30 day all-cause mortality following MRSA, MSSA and Gram-negative bacteraemia and C. difficile infections: 2021 to ...

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Updated 9 November 2023

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Main findings

When examining mortality rates over the surveillance periods, there has been:

a substantial decline in the mortality rate of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia and Clostridioides difficile infections (CDI), especially for hospital-onset (HO) cases, since the start of surveillance in April 2007
a particularly evident improvement in the mortality rate for MRSA and CDI before 2015 that was coupled with a decrease in incidence of these infections
a slowly increasing trend in the mortality rate of methicillin-susceptible Staphylococcus aureus (MSSA) bacteraemia since April 2011, primarily driven by an increase in the mortality rate of community-onset (CO) cases, with a sharper increase in mortality rate and CFR of all cases in the most recent 2 financial years
a slowly increasing trend in the mortality of CO Escherichia coli (E. coli) bacteraemia between April 2012 and March 2020, which has since reversed; the mortality rate of HO cases has, on the other hand, been stationary since April 2012
since surveillance started in April 2017 for Klebsiella species (Klebsiella spp.) bacteraemia, the mortality rate for CO cases has been relatively stationary, whilst the mortality rate for HO cases has decreased after the large 2020 increase
a decrease in the mortality rate for Pseudomonas aeruginosa (P. aeruginosa) bacteraemia between financial years April 2017 to March 2018 and 2018 to 2020, but a peak in financial year 2020 to 2021; a subsequent decline in the most recent financial year was observed

This report presents data on the 30 day all-cause mortality following MRSA, MSSA, E. coli, P. aeruginosa, Klebsiella spp. bacteraemia and Clostridium difficile (C. difficile) infection.

All data tables associated with this report are available in the accompanying dataset for 2021 to 2022. Data in this report are presented as 30 day all-cause mortality rate and case fatality rates (CFRs).

Mortality rate is a widely used outcome for assessing risk of death. Mortality rate is the number of deaths divided by the population at risk. This reflects the incidence of all-cause deaths following these infections in the population.

Case fatality rate (CFR) is the number of deaths as a percentage of all reported cases. This provides a measure for comparing survivability of different infections.

This report presents data on all-cause mortality, and therefore includes deaths that may not be directly attributable to the infections.

Between the financial year April 2020 to March 2021 and April 2021 to March 2022, the CFR slightly decreased for all collections:

E. coli bacteraemia from 16.0% to 15.0%
Klebsiella spp. bacteraemia from 21.8% to 19.5%
MSSA bacteraemia from 23.7% to 22.1%
MRSA bacteraemia from 28.2% to 26.3%
P. aeruginosa bacteraemia from 27.7% to 25.0%
C. difficile infection from 14.9% to 13.7%

These reductions were primarily driven by a more substantial change in the CFR among HO cases (in particular, from 33.9% to 27.0% for P. aeruginosa bacteraemia and from 34.3% to 29.3% for MRSA bacteraemia).

Comparing across financial years April 2020 to March 2021 and April 2021 to March 2022, the mortality rate (expressed in deaths per 100,000 population per financial year) slightly decreased for:

E. coli bacteraemia from 10.2 to 9.8
Klebsiella spp. bacteraemia from 4.2 to 3.8
P. aeruginosa bacteraemia from 2.0 to 1.9
MSSA bacteraemia from 4.8 to 4.7

These improvements go against the increase seen in the previous 2 financial years. The mortality rate remained stable for MRSA bacteraemia (0.3), but it marginally increased for C. difficile infection (3.2 to 3.4); this is an ongoing trend that is reflective of an increasing incidence of CDI.

Between March 2020 and March 2022, England experienced 3 major waves of coronavirus (COVID-19) infection. During the early part of the pandemic, many elective procedures in hospitals were cancelled, leading to reduced hospital activity. During this decline in hospital activity, reductions were also observed in the number of Gram-negative and Staphylococcus aureus (S. aureus) bacteraemia, and CDI reported during this period.

