureus and MRSA were the underlying cause of death or were mentioned anywhere on the death certificate. This trend is consistent with the decreases in incidence as reported by the HPA and Public Health Wales. The decreases may in part be due to interventions which are targeted at improving hospital-based infection control practices. It is however noteworthy that the English and Welsh surveillance reports only focus on bloodstream infections and not other types of infections associated with MSRA. Conversely, the figures presented in this report are for deaths from all MRSA related infections.

Results in this bulletin are presented for England and Wales combined while the downloadable reference tables also show results for both countries separately. Tables within the bulletin contain data for the latest five-year period for ease of presentation. However, time trends are examined from 1993 onwards.

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

In 2012, the number of death certificates mentioning S. aureus (including those resistant to meticillin) was 557, a 13% decrease on the previous year at 638. Although the number of deaths has fallen in recent years (see table 1), longer time trends show that there was an initial increase until 2006 when the numbers were five times those in 1993 when records began.

A similar trend was observed with MRSA, with the number of deaths decreasing in each year since peaking in 2006. The latest figures show that there were 292 mentions of MRSA on death certificates, a 20% decrease on the previous year at 364 deaths.

In 1993, MRSA accounted for 12% of all S. aureus mentions. Over time this proportion has fluctuated substantially, peaking at 82% in 2008. In 2012, MRSA accounted for 52% of the 557 deaths involving S. aureus.

While S. aureus and MRSA infections might contribute to a death, there are instances where they are also directly responsible for causing it. In 1993, of the 430 death certificates mentioning S. aureus, 36% also attributed the underlying cause of death to this germ. For MRSA, the figure was lower at 29%. By 2012, the percentage of S. aureus and MRSA mentions where these germs were also recorded as the underlying cause of death had fallen to 21% and 13% respectively.

Age-specific mortality rate for deaths mentioning S. aureus and MRSA

In each year, the number of death certificates mentioning S. aureus and MRSA, broken down by age and sex is small and therefore subject to random variation. To minimise the effect of this variation on the sex and age-specific rates, data from a five year period (2008 to 2012) were pooled to ensure robust conclusions could be drawn.

In the period 2008–12, the rate for deaths mentioning S. aureus and MRSA increased with age and was higher for males than for females.

For males, the rate for S. aureus was lowest among those under 45 years of age (1.8 deaths per million population) and highest among those aged 85 years and over (415.8 per million population). For females, the comparable figures for the two age groups stood at 1.4 per million population and 200.4 per million population respectively.

The rates for MRSA mentions were lower than those for S. aureus across all age groups. This is expected as MRSA is a subset of S. aureus and as such there are fewer deaths from it. Conversely, the relative difference between rates for those less than 45 years of age and those aged 85 years and over was notably greater for MRSA. This disparity suggests that compared with S. aureus, MRSA deaths were relatively more concentrated among those in the oldest age group.

In the period 2008–12, the MRSA rate for males aged 85 years and over was 574 times greater than the rate for males under 45 years of age (301.4 compared with 0.5 per million population). A similar pattern was observed for females; however, the relative difference between these two age groups was smaller than for males (see table 2).

Sick people in healthcare facilities are at increased risk of contracting MRSA. Older people are particularly vulnerable because they are likely to have relatively weaker immune systems compared with younger people and to have other underlying problems. The trends observed in age-specific MRSA death rates are therefore expected.

Age-standardised rates for deaths mentioning S. aureus and MRSA

For both sexes, there was a steady decline in the age-standardised rate for deaths mentioning S. aureus and MRSA between 2008 and 2012. This decline tends to mask the substantial variation in rates between 1993 and 2012. This period was characterised by an initial increase in rates in each year up to 2006, when they peaked, before falling to date. Nevertheless, it is noteworthy that for the second year running, the latest death rate for S. aureus was not significantly different from the rate in 1993 when records began.

In 2012, the rates for deaths mentioning S. aureus were 8.3 and 4.4 deaths per million population for males and females respectively. For MRSA, the comparable figures were 3.9 per million population for males and 2.4 per million population for females. As with S. aureus there has been a steady decline in death rates in recent years; however, the most recent rates are still significantly higher than those observed in 1993.

