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Hospital Performance: Healthcare-associated Staphylococcus aureus bloodstream infections in 2011–12

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Introduction

Healthcare-associated infections are acquired by patients while receiving medical care either in hospital or from other heath care services. This report deals with infections diagnosed as S. aureus bloodstream infections, and deemed by specialist infection control officers to have been acquired while receiving care from a hospital (Box 1).

Measures presented

The following measures are presented in the report. Only the 352 hospitals with more than 5,000 patient days monitored by infection control systems are included in these calculations:

  • Rate of healthcare-associated S. aureus bloodstream infection, by hospital (see Box 1)
  • Total number of hospitals in peer group: sums the hospitals within each peer group
  • All cases reported nationally (%): presents the percentage of healthcare-associated S. aureus bloodstream infections attributable to each peer group
  • All patient bed days monitored (%): presents the percentage of patient bed days monitored and reported to the National Staphylococcus aureus Data Collection 2011–2012, for this peer group
  • Average cases per 10,000 patient days: presents the rate of healthcare-associated S. aureus bloodstream infections (see Box 1) attributable for all patient episodes in each peer group
  • Range of patient bed days monitored (%): presents the range in the coverage of infection monitoring systems in hospitals across this peer group. This presents the minimum and maximum coverage rates.

The following measures are presented, by hospital, on the www.myhospitals.gov.au website:

  • Number of cases of S. aureus bloodstream infection
  • Number of patient bed days monitored by infection control surveillance
  • Rate of healthcare-associatedS. aureus bloodstream infection (see Box 1).

The website presents all data submitted for healthcare-associated S. aureus bloodstream infections and is not limited to >5,000 patient bed days except when presenting rate. The following four hospitals have their cases and patient bed days under surveillance added to a larger hospital operating under the same governance arrangements:

  • Kalamunda Hospital into Swan District Hospital (WA)
  • Royal Perth Hospital Shenton Park Campus into Royal Perth Hospital Wellington Street Campus (WA)
  • Kaleeya Hospital into Fremantle Hospital (WA)
  • St. Margaret’s Hospital into the Queen Elizabeth Hospital Campus (SA).

Box 1: Rate of healthcare-associated Staphylococcus aureus bloodstream infection

Description: The number of cases of S. aureus bloodstream infections per 10,000 patient bed days under infection surveillance.

Data source: The National Staphylococcus aureus Bacteraemia Data Collection 2011–2012 as supplied by the Australian Institute of Health and Welfare.

Numerator: Number of cases of healthcare-associated S. aureus bloodstream infections reported (defined below).

Denominator: Number of patient bed days monitored by S. aureus bacteraemia surveillance arrangements.

Computation: 10,000 × (Numerator ÷ Denominator).

Defining a case of S. aureus bloodstream infection

A patient episode (case) of S. aureus bacteraemia is defined as a positive blood test for Staphylococcus aureus. For surveillance purposes, only the first isolate per patient is counted, unless at least 14 days has passed without a positive blood culture, after which an additional episode is recorded.

A case of S. aureus bloodstream infection is considered to be healthcare associated if the first positive blood test is more than 48 hours after hospital admission or less than 48 hours after discharge, or, if the first positive blood test is 48 hours or less after admission and one or more of the following criteria was met:

  1. S. aureus bacteraemia is a complication of the presence of an indwelling medical device (for example, intravascular line, haemodialysis vascular access, cerebrospinal fluid shunt, urinary catheter)
  2. S. aureus bacteraemia occurs within 30 days of a surgical procedure where the infection is related to the surgical site
  3. An invasive instrumentation or incision related to the S. aureus bacteraemia was performed within 48 hours
  4. S. aureus bacteraemia is associated with neutropenia (<1 x 109) contributed to by cytotoxic therapy.

Additional notes

Although the following inclusion and exclusion criteria are specified by the Australian Institute of Health and Welfare for the National S. aureus Bacteraemia Data Collection, states and territories vary in their interpretations of national definitions used when providing data.

For example, one state has always included unqualified newborn days in the denominator while another does not.

Inclusions: Unqualified newborn days are included in the patient day denominator. All newborns are monitored by surveillance programs, thus their patient bed days are included in the denominator.

Exclusions: Hospital boarders and posthumous organ procurement episodes are explicitly excluded from the calculation and are not covered by infection surveillance programs.

Only episodes associated with public hospital care in each jurisdiction should be counted. If a case is associated with care provided in another jurisdiction (cross-border flows) then it is reported, where known, by the jurisdiction where the care associated with the S. aureus bloodstream infection occurred.