Deaths involving MRSA in Wales: 2014

• There were 25 death certificates mentioning Meticillin-resistant Staphylococcus aureus (MRSA) in 2014

• In 2014, approximately 1 in 6 death certificates (4 out of 25) mentioning MRSA also identified it as the underlying cause of death

• The age-standardised rate for deaths involving MRSA initially increased, from 5.7 to 40.2 deaths per million population, between 1994 and 2005, but has since fallen to a level similar to that observed in 1994. The rate in 2014 was 8.1 deaths per million

• The age-specific MRSA death rates increased with age and tended to be higher for males than females

• In the period 2010 to 2014, the majority of deaths involving MRSA occurred in NHS hospitals (93%). However, these deaths accounted for only 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. Therefore the MRSA figures presented here are a subset of the Staphylococcus aureus (S. aureus) figures. 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 Wales and are broken down by sex, age group and place of death. Comparisons are made between data for 2014, 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 2014 also occurred in the same year, registration delays are unlikely to affect our findings. Please see the section on registration delays for further information.

In 2014, there were 25 death certificates mentioning MRSA and 47 mentioning S. aureus (including those resistant to meticillin). The majority of these deaths were among males (60% of MRSA and 53% of S. aureus deaths respectively).

The number of MRSA deaths increased between 1993 and 2005, but has since decreased. The trend in our data from 2005 onwards is consistent with the trend in the incidence of MRSA bloodstream infections reported by the Welsh Healthcare Associated Infection Programme (WHAIP), part of Public Health Wales. The decreases may partly be due to interventions which are targeted at improving hospital-based infection control practices. However, unlike our figures, the incidence data collected by WHAIP only focuses on bloodstream infections and not other types of infections associated with MRSA.

In 1993, approximately 7% of S. aureus infections mentioned on death certificates were reported as meticillin-resistant (MRSA). The proportion of S.aureus deaths that is reported as meticillin-resistant tends to fluctuate annually. Nevertheless, there was a sharp increase in this proportion from 7% in 1993 to a peak of 89% in 2008. The proportion has since decreased to 53% in 2014, the lowest recorded since 1995.

MRSA and S. aureus infections may contribute to a death or directly cause it. Approximately 16% (4 out of 25) of death certificates mentioning MRSA also recorded it as the underlying cause of death, while 21% (10 out of 47) of those mentioning S. aureus recorded this organism as the underlying cause of death.

The age-standardised rates presented here are for all persons (males and females combined). This is because the number of deaths in each year since the 2005 peak has fallen to the extent that there are no longer sufficient deaths to calculate robust sex-specific age-standardised rates for individual years. We couldn’t calculate the MRSA death rate for 1993 because the number of deaths in that year weren’t sufficient to do so.

A ranking of the top 10 causes of serious bloodstream infections published by WHAIP showed that MRSA dropped from the fifth most common cause between October 2004 and November 2005, to ninth place in 2014. The 2014 rank reflects the dropping incidence of MRSA bloodstream infections in hospitals across Wales and is consistent with the trend in our MRSA death rates since 2005.

The age-standardised rate for deaths mentioning MRSA increased significantly between 1994 and 2005, before falling to a level similar to that observed in 1994. The rate increased from 5.7 per million population in 1994 to a peak of 40.2 per million in 2005. It has since fallen to 8.1 per million in 2014.

A similar trend was observed for deaths mentioning S. aureus, with the age-standardised rate initially increasing, from 11.1 to 49.7 per million population between 1993 and 2005, before falling to 15.4 per million in 2014.

Due to the small number of death certificates mentioning MRSA and S. aureus in each year, we have pooled data from 5-year periods in order to observe differences between the sexes and age groups.

In each 5-year period between 1993 to 1997 and 2010 to 2014, the age-specific rate for deaths mentioning MRSA and S. aureus increased with age and tended to be higher for males than females. For both sexes, rates were lowest among those under the age of 55 years and highest among those aged 85 years and over.

There was no significant change in the age-specific MRSA death rates for males and females under 55 years and females aged 55 to 64 years over time. In other age groups, rates initially increased before falling to levels similar to those observed in the period 1993 to 1997. For example, rates for males aged 55 to 64 years increased significantly, from 8.0 deaths per million in the period 1993 to 1997 to a peak of 31.9 per million in 2002 to 2006, before falling to 7.4 per million in 2010 to 2014.