In the period 2008–12, deaths involving S. aureus accounted for 0.3% and MRSA 0.1% of all deaths registered in England and Wales.

A breakdown by place of death shows that 90% of deaths involving S. aureus and 87% of MRSA deaths occurred in NHS hospitals across England and Wales. These figures represent 0.3% and 0.2% of all deaths in NHS hospitals respectively.

As the majority of deaths in England and Wales occur in NHS hospitals, it is expected that the proportions of deaths involving S. aureus and MRSA in these establishments would be higher than those in other establishment types. In general, care homes had the second highest number and percentage of all deaths involving S. aureus and MRSA, with the majority of these deaths occurring in care homes not administered by local authorities.

An estimated 6% of S. aureus and 9% of MRSA deaths occurred in non-local authority care homes. In this establishment type, S. aureus and MRSA each accounted for 0.1% of deaths from all causes. Compared with these figures, the number and percentage of deaths involving S. aureus and MRSA in local authority care homes were substantially lower (see reference table 1 in the reference tables section).

Data source

The information used in this bulletin is based on the details collected when deaths are certified and registered. All deaths are coded by ONS according to the International Classification of Diseases (ICD) produced 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 related to causes identified on the death certificate. The Tenth Revision of ICD (ICD-10) has been used to code deaths in England and Wales since 2001.

Approach used in selecting deaths

The text on death certificates were used in combination with ICD-10 codes to identify those mentioning S. aureus and MRSA in a two step process.

A number of infections are specifically related to S. aureus or other staphylococcal species. First, all deaths were extracted where any of these infections was mentioned on the death certificates. These deaths were extracted using the ICD-10 codes given in Box 1 in reference table 2. The text of these death certificates was then searched, both electronically and manually, to identify S. aureus and MRSA.

Conversely, some infections have different causative organisms and may be caused by Staphylococcus species or other pathogens. The second step therefore involved extracting all deaths which had these non-specific infections mentioned on the death certificate. The codes used to identify these infections are given in Box 2 (see reference table 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 infections listed in Box 1 or Box 2. The same procedure was followed in order to identify deaths with MRSA as the underlying cause.

Since 1986, ONS has used the internationally recommended death certificate for neonatal deaths (infants under 28 days old). This certificate was only designed to record all conditions found at death. This means that neonates 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.

Registration delays

The information used to produce mortality statistics is based on the details collected when deaths are certified and registered. In England and Wales, deaths should be registered within five days of the death occurring, but there are some situations which result in the registration of the death being delayed. Deaths considered unexpected, accidental or suspicious will be referred to a coroner who may order a post mortem or carry out a full inquest to ascertain the reasons for the death.

Statistics on deaths involving MRSA and S. aureus are presented based on the number of deaths registered in each calendar year, rather than the number of deaths that actually occurred in that year. This method is used because there is a requirement for consistent and timely data, despite a potential limitation in data quality caused by registration delays.

On average, the median registration period for deaths mentioning MRSA and where this organism was identified as the underlying cause of death was three and four days respectively in 2012. The majority of deaths mentioning MRSA and those identifying it as the underlying cause were registered within one month (88% and 97% respectively). Conversely, 8% and 3%, respectively, were delayed by six months or more. In 2012, approximately 89% (259 out of 292) of registered deaths mentioning MRSA also occurred in the same year. Of the 38 deaths registered in 2012 where MRSA was the underlying cause of death, 36 (95%) also occurred in the same year.

Since the majority of deaths involving MRSA registered in 2012 also occurred in the same year, registration delays are likely to have no impact on the findings in this bulletin.

Figures for deaths involving S. aureus and MRSA can be found in reference tables on the ONS website. The content of each table is further described below:

• Reference table 1 - Deaths involving S. aureus and MRSA by place of death, 2008–12

• Reference table 2 - Age-standardised rates for deaths involving Staphylococcus aureus and MRSA, and the number of deaths by annual registration quarter, England and Wales, 1993–2012

• Reference table 3 - Deaths involving S. aureus and MRSA by country, sex and five-year age group, 1993–2012