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MRSA surveillance system: Results

Author:

Health Protection Agency. Communicable Disease Surveillance Centre,Department of Health
Published date:

7 March 2005
Primary audience:

Professionals
Publication format:

Electronic only
Gateway reference:

2005
Pages:

10
Copyright holder:

Crown

These tables give data on numbers and rates of MRSA bacteraemias per 1000 bed days in NHS acute Trusts: Mandatory surveillance - April 2001-September 2005. The data was produced by the Health Protection Agency Communicable Disease Surveillance Centre for the Department of Health.

MRSA surveillance system - Results

Results of the Department of Health's mandatory methicillin resistant Staphylococcus aureus (MRSA) surveillance system in acute Trusts in England. These figures are published every six months. Data is also presented as a summary of annual numbers for the four complete years of the surveillance system.

MRSA bacteraemia (bloodstream infections) numbers and rates by individual named Trusts are now available for the period April to September 2005. Results for the first four years of the mandatory surveillance system (April 2001-March 2005) are also included in the tables.

In order to allow some comparison of similar institutions acute NHS Trusts have been categorised into:

'single specialty' Trusts (for example, Trusts only undertaking orthopaedics or cancer or children's health services);
'specialist' Trusts (Trusts with specialist services which receive patients referred from other Trusts for these services);
'general acute' Trusts (Trusts providing general acute healthcare services).

These data show that MRSA rates tend to be highest in specialist Trusts and lowest in single specialty Trusts. This is not surprising as MRSA bacteraemia rates will be higher in Trusts that have more vulnerable patients and that undertake more invasive and high-risk specialist care. This does not mean that these Trusts are poor performers in either infection control or other performance measures. In other Trusts the MRSA bacteraemia rate may be low because they have less vulnerable patient groups. In addition the MRSA may not have been acquired in the reporting Trust. A proportion of bacteraemias in all types of hospital are preventable and the aim is to lower bacteraemia rates overall. Thus, the important thing is that all Trusts are examining their MRSA bacteraemias to assess how much is preventable and to take appropriate control measures.

National data

The total number of methicillin-resistant Staphylococcus aureus bacteraemias in England in April to September 2005 was 3580. The corresponding figure for the same time period in the previous four years was 3616 (2001), 3584 (2002), 3749(2003) and 3525 (2004).
The number of MRSA bacteraemias in the first four complete years of the mandatory recording system were 7247 in 2001/02, 7372 in 2002/03, 7684 in 2003/04 and 7212 in 2004/05.

Interpretation of the data

These data are not straightforward and need to be interpreted with care, taking the following into account:

The individual Trust figures reflect the burden of serious infections associated with MRSA bacteraemia (or blood stream infections) and not all MRSA infection or carriage. An MRSA bacteraemia report is made when MRSA is detected in a blood sample.
The MRSA bacteraemias reported by an acute Trust were not necessarily acquired in that Trust. There is much patient transfer between hospitals, such that a patient requiring specialist care may be transferred to a Trust with a specialist unit for their particular condition. When their care is complete, they may then return to the originating hospital. In this way Trusts may import MRSA from other hospitals or from the community.
Not all acute Trusts are the same. Some have specialist units which receive referrals from other acute Trusts (e.g., renal or cancer units), while others include units which in other places form part of other types of Trusts, such as community or mental health Trusts. (Non-acute NHS Trusts are not included in the mandatory reporting scheme.) This means that it is not valid to compare one hospital Trust with another. The effect can be partly overcome by categorising Trusts as specialist, general acute, or single specialty, but this will not overcome all these difficulties. This requires more detailed local analyses incorporating information on risk factors and case mix.
These differences in the make-up of different Trusts also have an effect on their MRSA rate. A Trust that has a high preponderance of units with more patients vulnerable to MRSA, such as specialist surgical units, is quite likely to experience a higher rate than a Trust that has a high proportion of lower risk units (e.g., maternity or paediatric wards) where patients are unlikely to experience MRSA bacteraemia. Thus, although a Trust may have a high rate, this does not necessarily reflect an infection control problem in the Trust. Rather, the rates, particularly if high, should form the basis of further investigation.
The bed occupancy figures used to derive the MRSA bacteraemia rates in the period April to September 2005 are from a period before the MRSA data. This may affect a Trust's rate if there has been a significant change in activity that is not yet reflected in the bed occupancy figure. These rates will be updated when the bed occupancy figures for this period are available. The rates for the first four years (April 2001-March 2005) have been calculated using the bed occupancy figure for each year.
All the bed occupancy figures used to calculate the rates apply only to overnight admissions. Consequently MRSA bacteraemias in patients who are not admitted overnight, e.g., in renal units, may make a Trust's rate look falsely high, as these patients will feature in the numerator but not in the denominator.
Finally, in a six month period, only a few bacteraemias may be reported. This means that in smaller Trusts, changes of one or two reports can cause large fluctuations in MRSA rate, which can be misleading when making comparisons of values or rates.

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