In each period, a higher proportion of S. aureus deaths were MRSA in the oldest age group compared with the youngest. For example, among those aged 85 years and over in 2010 to 2014, approximately 79% of male and 63% of female S. aureus deaths were MRSA. Conversely, among those under 55 years in the same period years, 41% of male and 38% of female S. aureus deaths were MRSA.

Sick people in healthcare facilities are at increased risk of contracting MRSA. These figures highlight the greater vulnerability of older people as they are likely to have relatively weaker immune systems compared with younger people and to have a number of coexisting health problems.

Deaths involving S. aureus accounted for 0.2% and MRSA 0.1% of all deaths registered in Wales in the period 2010 to 2014.

A breakdown by place of death shows that 94% of deaths involving S. aureus and 93% of MRSA deaths in Wales occurred in NHS hospitals. These figures represent 0.3% and 0.2% of all deaths in NHS hospitals respectively.

As the majority of all deaths in 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.

Non-local authority care homes had the second highest number and percentage of all deaths involving S. aureus and MRSA. In addition, 9 out of the 10 S. aureus deaths in this establishment type were reported as meticillin-resistant. Conversely, there were no deaths involving S. aureus and MRSA in local authority care homes.

S. aureus is a common type of bacteria (germ) found on the skin and in the nostrils of healthy people without it causing any harm (Public Health England, 2014).

Most strains of S. aureus are sensitive to the more commonly used antibiotics and the infections they cause can be effectively treated. However, some strains are resistant to these antibiotics. Most strains of S. aureus first developed resistance to penicillin in the 1950s. In the late 50s, chemists developed an antibiotic called meticillin which was not destroyed by the penicillin-resistant bacteria. However, resistant strains began to appear soon after the introduction of meticillin and these strains spread rapidly during the 1990s.The term MRSA refers to S. aureus bacteria that are resistant to antibiotics known as beta-lactams. This group of antibiotics include meticillin and other more common antibiotics such as oxacillin, penicillin and amoxicillin.

MRSA can cause mild to life threatening conditions if there is an opportunity for it to enter the body through broken skin or a medical procedure requiring the use of an invasive medical device (Public Health England, 2014). These include skin and wound infections, infected eczema, abscesses or joint infections and pneumonia, infections of the heart valves (endocarditis), bacteraemia (blood stream infection) and food poisoning.

In the community, the majority of MRSA infections are skin infections while in healthcare settings MRSA causes life-threatening bloodstream infections, pneumonia and surgical site infections (Centre for Disease Control and Prevention, 2015).

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 Wales are primarily used by Public Health Wales to highlight the burden of MRSA and to monitor and evaluate intervention programs aimed at reducing this burden. These data are also used by local health boards and individual healthcare establishments.

In 2004, the Welsh Government published its strategy for reducing healthcare associated infections in hospitals in Wales. In addition, there is a comprehensive surveillance of MRSA bloodstream infections managed by WHAIP. The surveillance programme provides Health Boards with information about rates of various infections in their institutions, highlighting potential areas for investigation and action.

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 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 MRSA and S. aureus 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 the reference table (155.5 Kb Excel sheet) . The text of these death certificates was then searched, both electronically and manually, to identify MRSA and S. aureus.

Conversely, some infections have different causative organisms and may be caused by Staphylococcus species or other pathogens. The second step therefore involves 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 in the reference table. The text of these death certificates was then searched manually to identify MRSA and S. aureus.

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 MRSA and S. aureus were mentioned on the death certificate, neonates have been included. Neonatal deaths were extracted in the same way as described 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 Wales, deaths should be registered within 5 days of the death occurring, but there are situations where this isn’t possible. 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 occurred. 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.

In 2014, the average (median) number of days between date of death and death registration for deaths where MRSA was mentioned on the death certificate or selected as the underlying cause was 4 days. The majority of deaths where MRSA was mentioned on the death certificate (80%) and those caused by it (75%) were registered within 5 days. All deaths directly caused by MRSA and 92% of those mentioning it on death certificates were registered within 30 days.

The majority of deaths involving MRSA registered in 2014 (23 out of 25 or 92%) and all those reporting it as the underlying cause occurred in the same year. As a result, registration delays are likely to have no impact on the trends reported in this bulletin.

Figures for deaths involving MRSA and S. aureus from 1993 to 2014 are available in the reference table on our website. This excel workbook (155.5 Kb Excel sheet) contains the number of deaths in each year, age-standardised rates, age-specific rates and a breakdown by place of death.