Molecular characteristics of Staphylococcus aureus associated prosthetic joint infections after hip fractures treated with hemiarthroplasty: a retrospective genome-wide association study

Objectives: To characterize clonality, virulence, and resistance patterns associated with hip hemiarthroplasty (HHA) Staphylococcus aureus prosthetic joint infections (PJIs), potentially explaining the high incidence of 1-year mortality among HHA patients. Methods: A retrospective bacterial genome-wide study of orthopaedic patients treated between 2000-2017 at Akershus University Hospital, Lørenskog, Norway was performed. Patients with S. aureus PJIs following hip fracture-related hemiarthroplasty were compared to patients with non-HHA lower-extremity implant-related S. aureus infections. Clinical data were collected from patients’ electronic medical records. S. aureus isolates from diagnostic patient samples were whole-genome sequenced using Illumina’s MiSeq platform. Multi locus sequence type and clonal complex (CC) were extrapolated from WGS data. Univariate and multivariate bioinformatics analyses were performed to detect genetic signatures associated with either group. Results: In total, 62 HHA patients and 73 non-HHA patients were included. Mean age (81 years vs. 74 years; p7%. Intergroup CC distributions were similar (p=0.131). Core and accessory genome analyses, including virulence and resistance genes and k-mer analysis revealed few group-correlated variants. Conclusions: Despite having performed a comprehensive genome wide association study, few molecular differences in S. aureus causing infection in patients with HHA or non-HHA were identified and none could explain the elevated 1-year mortality in HHA patients. Our findings support the premise that all S. aureus can cause invasive infections given the opportunity.