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S. aureus bacteremia: Not a ‘static’ syndrome
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The clinical characteristics and epidemiology of Staphylococcus aureus bacteremia, or SAB, have changed over the past 2 decades, according to researchers, who suggested that systemic monitoring of complications and identifying the emergence of hypervirulent clones through the genotyping may improve its clinical management.
“This study indicates that the syndrome we clinicians recognize as SAB is not static. The patients have changed, with more comorbid conditions and more indwelling prosthetic material,” Vance G. Fowler, MD, professor of medicine at Duke University School of Medicine, told Infectious Disease News. “The bacteria causing SAB have also changed, with new bacterial clones arising and inexplicably replacing other strains. The rise in sicker patients and more virulent strains of S. aureus have led to shifts in the type and frequency of infectious complications encountered among patients with SAB in the 21st Century.”
At Duke University between January 1995 and December 2015, Fowler and colleagues enrolled patients with monomicrobial SAB in a longitudinal study to evaluate changes in the clinical presentation and epidemiology of the syndrome.
Of the 2,348 eligible patients, 54.2% had some type of an implantable device, such as a central vascular catheter, cardiac device, vascular graft or orthopedic implant. Over the 21-year study period, the proportion of patients with an implantable foreign body significantly increased at an annual rate of 0.96% (P = .002). The researchers also observed a significant increase in comorbid conditions and the proportion of patients who acquired SAB outside the hospital. However, they noted that the study findings confirm that SAB is primarily a consequence of health care contact. Additionally, metastatic complications significantly increased at an annual rate of 0.94% (P = .019).
Genotyping of corresponding bloodstream S. aureus isolates using spa typing revealed a significant decline in the prevalence of spa-CC012 (multi-locus sequence type [MLST] CC30), spa-CC004 (MLST CC45), spa-CC189 (MLST CC1) and spa-CC084 (MLST CC15) during the study period. Genotyping also revealed a significant increase in spa-CC008.
In general, patients with SAB caused by spa-CC008 were significantly more likely to develop metastatic complications. Fowler and colleagues noted that, in particular, these patients were significantly more likely to develop abscesses, septic emboli and persistent bacteremia.
“These findings demonstrate shifts in bacterial genetics can have significant consequences in the infections that they cause,” Fowler said. “Interestingly, most of these shifts in bacterial genotypes and severities of infections are likely to go unnoticed by the busy practitioner.”
The researchers emphasized the potential benefits of bacterial genotyping and keeping track of the rates of complications from SAB.
“It would be important to test the extent to which systematic approaches for bacterial genotyping and recording rates of specific complications could improve clinical management by detecting subtle shifts in clinical syndromes that herald the emergence of a new, hypervirulent bacterial clone,” Fowler said. - by Marley Ghizzone
Disclosures: Fowler reports numerous ties to industry. Please see the study for all authors’ relevant financial disclosures.
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