Linezolid-resistant staphylococcal bacteremia: a multicenter case-case-control study in Italy

The aim of our multicenter study is the analysis of the characteristics of patients with bloodstream infections due to staphylococcal strains resistant to linezolid. This was a retrospective case-case-control study of patients hospitalized in three large teaching hospitals in Italy. The linezolid-resistant Staphylococcus spp. (LIN-R) group and the linezolid-susceptible Staphylococcus spp. (LIN-S) group were compared to the controls to determine the clinical features and the factors associated with the isolation of LIN-R strain. All LIN-R Staphylococcus spp. strains were molecular-typed. Compared to LIN-S group, the central venous catheter (CVC) was the main source of infection in the LIN-R group. The LIN-R and LIN-S groups showed a similar incidence of severe sepsis or septic shock and both showed a higher incidence compared to the control group. Overall, the patients in the LIN-R group had a higher 30-day mortality. Multivariate analysis found previous linezolid therapy, linezolid therapy >14 days, antibiotic therapy in the previous 30 days, antibiotic therapy >14 days, previous use of ≥2 antibiotics, and hospitalization in the previous 90 days as independent risk factors associated with isolation of linezolid-resistant strain. G2576T mutation in domain V of 23S rRNA was the principal mechanism of resistance; only one S. epidermidis strain carried cfr methylase gene (A2503), together with L4 insertion (71GGR72), and L3 substitution (H146Q). LIN-R strains are associated with severe impairment of clinical conditions and to unfavorable outcome of patients. The reinforcement in infection control measures might have a crucial role in this type of infection.