Cases were identified by data extraction from the Pathology North and Pathology Queensland laboratory information systems (AUSLAB; PJA, Melbourne). Clinical and demographic data on all significant bloodstream infections were prospectively collected as routine surveillance by the infection control and microbiology services. Relapsed cases were retrospectively identified from laboratory data. Outcomes were determined at 28 days post initial positive blood culture for all cases and controls.
In addition to demographic details, clinical variables recorded included source of infection, hospital location, co-morbid conditions, admitting clinical service, acquisition status of infection, initial antibiogram of the blood culture isolate (AmpC de-repressed phenotype), the presence of vascular access devices and the neutrophil count on the day of first positive blood culture. Data on antibiotic use and SAPS II physiology scores [26 (link)] (determined on the day of first positive blood culture) were recorded from clinical chart review. Only antimicrobial agents with Gram-negative activity were recorded, with those used within the first 48 h after initial blood culture defined as empirical use and those prescribed after blood culture results available defined as definitive use. Healthcare acquisition and source designation of the bacteraemia were categorised according to standard definitions [27 –29 ]. Empirical antibiotic therapy was described as appropriate if the isolate was susceptible to at least one agent used. If an agent was used for ≥50% of the definitive treatment duration, this was listed as the primary agent. If a second agent was used either concurrently or sequentially, the patient was described as receiving combination therapy; if combination therapy was used for the majority of the definitive treatment duration the antibiotic choice was determined as ‘other’. For statistical analysis, if the definitive regimen included a carbapenem, quinolone, co-trimoxazole, cefepime or an aminoglycoside to which the isolate was susceptible, the treatment was classified as ‘standard therapy’, if piperacillin-tazobactam or ticarcillin-clavulanate was used and the isolate was susceptible, the treatment was classified as ‘BLBLI’, otherwise the treatment was defined as ‘inappropriate’ (e.g. cephalexin, cephazolin, ceftriaxone, ampicillin/amoxicillin, amoxicillin-clavulanate or no therapy). Standard dosing regimens at participating hospitals for piperacillin-tazobactam are 4.5 g 8-hourly and ticarcillin-clavulanate 3.1 g 6-hourly, with dose adjustment for renal dysfunction according to the Australian Therapeutic Guidelines [30 ]. Patients were classified as being immunosuppressed if they had the following conditions: neutropenia (neutrophil count <0.5 x109/L), haematological / solid organ malignancy or myelodysplastic syndrome, solid organ transplant or if they received any other immunosuppressive drug therapy including prolonged high dose corticosteroids (≥30 mg prednisolone or equivalent daily).
In addition to demographic details, clinical variables recorded included source of infection, hospital location, co-morbid conditions, admitting clinical service, acquisition status of infection, initial antibiogram of the blood culture isolate (AmpC de-repressed phenotype), the presence of vascular access devices and the neutrophil count on the day of first positive blood culture. Data on antibiotic use and SAPS II physiology scores [26 (link)] (determined on the day of first positive blood culture) were recorded from clinical chart review. Only antimicrobial agents with Gram-negative activity were recorded, with those used within the first 48 h after initial blood culture defined as empirical use and those prescribed after blood culture results available defined as definitive use. Healthcare acquisition and source designation of the bacteraemia were categorised according to standard definitions [27 –29 ]. Empirical antibiotic therapy was described as appropriate if the isolate was susceptible to at least one agent used. If an agent was used for ≥50% of the definitive treatment duration, this was listed as the primary agent. If a second agent was used either concurrently or sequentially, the patient was described as receiving combination therapy; if combination therapy was used for the majority of the definitive treatment duration the antibiotic choice was determined as ‘other’. For statistical analysis, if the definitive regimen included a carbapenem, quinolone, co-trimoxazole, cefepime or an aminoglycoside to which the isolate was susceptible, the treatment was classified as ‘standard therapy’, if piperacillin-tazobactam or ticarcillin-clavulanate was used and the isolate was susceptible, the treatment was classified as ‘BLBLI’, otherwise the treatment was defined as ‘inappropriate’ (e.g. cephalexin, cephazolin, ceftriaxone, ampicillin/amoxicillin, amoxicillin-clavulanate or no therapy). Standard dosing regimens at participating hospitals for piperacillin-tazobactam are 4.5 g 8-hourly and ticarcillin-clavulanate 3.1 g 6-hourly, with dose adjustment for renal dysfunction according to the Australian Therapeutic Guidelines [30 ]. Patients were classified as being immunosuppressed if they had the following conditions: neutropenia (neutrophil count <0.5 x109/L), haematological / solid organ malignancy or myelodysplastic syndrome, solid organ transplant or if they received any other immunosuppressive drug therapy including prolonged high dose corticosteroids (≥30 mg prednisolone or equivalent daily).
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