Long-term methicillin-resistant Staphylococcus aureus bacteremia persisting for more than 2 weeks: risk factors and outcomes.

The clinical significance of long-term methicillin-resistant Staphylococcus aureus (MRSA) bacteremia remains unclear. We evaluated the clinical, microbiological characteristics, and clinical outcomes of long-term MRSA bacteremia. A nested case-control study was conducted in a prospective cohort of adult patients with MRSA bacteremia at a tertiary hospital between August 2008 and December 2017. Patients with long-term MRSA bacteremia (≥ 14 days) were compared with control patients, defined as having bacteremia that resolved in less than 3 days. The following variables were documented: heteroresistance phenotype, genotypes, agr dysfunction, and the presence of 41 virulence genes in isolates. Of the total 890 patients studied, 69 patients (7.8%) exhibited long-term MRSA bacteremia and 599 (67.3%) exhibited resolving bacteremia. The most common sources of long-term bacteremia were central venous catheter-related infection (39%) and osteomyelitis (19%). Independent risk factors for long-term MRSA bacteremia included male sex (adjusted odds ratio [aOR] = 2.43), community-acquired bacteremia (aOR = 2.93), the presence of a prosthetic device (aOR = 3.40), and osteomyelitis (aOR = 7.98). Metastatic infections developed more frequently in patients with long-term bacteremia than in those with resolving bacteremia (56.5% vs. 8.0%; P < 0.001). Although there were no significant differences in 30-day, 12-week, or in-hospital mortality rates between the two groups, infection-attributable mortality was higher in the long-term bacteremia group (23.2% vs. 11.5%; P = 0.01). Microbiological characteristics did not differ significantly between the two groups. Clinical factors, including community-acquired bacteremia, the presence of a prosthetic device, and osteomyelitis, appear to contribute to long-term MRSA bacteremia more than microbiological factors.