S aureus linked to increased mortality risk over time with change in infection source
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For patients receiving maintenance hemodialysis, infection with Staphylococcus aureus bacteremia led to worsening clinical outcomes, including increased in mortality, in a 21-year period.
Further observations from the single-center study suggested the most common suspected sources of infection, identified as central venous catheter or arteriovenous graft at the beginning of the study period, have shifted to non-vascular access sources.
“Compared to the general population, infection-related mortality is up to 100-times greater in patients who receive dialysis. Staphylococcus aureus (S. aureus) is the most common cause of bacteremia in [hemodialysis] HD-dependent patients, accounting for [more than] 30% of all bloodstream infections,” Matthew R. Sinclair, MD, of Duke University Medical Center, and colleagues wrote. “S. aureus bacteremia (SAB) can lead to severe complications, including endocarditis, osteomyelitis, septic arthritis, and abscesses.
Importantly, bacterial genotype plays a critical role in pathogenesis, as methicillin-resistant S. aureus (MRSA) infections are associated with significantly higher mortality than methicillin-susceptible S. aureus (MSSA) infections. MRSA was first isolated in the 1960s and over the past 50 years, nosocomial and community-acquired MRSA infection rates among HD-dependent patients have increased, accounting for [more than] 40% of all S. aureus samples isolated from outpatient HD centers in 2014.”
To examine trends in infection causes and outcomes in the hemodialysis population, Sinclair and colleagues included 453 patients who were hospitalized with S. aureus bacteremia between 1995 and 2015.
Trends in S aureus bacteremia
After adjusting for age and diabetes, researchers found mortality attributable to S. aureus increased by 0.45% per year in the course of the study period, with the suspected source of SAB less likely identified as a central venous catheter (-1.32% per year) or arteriovenous graft (-1.08% per year) and more likely to be identified as stemming from a non-vascular access source (1.89%). In addition, patients with a non-vascular access source were 3.2-times more likely to die as a result of their infection, which the researchers speculated is due to “delays in source control” for causes not related to vascular access.
Sinclair and colleagues noted other trends in the study period, including an increase in persistent bacteremia (0.86% per year) and metastatic infection complications (0.84% per year). Here, they suggested the observed increase in infection with the virulent S. aureus clone USA300 (1.47% per year) “may have contributed to the increase in persistent bacteremia but did not explain the observed increases in SAB-attributable mortality or metastatic complications.”
Mortality in Black vs white patients
Racial differences were also observed, with Black patients with SAB found less likely to die from the infection than white patients. Researchers contended that while this finding is consistent with the “survival paradox” leading to lower mortality for Black patients on hemodialysis compared with white patients, more research is required in this area to adequately understand the interactions between race and clinical outcomes.
“More research is [also] needed to better clarify the clinical impact of the emergence of USA300 among the HD-dependent patients,” Sinclair and colleagues concluded. “We plan to address this in future studies by genotyping bacterial isolates in HD-dependent patients with SAB beyond the year 2015. Determining this will help to decide whether there is future clinical and therapeutic utility in genotyping S. aureus isolates among HD-dependent patients with SAB, or if we should focus exclusively on patient-specific factors to improve outcomes in this patient population.”
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