Staphylococcus aureus bacteremia: what is the impact of oxacillin resistance on mortality?

In order to analyse the impact of oxacillin resistance on the mortality of Staphylococcus aureus bacteremia, and to assess the antimicrobial susceptibility of community-acquired strains in two large university hospitals (the Instituto do Coração do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo and the Instituto Central do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo), we carried out a four-month-long prospective cohort study, which included 163 consecutive cases of S. aureus bacteremia. Of these, 140 (85.9%) were hospital-acquired, 9 (5.5%) were community-acquired and 14 (8.6%) were of indeterminate origin. No cases of community-acquired infection by oxacillin-resistant S. aureus was identified. Among hospital-acquired infections, oxacillin-resistant S. aureus was responsible for 64.3% of cases. Mortality up to 15 days after diagnosis of bacteremia was 27% (18/67) for infections caused by susceptible strains and 33% (32/96) for infections caused by oxacillin-resistant strains (p=0.10). The following independent risk factors for the acquisition of oxacillin-resistant S. aureus were identified in multiple logistical regression analysis: age over 60 years, use of corticoids; presence of a central vascular catheter, and previous use of antibiotics.