A small increase in CFR was observed across all organisms in the first year of the COVID-19 pandemic followed by a decrease in the most recent year. It is unclear how much of the increase in CFR during the first pandemic year could be attributed to COVID-19 but 21% of CDI cases had a positive COVID-19 test in the 4 weeks before or after CDI positive sample at this time, as described in the previous edition of this report, covering 2020 to 2021.

Results for all mandatory surveillance infections

Data throughout this report are presented in financial years, with the years starting in April and ending in March. Hereafter, the month names will be omitted for brevity purposes, such that the most recent financial year will be described as 2021 to 2022, rather than April 2021 to March 2022.

During financial year 2021 to 2022, there were a total of 80,913 cases of E. coli, Klebsiella spp., P. aeruginosa, MRSA and MSSA bacteraemia, and CDI in England, 78,956 (97.6%) cases could be linked to NHS Spine data. This was an increase from the previous year's total cases of 77,150 (financial year 2020 to 2021).

There were 13,501 deaths within 30 days of taking a specimen (blood culture for bacteraemia, faecal sample for CDI). The highest number of these deaths were associated with E. coli at 5,549 deaths. This is 41.1% of deaths covered by this report. The overall mortality rate was 23.9 deaths per 100,000 population, with a CFR of 17.1% (Table S1 of the supplementary dataset and Figure 1).

The number of deaths has decreased from financial year 2020 to 2021 (13,984 deaths) to the current financial year 2021 to 2022 (13,501 deaths). The mortality rate and CFR have decreased by 0.8 deaths per 100,000 population and 1.5%, respectively.

Figure 1. Thirty-day all-cause case fatality rate by infection, England, financial year 2007 to 2008 to financial year 2021 to 2022

Escherichia coli bacteraemia

During financial year 2021 to 2022, 37,965 E. coli bacteraemia cases were reported in England. Information on mortality was available for 97.6% (37,043) of these cases (Table S2 of the supplementary dataset). There were 5,549 deaths within 30 days of an E. coli bacteraemia diagnosis, indicating a mortality rate of 9.8 deaths per 100,000 population and a CFR of 15.0%.

There was a declining trend in CFR starting from 16.8% during financial year 2012 to 2013 to 13.9% during financial year 2018 to 2019, after which the CFR then increased to 16.0% by financial year 2020 to 2021. The mortality rate increased between financial years 2012 to 2013 and 2021 to 2022 from 9.7 to 9.8 deaths per 100,000 population. Mortality rate peaked at 10.7 during financial year 2019 to 2020 but has subsequently declined in the most recent 2 financial years.

Variation by onset of bacteraemia

The surveillance of CO mortality rate peaked during financial year 2019 to 2020 at 7.7 deaths per 100,000 population. This has subsequently decreased to 7.1 (Table S3 of the supplementary dataset and Figure 2). The mortality rate of HO cases increased to 4.8 deaths per 100,000 bed-days during financial year 2019 to 2020 and 5.3 deaths per 100,000 bed-days during financial year 2020 to 2021, coinciding with the COVID-19 pandemic. The mortality rate subsequently decreased in the financial year 2021 to 2022 to 4.7 deaths per 100,000 bed-days (Table S3 of the supplementary dataset and Figure 3).

The CFR of HO cases declined from 23.6% to 22.6% in between financial years 2012 to 2013 and 2021 to 2022. CO cases also declined from 14.8% to 13.3% over the same period (Table S3 of the supplementary dataset and Figure 4). The CFR in HO and CO cases have decreased between financial year 2012 to 2013 and 2021 to 2022, although the decrease was only constant between financial years 2012 to 2013 and 2019 to 2020, which coincides with the start of the COVID-19 pandemic. There was an increase of 2% in CFR of CO cases between financial years 2019 to 2020 and 2020 to 2021 (12.6% to 14.6%). The current financial year (2021 to 2022) then saw a decline in CFR of CO cases to 13.3%.

