Scottish Surveillance of Healthcare Associated Infection Programme (SSHAIP)

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SSHAIP

Weekly Report Articles

09 January 2013

Quarterly report on the surveillance of Clostridium difficile infection (CDI) in Scotland, July - September 2012

Please note CDI rates in this report have been updated due to a subsequent revision of the national figures of hospital activity.
Please go to http://www.hps.scot.nhs.uk/haiic/sshaip/publicationsdetail.aspx?id=50174 for the revised data.

Executive Summary

  • This report provides a summary of CDI data for July to September 2012 (Q3 2012) in Scotland. This includes data for CDI in patients aged =>65 years and 15-64 years.
  • In total, 369 new cases of CDI in patients aged =>65 years were reported to Health Protection Scotland (HPS) during this quarter. The overall incidence rate for Scotland was 31.9 cases per 100 000 total occupied bed days. This is a 4% increase from the previous quarter, and the second consecutive increase in incidence rates in this age group.
  • In total, 147 new cases of CDI in patients aged 15-64 years were reported to HPS during this quarter. The overall incidence rate for Scotland was 41.6 cases per 100 000 acute occupied bed days. This is a 21% increase from the previous quarter.
  • Despite increases in the incidence rates over the past two quarters, the year on year trend analysis comparing Q4 2010-Q3 2011 to Q4 2011-Q3 2012 shows a non-statistically significant decrease in the overall incidence rate for patients aged =>65 years of 5.4% (95% CI: -17.8% to 8.8%). In patients aged 15-64 years, there was a non-statistically significant increase of 0.7% (95% CI: -15.4% to 19.9%).
  • Ten NHS boards reported an increase in incidence rates this quarter in one or other age group. Further investigations carried out by the boards have not revealed any common links between cases. However, the increases may be partly explained by the emergence and increase of C. difficile ribotype 078 in Scottish hospitals, and there may be sub-optimal compliance with Standard Infection Control Precautions and Transmission Based Precautions.
  • There remains scope for reduction of incidence rates in both age groups through continued local monitoring, appropriate prescribing, and maintenance of infection prevention and control measures. NHS boards are reminded to follow the national Guidance on Prevention and Control of CDI in Healthcare Settings in Scotland.
  • A single isolate of a novel ribotype (C. difficile ribotype 244) has been identified in Scotland for the first time this quarter. Ribotype 244 has become predominant in Australia and has been associated with a significant increase in the incidence rates in Australia since July 2011. Ribotype 244 has only been isolated rarely in the rest of the UK. There are no known links between the Scottish ribotype 244 case and Australia.

1. Introduction

Clostridium difficile infection (CDI) is an important healthcare associated infection and is a major cause of morbidity and mortality. Major risk factors for CDI include old age and previous use of antibiotics. Disease ranges from mild self-limiting diarrhoea to severe diarrhoea, pseudomembranous colitis, toxic megacolon and death.

In Scotland, mandatory surveillance of CDI was introduced in 2006 and initially focused on the incidence of CDI in patients aged =>65 years (the age group most at risk). In April 2009, the programme was extended to include patients aged 15-64 years.

The programme is supported by a ribotyping service provided by the Scottish Salmonella, Shigella and Clostridium difficile Reference Laboratory (SSSCDRL). Mandatory surveillance of ribotypes falls into two categories: a) clinical surveillance: isolates associated with outbreaks and severe disease, and b) representative surveillance: isolates from a fixed proportion of all cases including mild, moderate and severe disease. Surveillance of severe cases/outbreaks began in November 2007, and representative surveillance in January 2009.

The national surveillance programme is retrospective (i.e., three months in arrears). It is important that NHS boards have their own local CDI surveillance systems to alert local teams to the need for possible action. This surveillance report does not replace local monitoring of CDI by NHS boards' infection control teams.

2. Methods

Data sources and reporting

Full details of the data source (including denominators, calculation of rates and statistical analyses) and the definitions used to generate this report are published on the HPS website and may also be accessed from: http://www.documents.hps.scot.nhs.uk/hai/sshaip/publications/cdi/2012/methods-caveats-q3.pdf.

From January 2012, the scaling factor used in reporting the quarterly incidence rates has changed to 'per 100 000 bed days' instead of the previously used 'per 1000 bed days'.
All previous published data can be accessed at: http://www.hps.scot.nhs.uk/haiic/sshaip/clostridiumdifficile.aspx?subjectid=79#ar.

The Protocol for the Scottish Surveillance Programme for Clostridium difficile Infection (version 3.0) is available from: http://www.hps.scot.nhs.uk/haiic/sshaip/guidelinedetail.aspx?id=40899.

The protocol for the Snapshot Programme (representative surveillance) is available from: http://www.hps.scot.nhs.uk/haiic/sshaip/guidelinedetail.aspx?id=46879.

