Staphylococcus aureus bacteraemia as a quality indicator for hospital infection control

Methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia is a frequent and dangerous complication of modern health care. At the very minimum, an episode of MRSA bacteraemia increases length of stay in hospital and has substantial financial costs, but some series have suggested that MRSA bacteraemia is associated with a mortality rate of 20%–25%.1 In Western Australia, all MRSA infections have been notifiable since 1985.2 In the United Kingdom, mandatory reporting of MRSA bacteraemia by National Health Service Trust hospitals commenced in May 2001.3

What is not always appreciated is that methicillin-susceptible S. aureus (MSSA) bacteraemia is also a serious health care-associated infection. In 2005, a report estimated a median rate of hospital-onset S. aureus bacteraemia (SAB) across 17 Australian hospitals of 0.7 cases per 1000 admissions.4 In 2006, there was a call for SAB, whether due to methicillin-resistant or methicillin-susceptible strains, to be used as a quality indicator for hospital infection control programs.5 Accordingly, a report from the Australian Commission on Safety and Quality in Health Care in 2008 identified health care-associated SAB as a key outcome measure for the National Hand Hygiene Initiative.6 While WA has been the leader with respect to MRSA notification, Tasmania recently went further and has made all cases of SAB notifiable, regardless of whether they are health care-related.7

Since 2001, Austin Health has had a strong focus on control of MRSA through the introduction of an institution-wide program to provide and promote alcohol-chlorhexidine hand hygiene for all health care workers, and alcohol wipes for all shared equipment.8 The rate of MRSA infections has fallen progressively over 7 years at Austin Health, and episodes of MRSA bacteraemia have become statistically less useful as a performance indicator. However, we, like others, observed patients with MSSA bacteraemia that was likely to be hospital-acquired.4,5 To address this problem, we introduced the “AuSABs” (Austin-associated S. aureus bacteraemias) program, whereby all episodes of SAB, not just those caused by MRSA, were made quality indicators. In this report, we evaluate the effectiveness and practicality of our AuSABs program.

The AuSABs program was designed and introduced at Austin Health, a large University of Melbourne teaching health service with three separate hospital campuses, but a single, central microbiology laboratory service. The program was progressively developed and rolled out over 9 months from January 2006, and we continued to review the impact over the subsequent 18 months.

Every SAB detected in our microbiology laboratory that was linked to an Austin Health patient triggered a review of the case (when possible, on the same day or next normal working day) by an infection control clinical nurse consultant and/or infectious diseases registrar. This review was separate from the immediate clinical management of the patient, which remained the responsibility of the unit under which the patient was admitted. We recorded the likely place of acquisition (community or hospital), admitting unit, likely source, presence of any vascular access device and, if applicable, details of device insertion and management. Any potential system errors that may have contributed to the episode were noted.

An episode of SAB, including its association with a vascular device, was defined according to published criteria (Box 1).9,10 As part of our program, we introduced the term “AuSAB” (meaning SAB associated with health care at Austin Health), instead of “health care-associated SAB”, to encourage a sense of ownership and responsibility for these adverse events at Austin Health. Where possible, the source of bacteraemia was determined by identification of a primary focus, which was confirmed where possible by isolating S. aureus with the same antibiogram from that site.

Patients were followed until hospital discharge or 30 days after the episode of SAB. In the event of a patient’s death, the AuSAB was retrospectively categorised as “contributory” or “non-contributory” to the death by consensus among a panel of infectious diseases physicians and registrars who were presented with de-identified patient information that included the admission diagnosis, underlying comorbidities, clinical history, and timing of the AuSAB episode in relation to the time of death.

Blood cultures were ordered as clinically indicated, and MRSA and MSSA isolates were identified by standard techniques.11 Isolates from episodes of AuSAB were examined for clonality by means of pulsed-field gel electrophoresis (PFGE) of SmaI digests of chromosomal DNA. The resulting PFGE pattern was analysed using GelCompar II, version 3.5 (Applied Maths NV, Sint-Martens-Latem, Belgium), as described previously.12 PFGE digestion patterns were considered clonal if GelCompar estimated a similarity of ≥ 80%.12

During the initial 9 months of the program, infection control staff publicised and explained the new program to hospital staff in the clinical areas in which AuSABs were being identified. The program included prompt investigation of every AuSAB by infection control staff, followed by “real time” feedback to relevant wards and departments. The feedback included the patient’s name, the original reason for admission, and ways in which this episode could have been prevented, as we believed that linking an adverse event to an individual patient was likely to motivate change more strongly than just providing statistical rates. Based on investigation and discussion with relevant clinicians, infection control staff recommended changes in practice and education sessions in these high-risk clinical areas. Reassessments were performed to monitor adherence to recommended interventions, and to provide further assistance as required.

