Healthcare-associated infections

We analyse changes in annual counts of healthcare-associated infections, as well as weekly numbers of acute respiratory infection outbreaks in hospitals and care homes.



Last updated: 17/08/2023


Healthcare-associated infections (HCAIs) are infections that patients get while receiving medical or surgical treatment, or from being in contact with healthcare services. The most well-known HCAIs include methicillin-resistant Staphylococcus aureus (MRSA) and Clostridioides difficile (C. difficile). The emergence of new infections can pose a significant risk, as highlighted by the transmission of Covid-19 in health and care settings during the pandemic. As a result, infection prevention and control is a key priority for the NHS.

The NHS has set targets related to these infections for many years, and has achieved reductions in the rates of these bloodstream infections. But rates of other bacterial infections, including E. coli, Klebsiella and Pseudomonas, have been rising and the latest NHS Standard Contract has set new thresholds for Trusts and CCGs to reduce these infections.

Respiratory infection outbreaks

An acute respiratory infection outbreak is defined by the UKHSA as two or more laboratory confirmed cases of Covid-19, influenza or another respiratory pathogen linked to a particular setting. In care homes and hospitals, acute respiratory infection outbreaks generally peak in winter; in winter 2019-20 there was a peak of 82 new outbreaks in care homes in week 1 of 2020 (beginning 30 December 2019) and a peak of 13 new outbreaks in hospitals in week 2 of 2020 (beginning 6 January 2020).

In March 2020, the number of new outbreaks increased dramatically, driven by the Covid-19 pandemic. New outbreaks in care homes increased from 17 in week 10 (beginning 2 March 2020) to 1,010 in week 15 (beginning 6 April 2020). In hospitals there was a peak of 52 new outbreaks in week 14 (beginning 30 March 2020). Outbreaks fell during the summer of 2020, and since then there have been further peaks happening alongside subsequent waves of Covid-19.

The winter of 2021-22 saw high peaks in acute respiratory infection outbreaks; 1,080 outbreaks in care homes and 94 outbreaks in hospitals occurred in the last two weeks of 2021. Since then, in 2022, although outbreaks peaked every couple of months, they were not as large as they were in 2020 and 2021. In the summer of 2023, the number of outbreaks in both settings have gradually declined, resulting in 3 care home and 0 hospital acute respiratory infection outbreaks in early July (week 26) of 2023. 

It is worth noting that the data presented here does not indicate the number of individuals infected in each outbreak, nor does it tell us about the disease severity caused by the outbreak. No data was published between 20 May 2019 and 29 September 2019, resulting in a break in the time series.


Escherichia coli infections

Enhanced surveillance of E. coli bacteria has been mandatory for NHS acute trusts since June 2011. Following a worrying increase in E.coli infections, the NHS Patient Safety Strategy included a goal to decrease healthcare-associated Gram-negative bloodstream infections by 25% by 2021 and halve them by 2024. E. coli represents 55% of all Gram-negative bloodstream infections, making the reduction of the number of E. coli infections an important safety issue. Preventing bloodstream infections would also reduce the need to prescribe antimicrobials – a key way to mitigate antibiotic resistance.

Between 2012/13 and 2019/20, the total number of E. coli infections increased by 34%, from 32,309 to 43,294. The number of community-onset cases increased by 44%, but the number of hospital-onset cases only increased by 4%. The smaller increase is likely to reflect higher rates of blood culture testing with increased awareness of sepsis risk. In 2020/21, the total number of E. coli infections decreased by 15%, possibly due to interventions and changes in healthcare practices due to the Covid-19 pandemic. In 2021/22, 37,965 E.coli infections were reported, of which around 80% emerged in the community. 

Klebsiella and Pseudomonas infections 

Following E.coli, Klebsiella and pseudomonas aeruginosa are the most common causes of gram-negative infections. Between 2017/18 and 2021/22, annual counts of Klebsiella increased by 17% from 9,782 to 11,409. Meanwhile, the total number of Pseudomonas cases remained steady at around 4,300 cases per year. Trends in data for the two most recent years should be interpreted with caution as it is unclear whether they have occurred due to the Covid-19 pandemic or represent a change in the prevalence of these bacteraemia in England.

C. difficile infections

In 2007, the levels of healthcare-associated infections, including C. difficile, became a major national concern, in particular following the Healthcare Commission’s investigation into Maidstone and Tunbridge Wells NHS Trust. Action to address these problems was far-reaching and included new legislation as well as focused investment, regulation, and performance monitoring against targets. Following this focus in 2007, the total number of C. difficile infections decreased year-on-year to reach a low of 13,362 cases in 2013/14. 

In 2014/15 there was a slight increase in C. difficile infections from the previous year, a 4% increase for hospital-onset cases and an 8% increase for community-onset cases. Since then, the number of C. difficile infections has fluctuated minimally over time. In 2021/22, there were 5,344 hospital-onset cases and 8,905 community-onset cases.

About this data

National flu and Covid-19 surveillance reports

Acute respiratory infection incidents are based on situations reported to Public Health England Health Protection Teams. A confirmed outbreak of acute respiratory infections is defined as two or more laboratory confirmed cases (Covid-19, influenza or other respiratory pathogens) linked to a particular setting.

C. difficile and E. coli data

The bacterial infections are deemed to be hospital-onset if the following rules are met:

  • the location where the specimen was taken is given as 'acute trust' or is not known;
  • the patient was either an 'In-patient', 'Day-patient', in 'Emergency assessment' or the patient type is not known;
  • the patient's specimen date is on, or after, the third day of the admission (for MRSA and E. coli) or the fourth day of the admission (for C. difficile), where the day of admission is day one.

If the above rules are not met, then cases are deemed to be community-onset.