Identification of outliers

Funnel plots are used to identify outliers. The NHS board level incidence rates are plotted on the funnel plots against the number of 100 000 bed days with the 95% confidence limits for the Scottish incidence rate. NHS board level incidence rates outside the 95% confidence limits are considered outliers.

Analysis of trends

Trend analysis of incidence rates is based upon the most recent two years of data.

3. Results


3.1 Surveillance data

CDI incidence in patients aged =>65 years

The total number of new cases identified in patients aged =>65 years during Q3 2012 was 369 (in the previous quarter there were 365 cases). This is an overall incidence rate of 31.9 per 100 000 total occupied bed days (hereafter 'total bed days'), a 4% increase from the previous quarter (30.8 per 100 000 total bed days).

Individual incidence rates by NHS board for this quarter compared with the previous quarter are shown in Figure 1 (mainland NHS boards) and Figure 2 (island NHS boards and NHS National Waiting Times Centre (NWTC)). The separation of mainland from smaller NHS boards is to reflect the smaller denominators from the island NHS boards and NHS NWTC that make a single graph difficult to interpret.

There was a statistically significant decrease in the incidence rates in NHS Greater Glasgow & Clyde. Incidence rates decreased substantially in NHS Highland but this was not statistically significant. Substantial increases in incidence rates occurred in NHS Borders, NHS Dumfries & Galloway, NHS Forth Valley and NHS Lanarkshire (Figure 1).

Incidence rates decreased in NHS Orkney and NWTC, while there was an increase in NHS Western Isles. Overall case numbers were low (Figure 2).

Figures 3 and 4 show that the rates per 100 000 population were in concordance with the incidence rates reported per 100 000 total bed days. The overall rate was 42.0 cases per 100 000 population (in the previous quarter the rate was 41.3 per 100 000 population). NHS NWTC is not included due to this being an NHS Special Health Board and therefore not covering a specified population within Scotland.

Incidence rates for this quarter compared with the annual incidence rate for the last twelve months (July 2011 to June 2012) are given in Table 1. Most of the NHS boards have incidence rates for this quarter below or close to their corresponding annual rate. NHS Borders, NHS Dumfries & Galloway, NHS Fife and NHS Tayside have rates which are substantially above the corresponding annual rate.

CDI incidence in patients aged 15-64 years

The total number of cases identified in younger patients during Q3 2012 was 147 (in the previous quarter there were 126 cases). The overall incidence rate for this quarter was 41.6 per 100 000 acute bed days, which is a 21% increase from the previous quarter (34.4 per 100 000 acute bed days).

There was a statistically significant increase in incidence rates in NHS Greater Glasgow & Clyde. Substantial increases in incidence rates occurred in NHS Borders, NHS Dumfries & Galloway, NHS Forth Valley and NHS Grampian (though none were statistically significant). Incidence rates decreased substantially in NHS Fife and NHS Lanarkshire (Figure 5).

Incidence rates in NHS Orkney increased while there were decreases in NHS Western Isles and NHS NWTC. The rates vary widely due to small denominators and overall case numbers were low (Figure 6).

Figures 7 and 8 show that the rates per 100 000 population were in concordance with the incidence rates reported per 100 000 acute bed days. The overall rate was 4.2 cases per 100 000 population (in the previous quarter the rate was 3.6 per 100 000 population).

Incidence rates for this quarter compared with the annual incidence rate for the last twelve months (July 2011 to June 2012) are given in Table 2. Most of the NHS boards have incidence rates for this quarter below or close to their corresponding annual rate. NHS Dumfries & Galloway, NHS Forth Valley, NHS Greater Glasgow & Clyde, NHS Highland and NHS Orkney have rates which are substantially above their corresponding annual rate.

3.2 Identification of outliers

Figures 9 and 10 show funnel plots of CDI incidence rates in patients =>65 years and patients aged 15-64 years, respectively, for all NHS boards during this quarter. There were no NHS boards identified as having an incidence rate above the upper 95% confidence limit during this quarter in either age group.

3.3 Analysis of trends

The trends of CDI incidence rates covering the full surveillance period for both age groups are available for the individual NHS boards from: http://www.documents.hps.scot.nhs.uk/hai/sshaip/publications/cdi/2012/2012-q3-65plus-trend-by-board.pdf and http://www.documents.hps.scot.nhs.uk/hai/sshaip/publications/cdi/2012/2012-q3-15-64-trend-by-board.pdf.

Patients aged =>65 years

Overall, the year on year analysis comparing the period Q4 2010-Q3 2011 with Q4 2011-Q3 2012 indicates a non-statistically significant decrease of 5.4% (95% CI: -17.8% to 8.8%). Figure 11 shows the overall incidence rates from Q4 2006 to Q3 2012.

Year on year analysis shows there was a statistically significant decrease in incidence rates in NHS Dumfries & Galloway. Non-statistically significant decreases were observed in NHS Ayrshire & Arran, NHS Forth Valley, NHS Grampian, NHS Greater Glasgow & Clyde, NHS Lanarkshire and NHS Lothian.

