Evaluation of the Cefazolin Inoculum Effect (CzIE), measuring the burden of infection, and the impact on outcomes in patients with Staphylococcus aureus bacteraemia

• In patients with significant S. aureus infection, cefazolin is increasingly used in preference to isoxazolyl penicillins such as flucloxacillin.
• However, if using cefazolin, it has been suggested that clinical outcomes might be negatively impacted in a subset of patients with an S. aureus strain demonstrating the cefazolin inoculum effect (CzIE).
• The study aims to utilize a robust laboratory phenotypic method for CzIE detection, identification of surrogate measures of high inoculum S. aureus infection, and assessing the clinical impact of having a CzIE strain in a high inoculum infection.
• Following this initial CzIE analysis, a further exploratory analysis will incorporate genotypic associations with the CzIE and whether there are associations between genotypes (eg. type A and C blaZ alleles) and clinical outcomes.

‍