Figure 2. Thirty-day all-cause mortality rate of community onset E. coli bacteraemia, England, financial year April 2012 to March 2013 to financial year April 2021 to March 2022

Figure 3. Thirty-day all-cause mortality rate of hospital onset E. coli bacteraemia, England, financial year April 2012 to March 2013 to financial year April 2021 to March 2022

Figure 4. Thirty-day all-cause case fatality rate of E. coli bacteraemia by onset, England, financial year April 2012 to March 2013 to financial year April 2021 to March 2022

Variation by NHS commissioning region

During financial year 2021 to 2022, regional mortality rate ranged from 7.7 deaths per 100,000 population in London to 12.4 deaths per 100,000 population in the North East and Yorkshire. Over the same period, CFRs ranged from 13.5% in London to 16.1% in the North East and Yorkshire (Table S4 of the supplementary dataset).

Variation by age and sex

Mortality rate and CFR generally increased with age and was greater in male patients than female patients. The exception to this was patients aged under 1 year where mortality rate and CFR was higher compared with those aged 1 to 14 years (Table S5 of the supplementary dataset, Figure 5 and Figure 6).

During financial year 2021 to 2022, among male patients, the highest mortality rates were in those aged over 85 years (175.6 deaths per 100,000 population) and those aged 75 to 84 years (64.1 per 100,000 population). This equated to CFRs of 22.3% and 17.3% respectively. The CFRs for these groups both decreased from financial year 2020 to 2021 and the mortality rate for those aged 75 to 84 years decreased by 2.4 deaths per 100,000 population. However, the mortality rate for those aged 85 years and over increased by 0.8 deaths per 100,000 population.

Mortality rate in males declined between financial years 2020 to 2021 and 2021 to 2022 in all age groups except for those aged 1 to 14 years. However, numbers of deaths are very small in this age group so differences should be interpreted with caution.

The highest mortality rates among female patients during the financial year 2021 to 2022 were seen in those aged over 85 years at 92.7 per 100,000 population and in those aged 75 to 84 years at 38.2. This equates to a CFR of 18.8% and 14.4% of cases respectively. The mortality rate and CFR in those aged under 1 year increased from financial year 2020 to 2021, with mortality rates for females increasing from 5.5 to 5.8 per 100,000 population and CFR increasing from 7.8% to 8.9% of cases.

Mortality rates and CFRs also increased in females aged 1 to 14 years and 15 to 44 years, although numbers of deaths are small in these groups so differences should be interpreted with caution.

Figure 5. Thirty-day all-cause mortality rate of E. coli bacteraemia by age and sex, financial year April 2012 to March 2013 versus financial year April 2021 to March 2022, England

Figure 6. Thirty-day all-cause case fatality rate of E. coli bacteraemia by age and sex, financial year April 2012 to March 2013 versus financial year April 2021 to March 2022, England

Klebsiella species bacteraemia

During financial year 2021 to 2022, 11,409 Klebsiella spp. bacteraemia cases were reported in England. Information on mortality was available for 97.1% (11,078) of these cases (Table S6 of the supplementary dataset). There were 2,162 deaths within 30 days of a Klebsiella spp. Bacteraemia diagnosis giving a mortality rate of 3.8 deaths per 100,000 population. The CFR was 19.5%.

Mandatory surveillance of Klebsiella spp. bacteraemia started during financial year 2017 to 2018, meaning trends are not as established as those in data collections such as MRSA or E. coli bacteraemia. The mortality rate increased from 3.4 to 3.8 deaths per 100,000 population between financial years 2017 to 2018 and 2021 to 2022. Conversely, the CFR decreased from 20.2% (1,896 deaths) to 19.5% (2,162 deaths) in between financial years 2017 to 2018 and 2021 to 2022.

A large increase in CFR was observed between financial years 2018 to 2019 and 2020 to 2021, coinciding with the COVID-19 pandemic. The CFR increased from 18.7% to 21.8% in between financial years 2018 to 2019 and 2020 to 2021. The mortality rate also increased from 3.5 per 100,000 population between financial year 2018 to 2019 to 4.2 per 100,000 population during financial year 2020 to 2021.