A statistically significant year on year increase was reported in NHS Borders and NHS Fife. In the remaining NHS boards there were non-statistically significant increases over the same period.

Patients aged 15-64 years

Overall, the year on year analysis comparing the period Q4 2010-Q3 2011 with Q4 2011-Q3 2012 indicates a non-statistically significant increase of 0.7% (95% CI: -15.4% to 19.9%). Figure 12 shows the overall incidence rates from Q2 2009 to Q3 2012.

Year on year analysis shows that there were non-statistically significant decreases in NHS Ayrshire & Arran, NHS Greater Glasgow & Clyde, NHS Lanarkshire and NHS Lothian.

A statistically significant increase was reported in NHS Forth Valley and NHS Tayside. In the remaining NHS boards there were non-statistically significant increases over the same period.

Trend analyses in either age group were not carried out for NHS Orkney, NHS Shetland, NHS Western Isles and NHS NWTC due to their reporting no or very few cases over the period.

3.4 Typing and susceptibility data

Ribotype 078 continues to predominate in Scotland accounting for 26.8% (48/179) of all isolates typed from severe cases and/or outbreaks and 26.2% (33/126) of isolates typed from a representative sample of all cases of CDI.

The proportions of types 106 (1.7% and 2.4% from severe cases and/or outbreaks and a representative sample, respectively), 001 (2.8% and 5.6%, respectively) and 027 (3.9% and 1.6%, respectively) remain low compared to previous years. The proportions of the other major ribotypes have not changed compared to the previous quarter.

Of the rarer ribotypes, 026 has increased this quarter (7% prevalence in isolates from severe cases and/or outbreaks) compared to previous quarters (never more than 3%).

A single isolate of a novel ribotype (C. difficile ribotype 244) was identified in Scotland for the first time this quarter. Ribotype 244 has been associated with a significant increase in the incidence rates in Australia since July 2011 where it has become the predominant type. HPS has reported on this finding previously in the HPS Weekly Report at: http://www.hps.scot.nhs.uk/ewr/redirect.aspx?id=53101.

All isolates remain susceptible to vancomycin and metronidazole.

4. Discussion

Incidence rates have increased in both age groups this quarter. Although the increases are not statistically significant, this is the first time since Q3 2011 that incidence rates have increased in the 15-64 years age group, and is the second consecutive increase in rates in the =>65 years age group.

NHS board investigations have not revealed any common links between cases that could explain the increase in incidence rates that have occurred in both age groups this quarter, and statistical analyses have not identified any boards whose incidence rates are an outlier. HPS and SSSCDRL have supported eight NHS boards (including board visits, additional ribotyping of cases, and analysis of CDI data) over the last two quarters where this has been requested by the board.

The increasing incidence rates have coincided with the emergence of C. difficile ribotype 078 in Scotland, which remains the predominant type. However, the lack of outbreaks reported due to this type (none since Q1 2012), and the identification of mixed ribotypes in clusters investigated by boards suggests that the emergence of 078 cannot alone explain the increases observed.

Sub-optimal compliance with standard infection prevention and control precautions (SICPs) and transmission based precautions (TBPs) (especially environmental and equipment cleaning) may be contributing to the general increase observed.

Some boards have noted an increase in CDI occurring in the community but this will require further investigation to determine the burden of community-associated CDI.

Appropriate local monitoring, antimicrobial prescribing and implementation of infection prevention and control at both hospital and community levels are key to maintaining and reducing CDI rates. NHS boards are reminded to follow the national Guidance on Prevention and Control of CDI in Healthcare Settings in Scotland, which includes details on SICPs and TBPs. The Guidance is available from: http://www.hps.scot.nhs.uk/haiic/sshaip/guidelinedetail.aspx?id=42640.

Note:

Caveats for this report may be accessed from: http://www.documents.hps.scot.nhs.uk/hai/sshaip/publications/cdi/2012/methods-caveats-q3.pdf.

Individual CDI rates and denominator data published since October 2006 for each NHS board and overall for Scotland can be accessed from an online appendix: http://www.documents.hps.scot.nhs.uk/hai/sshaip/publications/cdi/2012/2012-q3-appendix-board-bed-days-rates.xls.

Acknowledgement

We would like to thank all the microbiologists and biomedical scientists who have provided and reviewed data for the CDI surveillance programme and the Scottish C. difficile reference service for providing ribotyping data. Information Services Division of the NHS in Scotland is thanked for its statistical support for this report and for providing the hospital activity denominator data. Our thanks also for the continuing hard work of the infection control and antimicrobial management teams in helping to reduce the burden of CDI; they are to be commended for their efforts.

Author(s): Prepared by: The HPS C. difficile Working Group Vol: 47 No: 02 Year: 2013 Page:

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