The AuSABs quality improvement program was associated with a 55% reduction in hospital-acquired SABs, probably preventing 80 costly and potentially fatal infections. From the outset, we deliberately named the program “AuSABs” for Austin-associated S. aureus bacteraemias to remind us and other Austin Health departments that these adverse events occur on our watch, are frequently preventable and are our responsibility. By refocusing our existing MRSA bacteraemia surveillance system to include all SABs, we uncovered a large, under-recognised burden of health care-associated bloodstream infection at our institution. A caveat to our report on this program is that it is a quality improvement project, and not research. The interventions were introduced progressively, and there was no application of randomised controlled methods. Therefore, we cannot assess the relative effectiveness of any one intervention, nor be certain that the improvement we observed was causally linked to our interventions. However, the program has several merits.

Episodes of SAB are an unambiguous marker of invasive infection, and more than half of the episodes we observed were health care-related. By monitoring all health care-associated SABs and not just MRSA, as with our previous strategy,8 we detected 90 additional health care-associated SABs (of a total 131 [68.7%]) that were caused by MSSA. We also detected 35 health care-associated SABs in non-inpatients (26.7%), which may have been missed by a ward-based surveillance program, and even more may have been missed if we had aimed the surveillance program at high-risk wards, such as the intensive care unit, only. Our program showed that vascular access device-related bacteraemias accounted for 49.6% of AuSABs, and many of these were associated with system errors that were previously undetected, and were potentially preventable. Others have also suggested there is great potential within hospitals to reduce or nearly eliminate nosocomial infections, in particular catheter-related bacteraemias.13-23 Furthermore, the multifaceted interventions used in our program, including staff education, nurse empowerment, intervention bundles and checklists, are relatively simple to implement in busy hospitals, and have proved to be sustainable.23

The PFGE typing of our AuSAB isolates showed an expected pattern for MRSA, with a restricted number of previously recognised hospital-endemic clones. However, for the MSSA isolates, the PFGE showed a much greater diversity of clones, implicating varied sources and modes of transmission. These data suggest that many of these infections arise from strains already colonising patients at the time of admission, and are not the result of cross-transmission. However, we cannot exclude some degree of cross-transmission of MSSA. Hence, to prevent MSSA AuSAB infections, we needed to not only focus on staff hand hygiene, as we had for controlling endemic MRSA, but to review protocols and practices for inserting devices that breach skin, or accessing existing lines.

This quality improvement program was simple to perform and required relatively little time to maintain, at an estimated annual cost of $7000–$9000 (a proportion of 0.1 of an infection control clinical nurse consultant salary). Our findings mirror results obtained with a similar program at Canberra Hospital.14 Compared with the small cost of establishing the program, the economic costs of health care-associated SABs are huge. Estimates vary, but in the United States, the cost of an episode of SAB ranges from US$20 000 to US$50 000.1,15,16 Financial data for Australia are scarce, but assuming a cost of A$22 000 per episode,5 the total AuSAB cost at our institution for 27 months was almost $3 million. So, the annual cost of running the program ($7000–$9000) was less than half the cost of one episode of SAB. By preventing an estimated 80 AuSAB infections, the program may have saved our institution $1.75 million, and prevented 5–6 deaths over 27 months.

The AuSAB program is now core business for our infection control team, with investigation and feedback integrated into the team’s daily activities. Results are reported to the hospital executive, and are used as a performance indicator by the Infection Control Committee. The data generated from our program are also useful for comparison with other Australian hospitals, and the AuSAB rate has fallen below the previously published national median of 0.7 per 1000 admissions.4 At Austin Health, our overall performance target is now less than 0.5 AuSABs per 1000 separations, but our target for those that are line-related should be close to zero.23 The introduction of institution-wide SAB surveillance and feedback is a first step towards this goal.

2 Rates of Staphylococcus aureus bacteraemia associated with health care at Austin Health (AuSAB), with fitted computer-generated linear regression curve